Offering a full and comprehensive service, our long-standing and experienced farm animal department focuses on animal productivity and welfare. We aim to collaborate with farmers, seeing a team approach as the best way to plan and protect herd health in both the short and long term. Just some of the services we provide are as follows:
- Attending to and treating sick animals
- Disease diagnosis
- Haematology, biochemistry and mineral profile blood testing
- Attending calving complications
- Routine farm work such as TB testing
- Routine procedures such as castration and dehorning
- Fertility work including repeat breeders, non-cycling cows and pregnancy diagnosis and ultrasound scanning
- Abortion diagnosis
- Advice sessions including vaccination programmes, herd health and disease prevention programmes
IBR is caused by the bovine herpes virus. This virus causes three different types of disease: respiratory disease (IBR), venereal disease, and brain disease in calves. The last two are much less common than respiratory disease
- Nasal discharge (can be clear but is often milky-white)
- Conjunctivitis (red eyes)
- High temperature
- Loss of appetite
- Dramatic drops in milk yield may be first sign
- Difficulty in breathing and coughing may occur but not consistently
- Death can occur in severe cases
- Abortion is seen in some animals with clinical signs.
- On the clinical signs described above. The signs of IBR are very variable. In some outbreaks, little more than a runny nose and red eyes is seen (although drops in milk yield can be large despite the apparently mild disease).
- Unlike PI3 and RSV (the other two main viruses), IBR is commonly seen in adult cattle.
- Your vet can take samples for virus testing from the respiratory tract or conjunctiva
- Blood testing for antibodies can identify infected cattle, particularly if paired samples are taken
- Post mortem examinations are very useful in severe outbreaks, as other disease such asPasteurella may be involved
- Diagnosis on a herd basis can be made using a combination of blood tests and milk tests. Ask your vet for advice
- Antibiotics are useful on preventing and treating infection by bacteria, which often develops after IBR starts.
- Vaccination in the face of an outbreak can be beneficial in reducing its spread
- Biosecurity – Cattle are the main source of the virus, virtually all farms with an IBR problem have bought it in. The main source of the virus is not animals with disease but animals that have recovered from disease, as these cattle still have the virus in their body (they are ‘latently’ infected) You should not buy antibody positive cattle if you are IBR free
- Vaccination – There are several effective vaccines on the market, discuss with your vet which is the best for you.
Leptospirosis is a common infection in dairy and beef herds.
Economic losses result from
- Poor milk yield
Leptospirosis is a common cause of abortion in dairy and beef herds
Leptospirosis can cause milk drop affecting a large proportion of the herd.
Leptospirosis affects humans causing influenza-like symptoms with severe headaches but can be treated effectively. Dairy farmers are particularly at risk of infection from urine splashing onto the face whilst milking the cows. Pasteurisation destroys all leptospire organisms excreted in milk.
The two important types of Leptospira hardjo are Leptospira borgpetersenii serovar Hardjo and Leptospira interrogans serovar Hardjo. Infection arises from contact with infected urine or the products of abortion. Disease is spread most often during the spring and summer months while cattle are at pasture. Leptospires are susceptible to drying, exposure to sunlight, pH<5.8 or extremes of temperature. Leptospira Hardjo is not carried by vermin or wildlife but sheep can carry and excrete Leptospira Hardjo therefore mixed grazing is a risk factor.
Disease is spread most often during the spring and summer months while cattle are at pasture.
The important risk factors for leptospirosis are:
- Open herds
- Using shared bulls
- Mixed grazing with sheep
- Shared grazing with common watercourses
A sudden drop in milk yield occurs two to seven days after infection of susceptible cows. The udder becomes soft and flabby with colostrum-like secretions or blood-tinged milk in all quarters. Signs may be mild and go undetected but some cows become lethargic and stiff with a fever and reduced appetite. Abortion may occur three to 12 weeks following infection with most abortions occurring during the last three months of pregnancy. Infection may also produce premature and weakly calves.
There is circumstantial evidence of infertility following isolation of Leptospira Hardjo from the reproductive tract of a high percentage of repeat breeder cows. Leptospira Hardjo may also cause embryonic death. Venereal transmission is possible but may not adversely affect the pregnancy rate because Leptospira Hardjo is killed by uterine defences during oestrus. Split-herd vaccination trials have shown improved fertility parameters in vaccinated cows in herds with endemic Leptospira Hardjo infection.
There are numerous causes of a marked drop in the volume of milk recorded from the bulk tank which your veterinary practitioner will consider (large numbers of cows affected) including:
- sudden changes in feeding regimen,
- bovine virus diarrhoea infection (BVDV)
- lungworm infestation,
- infectious bovine rhinotracheitis (IBR),
- bovine respiratory syncytial virus (BRSV),
- influenza A.
The common causes of abortion include:
- Neospora caninum
- BVDV infection
- Salmonella spp.
- Bacillus licheniformis
Various tests detect antibodies to Leptospira Hardjo in blood samples with serum MAT titres of >1/100 considered to be significant.
Dam serology is of limited use because the MAT titre may fall rapidly after acute infection and be negative at the time of abortion; a positive result may only reflect previous exposure. During an abortion outbreak MAT titres >1/400 in some aborted cows are likely to be meaningful. ELISA titres are reported to remain positive for much longer following infection so may simply indicate previous exposure.
Antibodies in foetal fluids may indicate exposure to Leptospira Hardjo in utero after four months’ gestation however the foetus may die before mounting an immune response.
Fluorescent antibody test (FAT) to detect Leptospira Hardjo antigen in foetal tissues, e.g. kidney and lung is the best available test to confirm a diagnosis of abortion but delays in sample submission lead to rapid sample autolysis adversely affecting the test.
Herd screening tests
A bulk milk ELISA test is available and can be monitored regularly as part of surveillance programme in a naïve herd. Pooling milk samples from first lactation heifers is a useful way of monitoring the infection status in a herd.
Control of Leptospira Hardjo in cattle herds relies upon a combination of management decisions to reduce risk of infection, strategic antibiotic treatment, and vaccination. The primary course of immunisation consists of two injections four weeks apart followed by annual boosting. Vaccination should prevent urine shedding following exposure and will protect against milk drop and abortion.
Strict biosecurity measures and a robust herd health plan are essential to prevent introduction of BVDv into your herd; effective biocontainment measures are essential on those farms with active infection to reduce the costs of BVD and to, eventually, eradicate BVDv from the herd
The main transmission route is by direct contact with cattle persistently infected with BVD virus. It needs only one persistently infected animal to be introduced into a susceptible herd to cause very significant financial losses.
Cattle exposed to BVD virus may show few clinical signs, producing protective antibodies within three to four weeks. In some situations, BVD virus infection may temporarily lower immunity to other infectious diseases exacerbating these clinical infections particularly in young calves.
BVD virus infection may temporarily lower immunity to other infectious diseases such as
- Respiratory infections,
BVD virus during early pregnancy causes embryonic death and return to oestrus, foetal death/abortion, mummification of the foetus, birth defects of the nervous system and eyes, weak/premature calves, and live persistently-infected calves.
BVD virus is most important when it infects susceptible breeding cattle during early pregnancy causing foetal death/abortion, and weak/premature calves.
Infection of the foetus before 110/120 days of pregnancy results in the birth of a live calf but persistently infected (animal carries the virus for life). This is caused by failure of the developing immune system of the foetus to function properly before 110 days.
After birth these calves carry the virus for life and act as a potent source of BVDV infection for in-contact susceptible cattle. Virus infection (not necessarily before 110 days), may also lead to various defects of the developing foetus’ eyes and brain. These calves may be born blind and lack co-ordination, respectively. These calves should be culled for welfare reasons, as well as being a source of infection.
BVD virus during pregnancy may cause:
- Embryonic death and return to oestrus,
- Foetal death/abortion,
- Mummification of the foetus,
- Birth defects of the nervous system and eyes,
- Weak/premature calves,
- Live persistently-infected calves.
Virus infection after 150 days gestation usually has little effect with live calves born at full term.
BVD virus can be spread in semen of persistently infected bulls or in bulls experiencing acute BVD with transient virus infection.
BVD will lead to low pregnancy rate due to embryonic death or later foetal death/abortion. Bulls are vigorously tested for BVD before entering AI studs. Testing for BVDv is essential for all purchased bulls prior to their use on farm.
In older animals acute BVDv infection can reduce milk yield, increase the risk of clinical mastitis and retained foetal membranes, and increase somatic cell counts.
Mucosal disease occurs when persistently infected animals (calves infected before 110 days of pregnancy) become superinfected with cytopathic BVD virus. The cytopathic BVD virus usually arises from changes in the BVD virus within the PI animal. Mucosal disease is most commonly seen in 6 to 12 month-old calves, and is usually seen as sudden onset depression, fever and anorexia, with excess salivation. Ulcers appear in the mouth and on the muzzle. There are purulent discharges from the eyes and nostrils. There is profuse diarrhoea with shreds of gut mucosa/blood present during the terminal stages. There is rapid weight loss followed by death within 5-10 days.
Acute BVD infection:
Paired blood samples 3-4 weeks apart to demonstrate rising antibody levels to this virus.
PI calves may be clinically normal but commonly present as chronic “ill thriven” or stunted calves due to their susceptibility to bacterial infection such as pneumonia. Testing for virus will identify PI calves. Two virus positive samples taken 3-4 weeks apart will confirm persistent infection, but in the vast majority of cases, particularly in ill-thriven calves one positive test is enough. Virus testing can be done via the blood or, particularly in calves < 12 weeks off age, skin (usually a plug of tissue from the ear). Skin testing is useful in younger calves because detection of the virus is not impaired by the presence of antibodies from the colostrum which may be present in the blood.
GENERAL PRINCIPLES OF DISEASE CONTROL
Biosecurity and biocontainment are terms describing programs for infectious disease control.
Biosecurity – reduce/prevent the introduction of new diseases onto an operation from outside sources
Biocontainment – reduce/prevent the movement of infectious diseases on the farm once biosecurity has been breached
Biosecurity is the first measure to prevent introduction of disease onto your farm; biocontainment measures may limit the financial losses following introduction of disease onto your farm after management errors have allowed disease to enter.
Johne’s disease, Bovine Virus Diarrhoea virus (BVDv), salmonellosis, tuberculosis, Leptospirosis, Infectious Bovine Rhinotracheitis (IBR) are some examples of infectious diseases that can be introduced onto your cattle farm and severely affect the financial viability of your beef or dairy cattle enterprise.
Biosecurity is the first measure to prevent introduction of:
- Johne’s disease,
- Bovine Virus Diarrhoea virus (BVDv),
- Infectious Bovine Rhinotracheitis (IBR)
KEY PRINCIPLES OF BIOSECURITY
- Keep a closed herd
- If buying in cattle – only purchase from BVDv accredited herds
- If buying in cattle from non BVDv accredited herds blood test and isolate before introducing to herd
- Prevent contact with cattle on neighbouring farms – double perimeter fence
SALMONELLOSIS IN CATTLE
There are many Salmonella species that are able to infect cattle; some species are also able to infect man (referred to as zoonoses or zoonotic infections), and other farm animals such as dogs and cats. Salmonellosis is more severe in the very young and old in all animal species. Infection can be acquired from contact with faeces, contaminated clothing, aborted material, and un-pasteurised milk. Salmonella species can cause a wide range of clinical signs in cattle including diarrhoea and possible dysentery, joint infections, chronic pneumonia, abortion and sudden death from septicaemia. An outbreak of salmonellosis can have serious economic consequences on a farm as well as public health implications. All bovine abortions, and premature births should be reported to your vet so that the cause can be investigated.
Neonatal calves can present with septicaemia (blood poisoning) which progresses rapidly to death within six to 12 hours. Initially, calves are dull and depressed and do not suck; diarrhoea may be a terminal sign. Ingestion of colostrum from vaccinated dams (2 litres within the first 2-4 hours) is essential to reduce the risk of Salmonella septicaemia.
The clinical signs depend on age and the presence of passively derived immunity (antibodies acquired from colostrum). There is often high morbidity, and mortality may exceed 60%. Commonly, affected calves are dull, anorexic, with an elevated rectal temperature, and have grey pasty faeces with fresh blood and mucus present. Older calves may develop watery foul-smelling dysentery containing mucosal casts particularly associated with S. typhimurium infection causing progressive dehydration and a gaunt appearance. Surviving calves often grow poorly. S. dublin can cause infection of joints and the growth plates of long bones or dry gangrene of the extremities (ears, limbs and tail) after the initial septicaemic episode. Infection of the neck vertebrae causing weakness of all four legs leading to recumbency in two to four month-old calves may be another manifestation of S. dublin infection. The treatment response to all Salmonella infections is generally poor and prevention is much better than treatment.
When abortion, premature birth, stillbirth or the birth of weak non-viable calves occur, the subsequent investigations are likely to include not only the farm’s veterinary practitioner but also an investigating laboratory. Salmonella infection can result in an abortion storm involving up to 25% of cattle at risk therefore it is essential to identify the cause at the start in order to introduce control measures.
S. dublin is the commonest salmonella serotype associated with abortion (80% of salmonella-induced abortions) followed by S. typhimurium. Disease is most commonly associated with the introduction of carrier animals or access to faecal contaminated feed/water supplies. Abortion occurs during 5-8 months of pregnancy, with placental retention followed by poor lactation. Systemic disease is uncommon with S.dublin but likely with S.typhimurium where abortion can follow septicaemia and enteritis.
Isolate aborted cattle for a minimum of five weeks – however infection with S.dublin may lead to a chronic carrier status. Dispose of all products of abortion very carefully. Decontaminate the cow’s environment as far as possible. Consider vaccination of breeding stock where S. dublin is a perennial problem.
Recent evidence suggests that some adult cattle may remain symptomless carriers of S.typhimurium for many months after infection which makes herd control very difficult. A chronic long-term carrier/excretor state is common with S.dublin infection. Prevention and/or control of Salmonellosis are important components of a herd health plan.
Management / biosecurity measures that will reduce the risk of Salmonella infections in cattle include:
- Avoid introducing potentially infected animals by maintaining a closed herd. Quarantine all introduced stock for at least four weeks.
- Source new stock from other farms with high health status and not markets.
- Avoid shared bulls and communal grazing areas.
- Isolate sick animals in dedicated isolation boxes and not calving boxes.
- Clean and disinfect buildings between occupancies. Provide good drainage and waste removal.
- Maintain good fences to prevent straying of neighbouring stock.
- Ensure that milk from ill cows (or cows that have been in contact with such cows) is not fed to calves.
- Protect all feed stores from vermin including birds.
- Only spread slurry on arable land wherever possible. Leave all grazing land at least three weeks after spreading slurry.
- Insist visitors have clean boots and disinfect before entering and leaving the farm premises.
Consider herd vaccination.
Between August and October 2011, outbreaks of disease in adult cattle causing mild to moderate fever, reduced milk yield, loss of appetite, loss of body condition and diarrhoea were reported in both the Netherlands and Germany. Testing for common causes proved negative. From December 2011, abortion and stillbirths associated with foetal abnormalities, affecting mainly sheep but also cattle and goats, were identified in the Netherlands, Germany and Belgium. A new virus was identified in November 2011 as the cause of both conditions. This was named ‘Schmallenberg virus’ (SBV) after the German town where the virus was first identified.
Schmallenberg virus is in the Simbu serogroup of the Orthobunyavirus group. This group of viruses includes many different viruses which occur in Asia, Africa and Australia, but have not previously been identified in Europe. Schmallenberg virus can infect and cause disease in sheep, cattle and goats.
In the Netherlands and Germany outbreaks of SBV disease in cattle have caused clinical signs including fever, reduced milk yield, inappetence, loss of body condition and, diarrhoea. Outbreaks of disease have lasted 2-3 weeks, with individual affected animals recovering over several days. These clinical signs are broadly similar to another midge-borne viral disease – bluetongue.
Clinical signs have not been reported in adult or growing sheep, although there is anecdotal evidence of milk drop in milking sheep in Netherlands.
In newborn animals and foetuses, the disease is associated in animals born alive or dead at term or aborted following infection of the dam, affecting mainly sheep but also cattle and goats. Malformations observed include bent limbs and fixed joints, brain deformities and marked damage to the spinal cord. Persistent flexion of the joints (arthrogryposis or “contracted tendons”) is reported to be a common birth defect. Some animals are born with a normal appearance but have nervous signs such as a ‘dummy’ presentation or blindness, ataxia, recumbency, an inability to suck, and sometimes seizures. The foetal deformities vary depending on when infection occurred during pregnancy.
Malformations affecting lambs exposed to the virus in pregnancy may lead to lambing difficulties. Excessive force must not be used during lambing as this may risk injury to both the ewe and lamb. Farmers should contact their veterinary surgeon because safe delivery may necessitate a caesarean operation. Lambs delivered alive with severe deformities must be euthanased for welfare reasons.
RISK TO HUMANS
At the moment, a Europe-wide risk assessment has concluded that Schmallenberg virus is unlikely to cause illness in people. As yet, no human cases have been detected in any country, and the most closely related viruses only cause animal disease.
THE IMPORTANCE OF THE BULL IN HERD FERTILITY
The influence of the bull on herd fertility in both dairy and beef herds is often overlooked with the focus being on cow infertility. When cow management and infectious disease control are good then the limiting factor in herd fertility may be bull fertility rather than female factors. Infertile bulls (incapable of achieving pregnancies) are rare but studies have shown 20% or more of unselected breeding bulls may be classed as subfertile and thus fail to perform optimally. A fully fertile bull when run with breeding groups of 40-50 cows should be able to achieve average pregnancy rate to each service of 60% meaning in 9 weeks of breeding at least 94% of cows should be pregnant.
Targets for efficient beef herd fertility should be 95% pregnancy rate in a 9-10 week mating period with 65% or more of cows calving in the first 3 weeks of the subsequent calving period. These figures cannot be achieved without a fully fertile bull stud and for this reason all farmers should consider routine examination of their stock bulls as an essential part of herd fertility management. The economic benefits of less barren cows are obvious but what is often overlooked is the financial benefit of calving more cows in the first 3 weeks of the calving period which will significantly increase average weaning weights and financial output. The practice of rotating bulls around breeding groups of 30-40 beef cows for extended mating periods may mask the presence of subfertile bulls on many farms but will lead to ongoing fertility inefficiency.
THE COMPONENTS OF BULL FERTILITY
For a bull to be fully fertile and perform to full potential each of the following components must be considered :
- Libido (sex drive) and physical fitness
- Ability to achieve intromission and deposit semen in the vagina
- Production of sufficient quantities of high quality semen
- Absence of disease that could be transmitted to cows during breeding eg Bovine Virus Diarrhoea (BVDV) or Campylobacter
There are many conditions that can effect the production and quality of semen produced from the testicles. Scrotal circumference gives an indication of adequacy of testicular tissue volume and has a direct relationship with fertility. In addition to circumference it is important to look for bulls with good scrotal conformation. Bulls with tight, wedge shaped scrotums will be less able to regulate the temperature of their testicles and overheating can lead to reduction in semen quality. Bulls should achieve standards for scrotal circumference by certain ages and those that fail to reach these standards are likely to be subfertile due to failure of normal sperm production capacity. Bulls with small testicles will at best produce small quantities of normal semen and at worst may be infertile due to hypoplasia of sperm producing cells. In general bulls should have scrotal circumference of at least 32cm at 18 months of age and 34cm by 24 months of age (individual breed society standards may vary). Infection of testicles (orchitis) can cause infertility and will cause initial swelling and then degeneration (shrinking) of affected testicles. Epididymitis causes swelling and blockage of the ducts that carry sperm form the testicles and may not be obvious unless careful palpation of the testicles is carried out.
Bulls can have temporary degeneration of sperm producing cells in their testicles for a variety of reasons including fever, lameness, stress, toxaemia and this can only be detected by collecting and examining a semen sample. Semen can be collected on farm from most bulls by your vet by electro-ejaculation . The motility and percentage of normal sperm cells can be measured indicating the quality of the semen sample .
INFECTIOUS DISEASES AFFECTING FERTILITY
Bulls can carry and transmit various infectious diseases and much of this risk can be avoided by good health planning. Bulls should always be tested clear of BVD virus and vaccinated before use. Bulls from accredited herds may be sold naïve to BVD and are thus susceptible to BVD infection during transit/sale and when entering endemically infected herds. Ideally all breeding bulls should be vaccinated for BVD before sale and in herds where IBR and Leptospirosis are a risk then the bull should be vaccinated before mixing with the herd. It is easy to forget the bull during annual herd vaccination programmes but this can lead to temporary infertility if the bull is exposed to disease during the breeding period. Use of hired or shared bulls carries the risk of introducing venereal Campylobacter infection which can have devastating consequences.
THE CALF’S ENVIRONMENT BACKGROUND
Regardless of the type and age of cattle or type of housing (cubicles, straw yards, pens or hutches) the accommodation must provide for the animal’s most basic needs if animal performance is to be maximised and welfare standards met. Air space is just as crucial as floor area. Pneumonia is especially common in housed animals and the disease can often be avoided if buildings are not overcrowded, are well ventilated and well drained, and animals of different age groups are not mixed together.
With dairy units it is not uncommon for young stock to be housed in cubicles, although straw yards are more common in beef units. There are advantages and disadvantages with both housing systems, but if the adult cow is being housed in cubicles then there may be advantages to housing the heifer replacements in suitably sized cubicles.
Regardless of regulations or quality assurance schemes, calves require a clean, dry bed in well ventilated but draught free (<2m/sec) conditions. They can be housed individually or in groups. Calf pens should be large enough to allow calves to groom themselves, lie down and stretch their limbs and rise without any difficulty and must allow visual and tactile contact with animals in adjoining pens/hutches. Therefore pen divisions must be perforated, i.e. allow calves to see and touch one another. Calves must be group housed from 8 weeks of age, unless an animal is kept in isolation on the advice of the veterinary surgeon.
Whether they are housed individually or in groups calves require a clean, dry bed in well ventilated but draught free conditions
No more than 12 calves are recommended in any one group; sick calves can be easily identified and treated when they are in small groups. There should be no more than 30 calves sharing the same air space and they should not share that space with older cattle. Air space is critical; with a minimum of 6m3 air space per calf at birth which increases to 10m3 by 2 months of age and then at least 15m3 by 6-7 months. The greater the number of calves in a single air space, the greater is the risk to health. A calf with respiratory disease can shed millions of infectious organisms from its lungs into the atmosphere.
Calf hutches provide suitable housing for either individual calves or the larger hutches can accommodate up to 5 calves. Each hutch must have an outside run for the calves to move around and be in fresh air. The hutches should be situated on either free draining concrete or on a porous (e.g. chalk) base ensuring that any effluent goes to a suitable site for disposal. Plenty of clean, dry bedding (normally straw) needs to be provided which should be disposed of after each batch of calves. Ideally the hutches should be moved after each batch of calves to minimise disease risks.
Cattle are homeothermic animals and need to maintain a constant body temperature around 38º C. The Lower Critical Temperature (LCT) is the temperature below which an animal must burn extra energy to keep warm, i.e. feed is channelled away from growth/production to keeping warm. At temperatures above the Upper Critical Temperature (UCT), cattle will sweat in an attempt to dispel the excess heat and the animal will become heat stressed, which can lead to death of the animal. As cattle sweat at only 10% of the human rate they are much more susceptible to heat stress.
The body temperature can be affected by air temperature, radiant temperature, wind speed and relative humidity together with animal factors such as size of animal, coat thickness, feed level and type, body condition, etc. A newborn calf needs to be kept in a temperature of no less than 7ºC if it is not to suffer. By one month of age a calf can comfortably withstand temperatures around freezing point. It is important though that calves are kept out of draughts, as this increases the LCT quite considerably. However, rarely are low temperatures a problem in Irish conditions with housed animals, quite the converse with the main issue relating to high temperatures and humidity within a building.
At grazing, the story is different due to the compounding effects of rain and wind. Rain in particular can lead to serious mortality rates at grazing, if some form of protection is not offered to young calves. With the calf at its LCT, just 0.10inch rain can increase calf mortality by 2-4%. The rates are even higher in calves that have not received adequate amounts of colostrum.
Dust and gas can have adverse affects on the health of the calf and young animal which extend through to lactation and slaughter. Not only does dust irritate the respiratory tract and mucous membranes it leads to permanent damage to the lungs and encourages micro-organisms. Ammonia at levels of 25ppm will irritate the mucous membranes and also make the animal more vulnerable to respiratory diseases. Studies show that ammonia levels in the first 4 months of life severely impact on the age at first calving. Although carbon dioxide is not poisonous at levels above 3000ppm it adversely affects cattle due to less oxygen being present. Hydrogen sulphide is highly toxic with levels above 50ppm known to kill cattle – the main cause of this problem being agitation to below ground slurry stores.
Not only is air space critical but so is the ventilation rate, which is the amount of air replaced within a building in a given time. The aim is a minimum air change within a building of 10 times each hour, increasing in the summer up to around 60 air changes per hour. The purpose is to keep the air fresh. Studies from the USA show that higher humidity and mean temperatures within the calf housing results in a delayed first calving. It is probable that this would also appear as slower live weight gains in fattening cattle.
In the housed environment a constant supply of fresh air is essential in preventing respiratory and other diseases together with improving production. Good ventilation removes stale, damp air which helps ensure that viruses and bacteria cannot survive for long outside the animal. Ventilation should never be restricted in an attempt to raise air temperature. In the vast majority of situations natural ventilation is adequate. However, if artificial (fan) ventilation is required then it must only be controlled manually or by humidity sensors, never by a thermostat.
Almost all infection occurs by direct aerosol spread between calves, so it is vital that there is good ventilation to allow for removal of infectious organisms. Similarly an increase in humidity will favour viral/bacterial survival.
With climate change a real issue and the increased risk of heat stress in all ages of cattle consideration will need to be given to the installation of fans, combined with spraying water onto the cattle. This can dramatically reduce the effects of heat stress.
Natural ventilation is the most efficient and least expensive system for providing an optimum environment within a building. The objective of the ventilation system must be to provide a continuous stream of fresh air to every housed animal at all times of the day or night. Buildings will naturally ventilate best when they are sited at right angles to the prevailing wind direction.
To ensure adequate ventilation, it is important that the building is designed to:
- Remove excess heat;
- Remove excess water vapour;
- Remove micro-organisms, dust and gases;
- Provide a uniform distribution of air;
- Provide correct air speed for stock.
In Ireland, wind speed is above 1m/sec for more than 95% of the time. This means that for the majority of time, there is sufficient generating force to provide the necessary air changes within a correctly designed building by natural ventilation. For the remaining time, the building relies on the stack effect to replace foul air with fresh air.
Heat produced by the livestock naturally rises. If it is unable to escape from the building at the highest point (at the ridge), it will condense and remain within the building raising the humidity levels. As the air cools, it will fall back onto the bedding, increasing the moisture content and creating a suitable environment for bacteria to flourish. At a relative humidity above 75% pathogens and viruses can survive for several minutes which increase their spread from animals to animal. However at RH levels below 75% viruses die very quickly after exhalation. With many calf houses the humidity is such that viruses can survive for around 40 minutes creating a reservoir of infection in the air which means the disease is rapidly spread.
Natural ventilation requires the right balance of inlets and outlets. If the warm air is able to exhaust from the ridge of the building, this draws fresh air into the building through the side inlets. This air change ensures the stack effect is maintained. The inlet and outlet areas should be about 0.05m² and 0.04m² per calf respectively, with the outlet being at least 1.5m above the ventilation inlet.
The pitch of the roof can influence how well the stack effect is established. A roof profile of 1:4 and 1:3 are ideal. However, the pitch of a roof will always be a compromise between ventilation and overall ridge height, especially with span buildings. It is essential that there are adequate outlets in the ridge of the building. An open ridge is generally between 0.3-0.4m wide and should be un-restricted. As a useful rule of thumb, there should be 5cm of ridge opening for every 3.0m of building width. Although cranked open ridges are still commonly fitted, they only offer around 20% of the required outlet.
The design of a successful natural ventilation system is complex and requires account to be taken of the span of the building, the location of the building relative to other buildings or obstructions (buildings and trees disrupt airflows for a distance of 5-10 times their height), the pitch of the roof, the stocking rate, mass of each animal and the bedding system.
During the main/conventional housing period mechanical ventilation may be required in some calf buildings due to design constraints but should be the last option. However, with summer housed animals this may be essential to minimise the effects of heat stress.
During the summer months fans assist air movement to provide a cooling effect and so increase heat loss from animals.
There are relatively few buildings, which cannot be made to ventilate naturally if they are designed carefully, or remedial works undertaken. The decision to resort to assisted ventilation, with the resulting running costs and maintenance should not be taken lightly. In addition, where mechanical ventilation is essential then fail-safe systems and alarms are a necessity.
The quality of cereal straw varies from year to year, but with alternative uses its price is also becoming a serious issue – even in the cereal growing areas of the country. Efficient use of bedding is therefore of the essence but care must be taken to ensure that cattle cleanliness and welfare are not compromised.
Other bedding materials include sand, sawdust/shavings, bark peelings, waste paper and gypsum waste. Studies of various materials by the University of Arkansas found no significant differences in output of calves housed over a 6 week period on different materials, although straw and wood shavings provided more warmth and absorbency compared to products like sand. However, no cleaning out of pens was done in the trial period which would be uncommon in practice on sand based systems.
- Most calves are housed in less than adequate conditions
- Ventilation is critical
- The more humid the environment the greater the risk of spread of disease from calf to calf
- Calves weighing up to 100kg must have at least 1.5m2 of space – greater is better
- Calves may only be kept in pens for the first 8 weeks of life and must be able to touch and see their neighbours. Thereafter they must be grouped housed
- Calves must be have a dry and comfortable bed to lay on
Disease is best prevented by a combination of good management, appropriate building design and ventilation, and effective vaccination against the major pathogens on that particular unit well before the risk period. The selection of an effective vaccination strategy will form an important part of the herd health plan drawn up in conjunction with the farmer’s veterinary surgeon
Important predisposing viral causes are:
- Infectious bovine rhinotracheitis (IBR)
- Bovine respiratory syncytial virus (BRSV);
- Parainfluenza-3 virus (PI3)
- Bovine virus diarrhoea virus(BVD) may be involved in some herds.
The important bacterial causes of respiratory disease are:
- Mannheimia haemolytica
- Pasteurella multocida.
- Haemophilus somni
The first two organisms are often still collectively termed “pasteurellae” and the disease “pasteurellosis”.
An accurate diagnosis of the cause(s) of respiratory disease is essential so that the correct treatments are given and that steps can be taken to prevent future disease using appropriate vaccines. Antibiotic selection is very important and will be carefully considered by your veterinary surgeon.
Laboratory confirmation may be necessary before embarking upon a vaccination protocol in the face of infection, and to prevent a similar problem during the following year. Diagnosis of viral infection may involve taking ocular and nasal swabs, collection of lung fluid (broncho-alveolar lavage); and for future control measures, collection of blood samples two weeks apart. Post mortem examination is only useful in cases of sudden death. Necropsy of chronic pneumonia cases is largely a waste of money and rarely provides meaningful data.
Secondary bacterial invasion of the damaged respiratory tract frequently occurs which makes treatment difficult. In many situations selection of cattle for treatment based upon raised rectal temperature is the most cost-effective practice (Figs7-8). All rectal temperatures and treatments are recorded and checked the following day to monitor progress.
The choice of antibiotic treatment is based upon veterinary advice and knowledge of previous outbreaks of respiratory disease on the unit. Recurrence of bacterial infections is common (up to 25 per cent) often necessitating repeat antibiotic treatments 5-14 days later. It is very important to recognise that this situation is not caused by antibiotic treatment failure but re-infection of the physically compromised respiratory tract once antibiotic levels have fallen below effective concentrations after several days. It is important to recognise this fact and not blame the manufacturer of the antibiotic or the veterinary surgeon who recommended its use.
While antibiotic treatment of the whole group of calves is practised in some situations this often results in a doubling of treatment costs because up to half the calves are injected unnecessarily because they would not have succumbed to disease. In most respiratory disease outbreaks whole group antibiotic treatment is undertaken for labour reasons and convenience, and is not based upon veterinary evidence.
INFECTIOUS BOVINE RHINOTRACHEITIS (IBR)
Disease typically affects store cattle infected at the time of purchase from markets but clinical signs generally first appear 2-3 weeks following housing.
When first recognised in Ireland during the late 1970s in its most severe form the morbidity rate (percentage of cattle affected) could be 100% with up to 5% deaths. The first two or three cattle to show clinical signs are invariably the worst affected.
Affected animals do not eat, are very depressed, slow to rise, and stand with the head held lowered. There is a purulent discharge from the eyes and nostrils.
Treatment is based upon veterinary advice and it is essential that the vet is contacted as soon as disease is suspected because the first cattle affected are the most severely affected and accurate diagnosis, treatment, and timely vaccination are essential to prevent further losses.
Disease is best prevented by vaccinating all purchased cattle as soon as they arrive on the farm and turning them out to pasture for several weeks whenever possible.
Maintenance of disease-free status is possible for closed beef herds but virus can be transmitted by direct contact over fences etc. from neighbouring farms. Annual vaccination of all cattle on the farm is a valuable insurance policy against disease.
The clinical signs attributable to BRSV infection are highly variable. In severe outbreaks some animals may be found in respiratory distress with mouth- breathing and rapid abdominal movements leading rapidly to death. In some studies involving housed beef calves infection has occurred without any clinical signs of respiratory disease. In these situations exposure to the virus is detected by measuring serum antibody concentrations and recording significant rises.
There are a number of vaccines widely used to control BRSV-induced respiratory disease and veterinary advice should be sought for the most appropriate prevention strategy. Vaccine can be administered intra-muscularly on two occasions, four weeks apart, prior to the anticipated challenge (e.g.housing) although the second vaccine is often administered at housing. Single intranasal vaccination may be as effective as two intramuscular injections and may be effective in the face of a BRSV-induced respiratory disease outbreak.
General control of respiratory disease
Control of respiratory disease is likely to be best achieved by attention to general husbandry practices especially the ventilation system which can often be greatly improved on most farms, and correctly-timed administration of vaccines.
Reducing stocking density, wherever possible, would improve the respiratory disease situation on most units. Stressful events such as disbudding, dehorning and castration are best undertaken before housing or delayed until calves have been housed for at least six weeks.
Details of these control measures must be included in the veterinary herd health plan. Expert advice on ventilation of buildings may be necessary.
Main points of building design:
- Air enters below the eaves and exits at the ridge (natural or stack effect whereby spent warm air rises to the ridge out to be replaced by fresh air drawn in from below the eaves)
- Minimum of 6 air changes per hour on a still day Air should appear fresh and free of ammonia or slurry smells when you walk through the shed especially during still winter nights
- The ridge opening should be 300 mm (minimum) with a cap at least 150 mm above
- Buildings should not exceed 20m width. Multispan buildings should be avoided
- Minimum airspace allowances 10 cubic metres for calves up to 90 kgs
- Upturned corrugated sheeting on roof with a 25 mm gap
- Spaced boarding all round building including gable ends
- Ensure adequate drainage to prevent high humidity. Condensation on underside of roof and cobwebs over outlets are indicators of poor ventilation.
COCCIDIOSIS IN CATTLE
Coccidiosis is caused by infection by protozoan parasites called Eimeria spp. which parasitize the lining of the intestinal tract. E. zuernii, E. bovis and E. alabamensis are the most common and pathogenic. Infection causes a loss of absorptive capacity of the gut with consequent diarrhoea and possibly dysentery. Outbreaks of disease are commonly seen 3-4 weeks after mixing groups of dairy calves.
In severe clinical coccidiosis there is sudden onset of profuse foetid diarrhoea containing mucus and flecks of fresh blood with staining of the perineum and tail. Straining with partial eversion of the rectum may occur in severe cases. Affected animals do not have an elevated rectal temperature but their appetite is greatly reduced and they develop a gaunt appearance.
More usually, chronic wasting and poor appetite are the presenting signs. Morbidity is high but mortality, even in severe cases, is low. Convalescence is protracted in all cases causing financial losses due to poor weight gains.
Veterinary diagnosis is based upon typical clinical findings affecting a large number of calves in the group. Interpretation of faecal examinations is not simple because there are low numbers of oocysts present in the faeces of many normal calves. The stage of infestation also greatly influences the number of oocysts present in faeces. So the demonstration of large numbers oocysts in faecal samples is helpful but speciation to determine whether they are pathogenic (capable of causing disease) is rarely undertaken in field outbreaks. There is a good response to specific anticoccidial therapy.
Histopathology findings of coccidiosis in the gut of a dead calf confirms the clinical diagnosis.
It is very important to move calves from infected pastures/premises immediately. Toltrazuril and diclazuril can be used for both treatment and prophylaxis of coccidiosis. Sulpha drugs given orally for three to five days is the standard treatment. Oral fluid therapy may be indicated in certain cases.
Straining with passage of only mucus. Partial eversion of the rectum may occur in severe cases.
- Strict attention to disinfection of buildings between batches of calves and clean feeding areas mean that coccidiosis is uncommon in modern dairy units.
- Decoquinate can be used in-feed for prevention of coccidiosis in diary calves and Vecoxan can also be used as a Preventative but timing is crucial. Contact your vet for advice.
- Disease in beef calves may result from contaminated water courses in pastured cattle during summer months where there is no other supply. Fence off all surface water wherever possible.
- As survival of oocysts is possible from one year to another – calving on the same pasture each year may increase the risk of coccidiosis.
- Weight loss and protracted convalescence may result in lower weaning weights in beef calves. Gathering calves for treatment, plus medicines, also adds to the costs of disease.
Recent surveys have revealed that more than two-thirds of dairy calves do not receive adequate volumes of good quality colostrum within 12 hours of birth. If calf diarrhoea, joint infections, meningitis, and septicaemia have become a problem in young calves on your farm it would prove very worthwhile to check their immune status by means of a simple and inexpensive blood test (measurement of total plasma protein concentration) undertaken by your veterinary surgeon.
Delayed colostrum ingestion may result from, recumbency of the dam caused by dystocia, trauma, nerve damage, and milk fever. Unlike many beef cows, summer mastitis should not be a problem in dairy cows but pendulous udders and distended teats may delay sucking. Prolonged labour and nerve damage may cause delays in the calf rising to its feet and sucking normally.
Heifers generally produce colostrum with 25 per cent less immunoglobulin content (protective antibodies) than mature cows so a proportionally greater quantity should be fed to their calves.
The level of hygiene in most calving boxes in seasonally-calving herds could be improved on almost all farms by more regular mucking out, disinfection, and plenty of dry barley straw bedding. Not only would a higher standard of hygiene result in fewer calf diseases, it may also reduce the risks of coliform mastitis and uterine infection in the dam. While firm footing is important in calving boxes because of the risks associated with cows slipping, especially when suffering from milk fever, there is the tendency to over-compensate and not clean out calving boxes for several weeks. Navel dressing with strong veterinary iodine BP is essential at birth and again two to four hours later to prevent navel ill.
Individual calf pens
Wet, dirty or inadequate bedding allows a build up of pathogens in calf pens. Survival of most gastrointestinal pathogens and maturation of coccidial oocysts is best under moist, cool or warm conditions. Some infectious agents (particularly protozoa causing coccidiosis) survive for many months, even after routine cleaning. Poor hygiene with respect to feeding equipment (e.g. dirty buckets and contaminated water drinkers) constitutes an important source of infection not only for pathogens causing diarrhoea but diseases such as calf diphtheria.
Calf hutches provide good accommodation with respect to the prevention of respiratory diseases but must be cleaned out and disinfected between occupants to prevent a build-up of enteric pathogens (see above with reference to calf pens). Movement of calf hutches between calves is an effective means of providing a clean surface.
FEEDING ARTIFICIAL MILK REPLACERS
Artificial milk replacers prepared at the wrong temperature or concentration, and raw milk fed at different temperatures may cause nutritional scour. Scour in calves may also occur if animals are fed at irregular intervals or if there is a period of enforced starvation followed by greedy feeding. Fresh clean water must always be available because thirsty calves (e.g. during hot weather or after transport) may drink too much milk, resulting in nutritional scour.
Paratuberculosis can be transmitted to newborn calves if colostrum from infected cows is fed to young calves. As a general guide colostrum must only be fed to the offspring of that cow. Pooling colostrum from numerous cows only adds to the potential spread of disease.
Infectious causes of diarrhoea
Rotavirus infection is a common cause of diarrhoea in young dairy calves. Calves are most commonly affected at 8 to 14 days old when there is an acute onset of diarrhoea with the passage of very watery yellow/green faeces. Infection may be acquired in the calving accommodation then spread between young calves in the calf house by direct contact. Typical early signs include a reluctance to stand and drink, mild depression and salivation. The calf becomes dehydrated with sunken eyes and tight and inelastic skin; recumbency soon follows.
The diarrhoeic calf should be isolated in a dry, well-bedded pen. 1-2 litres of oral electrolyte are given 4 to 8 times daily. Intravenous fluids administered by a veterinary surgeon are essential in dehydrated calves that are unable to stand unaided.
Oral antibiotics are generally not necessary. Parenteral antibiotics should be used to control concurrent infections, e.g. navel ill and calf diphtheria. Milk should not be diluted with electrolyte solution. Alternate milk and electrolyte solution should be fed every four hours.
Annual vaccination of the dam with a combined rotavirus, coronavirus and K99 combined vaccine will prevent disease in the newborn calf following colostrum feeding for the first two weeks of life, and is an invaluable insurance policy in dairy herds.
Since protection of calves depends on the physical presence of passively acquired antibodies within the gut, calves must receive adequate colostrum from their dams. In the dairy herd, colostrum from the first six to eight milkings of vaccinated cows should be pooled and retained in a cool place. The calves should then be fed on this pool at the rate of 3 to 4 litres per day (according to body size) for at least the first two weeks of life. Optimal results will be obtained if a whole herd cow vaccination policy is adopted. This will ensure that the level of infection and consequent virus excretion is kept to a minimum and consequently, the overall level of disease challenge on the farm is kept to a minimum.
Outbreaks of calf coronavirus diarrhoea are similar to, or more severe than, those observed for rotavirus infection. Fortunately, coronavirus infection is much less common than rotavirus.
Treatment and prevention of coronavirus infection is as outlined above for rotavirus.
ENTEROTOXIGENIC E. COLI
In calves this term is used to refer to strains of the bacterium E. coli possessing the K99 antigen. Recent surveys show the incidence of K99 E. coli to be very low in dairy herds. The disease characteristically affects calves aged 1-3 days old when there is sudden onset of profuse yellow/white diarrhoea causing rapid and severe dehydration. The calf quickly becomes recumbent. Accumulation of fluid in the abomasum and intestines gives the abdomen a bloated appearance. Disease would typically follow introduction of infection into the herd with contamination of the calving environment and infection of newborn calves.
Prevention of Enterotoxigenic E. coli infection is as outlined above for rotavirus and coronavirus using a combined vaccine and ensuring passive antibody transfer in colostrum.
Cryptosporidiosis is not a major problem in dairy calves housed in individual pens but infection can rapidly build-up in group pens fed by automatic feeders where newborn calves are constantly added to the group.
Diarrhoea is caused by the physical loss of absorptive area of the small intestine and exacerbates the viral infections described above. There is profuse yellow/green diarrhoea with much mucus present. There is only mild dehydration but the calf rapidly looses condition over 2-5 days and has a dull tucked-up appearance. Whilst morbidity is high, the mortality rate in uncomplicated cases is usually low.
In uncomplicated cases ensure that the scouring calf is properly hydrated and use oral electrolyte solutions as necessary. Halofuginone lactate has recently been licensed for the prevention and treatment of diarrhoea caused by C. parvum. Cryptosporidiosis is a zoonotic disease (can affect man). Children and the elderly are most at risk when handling calves, less so contaminated boots/clothing and other indirect sources of infection.
Salmonella species, such as Salmonella Dublin and Salmonella typhimurium, can cause severe diarrhoea with the presence of blood and mucosal casts which may result in death. More often, Salmonella infections of young calves cause joint and bone infections and severe pneumonia which proves very difficult to treat. Identification of Salmonella infections necessitates detailed veterinary investigation.
Prevention and control of calf diseases caused by certain Salmonella spp. can be achieved by appropriate vaccination of the dam with colostral transfer of protective antibodies.
JOHNE’S DISEASE (PARATUBERCULOSIS)
Johnes’s disease (Paratuberculosis) is a chronic enteritis of adult cattle and sheep caused by Mycobacterium avium subspecies paratuberculosis (MAP). The main signs in cattle are progressive weight loss and chronic diarrhoea. Diagnosis and control are difficult. If your herd has no history of Johne’s disease it is critical that all measures are taken to prevent introduction of infection because eradication of disease once prevalent in the herd proves very costly and may take many years.
There is limited but disputed evidence that the organism may be associated with Crohn’s disease in humans.
The disease occurs worldwide, but especially in temperate climates, and affects particularly cattle, sheep, goats and deer reared in intensive systems. Many wildlife, including rabbits, and exotic species are also susceptible to Johne’s disease.
There is evidence for intrauterine infection of the developing calf in the case of heavily-infected dams. The disease is also transmitted to young calves by ingestion of the organism in colostrum, and from the faeces of infected animals contaminating food and surface water/water troughs, and the cow’s teats. There is a long incubation period and clinical disease is not usually apparent until three to five years-old although younger cases are possible. Infected animals may shed organisms in the faeces for over a year before clinical signs appear.
Early Clinical Signs
Farmers should look for diarrhoea, poor milk yield and weight loss in cattle three to five years-old with onset often following calving or other stressful event (sale, transportation etc). There is no fever and the animal maintains a good appetite until the terminal stages. Clinical signs may continue for several months with the cow/bull becoming emaciated, and then being culled for economic/welfare reasons.
Control and Prevention
There is no single reliable test for confirming Johne’s disease during the early stages of disease (test described as having a low sensitivity).
Blood tests detect antibodies to crude M.paratuberculosis antigen but not all cases have a detectable antibody response. In practical terms diagnosis is best done using a combination of serology (blood tests) and faecal examination for the causative organism.
Control is difficult because of the long incubation period, shedding of infection by animals before they show clinical signs, and diagnostic techniques with poor detection rates in the early stages of disease.
Eradication requires a substantial commitment by the farmer, veterinarian and local laboratory and is based upon the identification and removal of infected animals. Blood testing and/or faecal examination may be done every 6-12 months with slaughter of positive cases. Two consecutive herd negatives may indicate eradication.
Practical control measures that can readily be adopted to limit losses in a diseased herd include:
- Rapid culling of diseased animals.
- Minimise faecal contamination of food, water and pasture e.g. by raising feed and water troughs, strip grazing, use of mains/piped water rather than surface/pond water, avoiding spreading yard manure on pasture, and maintaining good hygiene in buildings/yards and calving boxes in particular.
- Separate newborn calves from dams at birth and rear by bucket with artificial colostrum/milk (only possible for dairy calves).
- Do not feed waste milk to calves
- Do not raise calves from known infected dams as breeding replacements.
- Re-stock only from accredited herds especially bulls.
There is no effective treatment and animals must be culled as soon as the diagnosis is confirmed. It would be prudent not to keep the progeny of infected cows as breeding replacements. Such offspring will generally fatten normally as clinical disease is unusual before year two.
General Recommendations for Veterinary Surgeons
Determine which of the herds in your practice has cows with Johne’s disease. If the herd is found not to be infected, discuss with your clients the merits of joining a national herd test-negative Johne’s disease program/scheme.
Emphasize the importance of biosecurity measures to help prevent your clients’ herds becoming infected though purchase of cattle.
- Keep clinical cases and Johne’s test-positive cows out of the calving accommodation/pens.
- Clean the calving accommodation/pens often.
- Remove the calf from the calving accommodation/pens within one hour after birth.
- Feed each calf four litres of colostrum before the calf is 6 hour-old.
- Cow’s teats should be prepped before colostrum collection to limit faecal contamination.
- Colostrum should be fed from one test-negative cow to one calf. The cow that donated the colostrum should be recorded on the calf’s health record card.
- After colostrum, feed only milk replacer or on-farm pasteurized milk.
- Rear calves well away from adult cattle ensuring no contact with slurry or contamination of water or feed with faeces/slurry.
High cell counts cost money. The cost of a high cell count doesn’t just come from the penalties imposed or bonuses foregone when targets are not met; high cell count cows produce less milk than low cell count cows. A high cell count herd will also have more clinical mastitis. So reducing cell count can provide substantial benefits – on average, reducing the bulk cell count from 250,000 to 150,000 will result in increased earnings of around €40 per cow per year, most of which comes from an increase in production of around 0.5L more of milk per day. So cell counts are a valuable tool which can be used to identify a problem, assess the cost of the problem, give a guide as to the solution, and to monitor the response to control programmes.
WHAT IS A SOMATIC CELL COUNT (SCC)?
Just like any other organ, when the udder is infected somatic cells from the blood (white blood cells) move to the udder and into the milk to defend the organ against the invading bacteria. Without this response, elimination of mastitis, even mild cases, would be very slow and tissue damage greatly increased.
The stimulus for this invasion is tissue damage. This releases a range of chemicals including some which attract the white blood cells to the damaged tissue and some which activate them. The white cells then attack and attempt to destroy the invading bacteria. Most commonly, the white blood cells envelop the bacteria and internalise them. They then attempt to digest the bacteria using enzymes.
Somatic cell counts simply measure the number of cells in the milk; the higher the somatic cell count the greater the chance that the udder or quarter is infected. Uninfected cows and quarters often have a milk SCC of <100 000/ml, and almost always have a SCC <200 000. The same applies to bulk milk SCC – on average, the higher it is the higher the proportion of infected cows in the milking herd. With good mastitis control, the bulk milk SCC should be below 200 000.
CAN CELL COUNTS BE TOO LOW?
For an individual cow the ideal cell count is 100 – 150,000. Below 50,000, there is some evidence that cows respond more slowly to infection, particularly with E. coli, so they have an increased risk of mastitis. So as reducing bulk milk below 100/150,000 may increase the proportion of very low cell count cows, it may also increase the risk of clinical mastitis. Nevertheless because of the other benefits of low bulk cell count the answer is not to increase cell count but to maximise immunity (such as by minimising negative energy balance) and to keep the cows in as good an environment as possible.
DETECTING HIGH CELL COUNTS
Changes in bulk milk SCC reflect changes in the underlying cell count of the milking herd, so bulk milk SCC can be used as an early warning system to identify increases in the number of infected cows. Over the long term, bulk milk SCC can also be used to detect seasonal trends in cell count, which can be useful in identifying mastitis risk factors However, bulk milk SCC is a fairly crude and unresponsive measure. Often by the time that bulk milk SCC has risen there has been a significant increase in the proportion of infected cattle. Bulk milk SCC also underestimates the average SCC of the milking herd – partly because high cell count cows are often excluded from the bulk tank but also because the two measures are not the same. Furthermore, because it’s a bulk measure it provides very little data on the number of infected cows and the dynamics of mastitis in the herd. Individual cow SCC is a much more valuable measure. Regular measurement of individual cell count at herd testing can provide data on the proportion of infected cows, which cows are infected, how long they stay infected for, the rate at which new infections are occurring, and seasonal impacts on those data.
Although regular herd testing is the best method of detecting high cell counts in individual cows, a cheaper alternative, which can also be used in an emergency if a herd test is not available, is the California mastitis test. This is a cow side test which uses the fact that when mixed with a detergent, the DNA in the white blood cells is released. If the cell count is high enough a visible gel will form. The CMT test is performed using a four well paddle as described below
CALIFORNIA MASTITIS TEST
- Discard foremilk
- Squirt milk into wells – one per quarter
- Add equal amount of reagent and mix
- Reaction is scored on a scale of 0 (no change) to 3 (almost solid)
Special reagents are available but recent research has shown that a mixture of 1 to 4 Fairy liquid to water is just as effective, particularly if a few drops of food colouring are added, and much cheaper. Cheaper detergents tend to not be as effective.
One advantage of the CMT over an individual cell count is that all four quarters are tested whereas an individual cell count is a cumulative count of the quarters. This means that 3 normal quarters can mask the effect of an abnormal one – e.g. a cell count of 500 000 in one quarter and 100 in the other three will result in a whole udder cell count of around 200 000. Individual quarter herd tests are cost prohibitive in most situations, so using a CMT on at-risk cows is a useful exercise.
USING CELL COUNT DATA
Individual cell counts tell you what the current infection status of the cow is likely to be. However a single figure on its own is of limited value. Firstly there is the masking problem discussed above. Secondly, the most obvious cows on a single herd test are those with the highest SCCs. These cows are likely to have long established infections that which will not respond well to treatment. These cows need to be managed to reduce the risk they pose to the rest of the herd, by techniques such as culling, early drying off or milking separately, but the time has long past for simple identification and treatment. The more important cows are those with persistent infection but lower cell counts; early detection and treatment of these cows is likely to have the most benefit. The best use of SCC is as a dynamic test with multiple results per cow; this will allow early identification of persistent rises in cell counts in cows to < 400 000.
Working with your vet, you can use your routine herd test to identify what the underlying cell count problem is, what the main risk periods are and what are likely to be the best solutions for your herd. Herd testing provides individualised data to be used in an individualised herd health plan.
- High somatic cell counts, either bulk or individual, mean money is being lost.
- When a cow has mastitis, white blood cells move to the udder to defend it. It is this movement of white blood cells which causes the rise in cell count.
- Effective mastitis control should keep bulk milk and individual cell counts < 200 000
- Bulk milk cell counts are available from routine test and provide useful data, but for effective control monthly herd testing of individual cows is required
- The California milk test is a cheap, but time consuming alternative to herd testing, that is best saved for individual cows or emergencies
- The use of computer programmes has revolutionised the value of herd testing. they can quickly identify trends in cell count and identify target areas for mastitis control
Neosporosis is caused by infection with the protozoa Neospora caninum. Neosporas been found world-wide and in many species other than cattle. Currently abortion due to Neospora has been shown in cattle, sheep and horses. The dog and other canids (such as foxes) are the definitive host. That is they are the animals in which the parasite becomes sexually mature and reproduces.
- Abortion, between 3 and 9 months of pregnancy (particularly 5 to 7 months)
- Still birth or premature calf
- Occasionally, calves will have brain disease at birth
- No other signs seen in the mother
- Repeat abortions possible in the same cow.
- Clinical signs of little help
- Characteristic heart and brain damage in aborted calf
- Identification of parasite in the calf tissue
- Antibodies in the mother’s blood
However, as a large number of healthy calves can be infected with Neospora it is important to eliminate other causes of abortion, particularly BVD or leptospirosis before a diagnosis of neosporosis is made
No treatment of any proven benefit
Dogs are potentially a source of disease. So prevention must include:
a) Keeping cattle food and water away from dogs and foxes
b) High hygiene standards at calving. Dispose of placental membranes and aborted or dead calves before dogs can get them
However, transmission from mother to calf (known as vertical transmission) is far more important. Over 90% of calves born to mothers with antibodies to Neospora will have been infected in the womb. The importance of transmission between cattle is less clear. Nevertheless, vertical transmission alone can maintain infection in a herd. To eliminate Neospora you need to:
Identify infected cattle and cull them: All cattle with antibodies to Neospora are sources of infection to their calves. Additionally cattle with antibodies are 20 times more likely to abort between 90 and 270 days of pregnancy than cattle without antibodies. Finally, on average, infected cows produce less milk than antibody negative cows.
Select only seronegative cattle for breeding. Heifers with antibodies should be sold for meat not bred.
These strategies look expensive to achieve, however the cost of neosporosis far outweighs the cost of eliminating it from the herd
Teat disinfection is the cornerstone of all mastitis control programmes. Disinfecting the teats after milking (post-milking teat dipping / spraying) is one of the key planks of the 5-point plan introduced in the 1960s and, since then, has been shown to be effective in a huge number of studies. Pre-milking disinfection has not been in use for so long, but is now commonly seen on-farm.
There are two commonly used methods of teat disinfection – either dipping each teat separately using a cup filled with disinfectant or by spraying disinfectant onto the teats from below. Whichever method is used, the full benefit of teat disinfection will only be achieved if the disinfectant is applied efficiently and effectively. The two main factors inhibiting the effectiveness of teat disinfection are ineffective formulation and poor application. Problems with product formulation are usually due to either incorrect mixing of concentrate on farm, or to extraneous water getting into a previously prepared mixture. Poor application, i.e. failure to cover the whole teat of every cow at every milking is the most common error in teat disinfection. All the benefits of correct product selection, preparation and handling are lost if the teat disinfectant does not reach the skin of the teat. Proper disinfection is not just disinfecting the teat end but disinfecting the entire teat barrel – that is, everywhere the liner has touched. However, there is no benefit to be gained in disinfecting any other part of the udder surface. Teat dipping is the best method of disinfection, but spraying can be just as effective, if it is carried out conscientiously.
PRE-MILKING TEAT DISINFECTION – WHAT’S THE POINT?
Pre-milking teat disinfection involves applying a quick-acting disinfectant just before milking to reduce the population of mastitis-causing bacteria on teat skin especially in the region of the external teat orifice. The major effect of pre-milking teat disinfection is therefore against those environmental micro-organisms which cause mastitis. Pre-milking disinfection is not aimed at improving teat condition, so the addition of an emollient is not indicated.
Pre-dipping reduces new environmental streptococcal infections and Escherichia coli by as much as 50%. Pre-dipping teats should be considered if there are high numbers of mastitis cases due to environmental bacteria (> 5 per 100 cows per month), or, particularly in spring-calving cows, at high risk periods such as in the first week after calving.
Pre-dip should be applied to teats after they have been fore-milked and then dry-wiped, or washed and dried. Pre-dip needs a minimum contact time of 30 seconds and must be wiped off prior to the application of the milking units. If you are going to pre-dip, ensure that you use a registered product and do not just use your post-milking teat disinfectant. Most post-dips do not have a very rapid speed of action and their use as a pre-dip may contaminate the milk.
POST-MILKING TEAT DISINFECTION – CRUCIAL FOR MASTITIS CONTROL
Post-milking teat disinfection should prevent mastitis and enhance teat skin condition. -In preventing mastitis, the post-milking teat disinfection works by the removal of mastitis-causing bacteria from the teat skin and teat sores. Disinfectant should be applied as soon as the cluster is removed, -while the teat canal is still open. The dip can then penetrate the teat orifice, ensuring that those bacteria which have just entered the canal will also be killed.
The main source of mastitis bacteria on the skin of the teat is the milk from cows with infected quarters. Staph aureus or Strep agalactiae from the milk of an infected cow can remain on the teat cup liners for up to 9 milkings. This means that infection can spread from one cow to the next 9 using the same cluster. Most of the bacteria will be on the teat skin from where they can move into the udder at the next milking. Unless they are removed, bacteria on the skin can multiply (especially at sites of teat lesions) increasing the risk of infection via the teat canal at the next milking. Post-milking teat disinfection, dipping or spraying, removes the bacteria that spread during milking and, as such, is an extremely effective weapon against the spread of contagious mastitis.
Any skin lesion which is infected heals very slowly. Teat disinfection removes bacteria from the skin surface, thus promoting healing. Rough or chapped teat skin can also be a reservoir for mastitis-causing bacteria, so thorough disinfection of the whole teat is important.
Dips can be applied by hand-held cups or with a ‘power dipper’ (a dip cup on a wand with solution applied when a trigger is activated). Dipping uses less product than spraying (approximately 10 ml per cow per milking versus 15 ml, respectively) and, provided that it is carried out correctly, can provide an excellent teat coverage. This application method requires slightly more time than most spraying applications when taking preparation, refilling and actual application into account. Cups should be emptied before refilling, rather than ‘topped up’ when the solution becomes low and any solution remaining at the end of milking should be discarded. The cup should be large enough to accommodate the teat without causing excessive spillage of the disinfectant solution. The act of immersing each teat in a reservoir of disinfectant usually ensures the entire teat barrel (any area in contact with the teat liner) will be covered, as long as the cup is deep enough and filled with the appropriate amount of an effective solution.
Spraying requires more disinfectant than dipping to achieve the same degree of teat cover because spray will also be applied to the udder. Sprays can be applied using a gun-type hand piece with a spray nozzle or a fully automated spray system. Teats should be sprayed from below using a circular motion to cover all sides of all teats. The drawback of spraying is that there is a much greater chance of achieving only partial teat cover than when dipping. The absence of disinfectant on the other side of the teat could allow the establishment of a reservoir of mastitis-causing bacteria. Partly blocked spray nozzles can also result in poor teat cover.
Fully-automated teat disinfectant spray delivery systems are available. Infrared light beams activate spray nozzles and spray patterns are adjusted to the average cow’s udder. Although they can save time and man-power, most automatic units will not give as consistent teat coverage as manual spraying.
TEAT DISINFECTION PRODUCTS
More than 10 different active ingredients have been used in teat disinfectants throughout the world over the past 30 years. The most commonly used active ingredients are: iodine, chlorhexidine, quaternary ammonium compounds, hydrolysed fatty acids, hypochlorite, and acid anionic compounds.
Teat skin has relatively few sebaceous glands and continual washing followed by exposure of damp teats to a cold and windy environment can remove protective fatty acids and lead to cracking. Hence, emollients are added to the disinfectant preparations. The addition of emollients, such as glycerine, sorbitol, lanolin or propylene glycol, to teat disinfectant can improve teat skin health and so reduce the likely reservoir of mastitis bacteria in teat sores and cracks. Many teat disinfectants contain emollients when they are sold. Addition of excessive amounts of any emollient (i.e. >20%) will most probably reduce killing activity and could lead to increases in the new mastitis.
FOR EFFECTIVE TEAT DISINFECTION ALWAYS:
Read the label and follow the instructions on dilution rates, water quality requirements, mixing procedures, shelf life, compatibility information, and storage conditions.
Prepare fresh disinfectant for use (not older than 3 days), and this should be stored in a container with a lid so that extraneous water will not find its way into the already prepared solution thus diluting it.
Regularly clean the equipment (minimum once a week).
Poorly prepared disinfectant applied with dirty and contaminated equipment can be a source of new mastitis infections.
- Teat disinfection is an important measure in mastitis control.
- It can be carried out pre- and post- milking or by a combination approach.
- Pre-milking teat disinfection controls environmental mastitis (i.e. Strep uberis).
- Post-milking teat disinfection controls contagious mastitis (i.e. Staph aureus).
- Teat disinfectants can be applied by dipping or spraying.
- Application by spray can be as effective as dipping when applied properly and consistently.
- Dipping requires less disinfectant, but more time.
- Addition of emollients to the teat disinfecting solution can improve teat skin health.
- Equipment must be regularly cleaned. Otherwise it can act as a source of mastitis bugs.
Skin Conditions in Cattle – Non Parasitic
Photosensitisation occurs either as a primary condition following ingestion of photodynamic agents or secondary to liver damage, resulting in retention of the photosensitising agent phylloerythrin.
Typical cases of photosensitisation affect non-pigmented skin which may ooze serum.
Typical cases of photosensitisation affect the muzzle and non-pigmented skin. The affected skin may ooze serum. During the later stages, the affected skin becomes dry and parchment-like and sloughs off.
During the later stages the affected skin becomes dry and parchment-like and sloughs off.
Affected animals must be removed from pasture and confined in dark buildings to prevent further exposure. Symptomatic treatments include topical antibiotic powders and fly control preparations.
Ringworm is common in young stock and is readily transmitted to humans (zoonosis). The greyish lesions are slightly raised, well-circumscribed, and are more common on the head and neck but may extend over much of the body.
Ringworm lesions are greyish, well-circumscribed, and are more common on the head and neck.
Ringworm is often worse in poorly growing animals.
Spread to other animals in the group..
Diagnosis is based upon demonstration of spores on microscopic examination of plucks of hair surrounding the lesions.
While the disease is often described as self-limiting, resolution may take four to nine months, during which time other in contact animals become infected because of the – contamination of the animals’ environment.
PAPILLOMATOSIS (FIBROPAPILLOMAS, “WARTS”)
Warts are the most common tumours affecting cattle, with most cases seen on the head and dewlap between 6 and 24 months of age. Papillomas may also affect the penis, vagina and teats. The causal virus can be spread by physical contact or equipment such as halters or milking machine. Lesions vary from flat, wide based warts to cauliflower-like growths. Extensive growths that fail to resolve may be seen in immune suppressed animals (e.g. persistent BVDV infection).
Papillomatosis is self limiting and most cases will resolve without treatment in 1-12 months. Owners often request treatment in cases where affected breeding cattle are being prepared for sale, mainly because such animals are unsightly. Autogenous vaccines can be prepared for individual cattle but there are no controlled studies to prove their efficacy.
DERMATOPHILOSIS (BOVINE STREPTOTHRICOSIS)
Dermatophilosis rarely causes significant disease in cattle. Transmission of infection requires wet conditions and close contact. Exceptionally prolonged wet weather during the summer months and those cattle outwintered, produce moist skin that allows penetration of the bacterium and establishment of infection. In Ireland, dermatophilosis is encountered along the dorsum where it causes serum exudation and scab formation at the base of the hairs. The lesions rarely develop clinical significance.
Procaine penicillin injected intramuscularly for three consecutive days effects a cure but it may take several weeks for the scabs to be shed from the growing hair coat.
Penetrating wounds introduce infection through the skin causing cellulitis/abscesses. Failure to observe strict asepsis when administering parenteral injections, particularly of potentially irritant substances, can also cause cellulitis.
Cellulitis lesions can result in severe lameness with painful swelling over the affected area. Cattle are pyrexic and anorexic, with a much reduced milk yield. Large swellings adjacent/involving the legs cause mechanical lameness. In many cases an abscess may not result in illness.