Calf Scour

It has been estimated that 75% of early calf mortality in dairy herds is caused by acute diarrhoea in the pre-weaning period. Diarrhoea is one the most common diseases reported in calves up to 3 months old.

Causes

The occurrence of diarrhoea in calves is a result of the complex interactions of three sets of factors: the calf and the dam, the calf’s environment, including management, and infectious agents. The most important non-specific risk factors for calf diarrhoea are related to disease resistance, level of exposure to infection and feeding.

Disease resistance

The calf is born without any immunoglobulins and an immune system of its own that is very immature at birth. For protection against any infection or challenge from the environment a new-born calf is completely dependent on the ingestion of adequate amounts of good quality colostrum (passive immunity) during the first 24 hours of its life.

Epidemiological studies have shown that many calves do not acquire enough immunoglobulins during the first hours of life. This fact is probably the greatest risk factor for calf diarrhoea during the first weeks of life.

The main reasons for poor transfer of passive immunity from dam to calf are:

• Low levels of immunoglobulins in the dam’s milk, because:
  -the dam has not been dry long enough without calving (minimum 4 weeks);
  -the dam is young (first and second parity cows have significantly fewer immunoglobulins in their colostrum than higher parity cows);
• Inadequate colostrum ingestion (in the study, up to 42% of calves left with their dams for 24 hours failed to suckle adequate amounts of colostrum), because:
  -of the calf (weak calf, difficult calving, inadequate bedding to allow calf to stand without slipping);
  -the dam (poor mothering instinct, difficult calving, no licking, disturbance, tiredness, unable to stand up, poor udder or teat conformation); and
• Inadequate immunoglobulin absorption from the calf’s gut, because:
  -not enough colostrum was ingested early enough (see above; 24 hours after birth no absorption of the immunoglobulins occurs from the gut)
  -there are seasonal differences in the absorption of immunoglobulins (calves born during the summer months in temperate/cold climates achieve higher levels of serum immunoglobulins than calves born during the winter months.

Exposure to infection

Due to its poor immune capability, a new-born calf is vulnerable to infection. The main risk factors increasing the exposure to infection and further lowering the defence mechanism within the calf in early life are:

• Poor hygiene and overcrowding in the calving facility;
• Poor hygiene and overcrowding in the calf pens;
• High relative humidity because of overcrowding;
• Low temperature of the incoming air;
• Contamination of the incoming air;
• Inadequate ventilation;
• Close proximity to adult cows;
• Mixing of different age groups; and
• Poor stockmanship/motivation of the herdsperson responsible for the calves.

Feeding

Scours caused by digestive disorders in calves are common in artificially fed calves. Irregular feeding, changes in the temperature of the milk replacer or whole milk and stressed calves are all risk factors for this type of calf diarrhoea. Incorrect positioning of buckets or artificial teats can also cause digestive disorders, leading to diarrhoea.

The milk replacers are often associated with particular digestive problems in young calves, but their use is not relevant in organic systems, other than in emergency situations.

Suckled calves are least likely to suffer from digestive disorders. Changes in the diet or pasture of the dam may result in sudden changes in the milk composition, causing diarrhoea in the calf. "Milky" cross-bred suckler cows and dairy cows used in single-suckler units can also cause diarrhoea in the calf, who easily overeats on a generous milk supply, particularly if transferred to a "milky" dam from a more restricted diet.

Calf diarrhoea and infectious agents

Whilst infectious agents are important factors in the development of calf diarrhoea, many of them (e.g. corona- and rotavirus and Cryptosporidium) are often present in healthy animals and their environment without causing overt disease. Other infectious agents (e.g. enterotoxigenic E. coli, Salmonella spp.) are usually absent but, when introduced to the environment, tend to cause an outbreak of diarrhoea. In the case of scours caused by digestive disorders, the infectious agents have no role at all.

Most cases of calf diarrhoea are likely to be mixed infections, where more than one of the pathogenic agents is present. Mixed infections with rotavirus and Cryptosporidium appear to be most common. Experimental work also suggests that infection with one agent makes the calf more vulnerable to other pathogens. Coronavirus is the third most common diarrhoea agent. Salmonella is isolated fairly often from disease outbreaks, particularly S. dublin in calf rearing units where calves are bought in from multiple.

Diagnosis

Determining the cause of a scour outbreak is important as it may indicate future lines of prevention and may show any potential zoonotic risks, as several organisms causing scour have the potential to cause severe disease in humans.

However, this can be difficult as many cases are multifactorial, therefore a thorough investigation should include a study of dry cow management and calving practice as well as calf management.

Whilst it is important to identify the infectious agents in outbreaks of calf diarrhoea on a farm basis in order to target prevention and control of this disease complex, there are some common approaches to husbandry and management that are likely to reduce the incidence of calf scours, independent of the causative factors.

These approaches can be divided into three areas:

1. Maintenance of disease resistance;
2. Reduction of exposure to infection; and
3. Good feeding practices.

Maintenance of immune status:

1.  
   • Do not separate the dam until 24 hours after calving
   • Provide adequate bedding to allow the calf to stand without difficulty
   • Ensure early feeding, assist if needed, monitor the intake as closely as possible and record it ("maximum supervision, minimum interference")
   • Keep a supply of frozen colostrum in case the dam leaks colostrum before calving. Fermented whole colostrum can also be used, preferably from dams that have been vaccinated for scour pathogens.
   • Feed the calves colostrum as long as possible, to provide passive, "in-gut" protection against viral diarrhoea
   • Encourage outdoor calving
   • In the case of a specific, identified agent and a continuous problem, immunise pregnant dams before calving as part of a targeted control plan.

Minimisation of exposure:

• Provide adequate numbers of calving pens and cleans and disinfect them between batches
• House calves of different ages in different rooms or with adequate separation
• House calves well away from the calving pens
• Avoid overcrowding in calf housing
• Keep up high hygiene standards throughout the calving period and in calf housing
• Disinfect all feeding equipment daily.
• Consider spreading the calving period over a longer period of time (maximum 15 calves per month).
• Ensure good Biosecurity practice to reduce the risk of exposure to disease agents.

Good feeding practice:

• Suckle calves either with own dam or in a multiple suckler system
• Feed fresh or fermented colostrum  to all calves for as long as possible
• Do not feed mastitis milk or milk with antibiotics to calves
• Use teat buckets or automatic feeders rather than buckets if possible
• Make sure that feeding position is correct
• Feed regularly, the more often the better, and make sure that the milk is not too cold
• Provide constant access to fresh water
• Good quality solid feeds such as good hay should be made available from the first few days of life to encourage a smooth transition to weaning at a later date.

Reduction of stress:

• Avoid overcrowding in calf pens
• Avoid wet bedding
•  Make sure that calves are well bedded during cold weather and do not suffer from draught
• Provide shelter during prolonged cold and wet conditions on pasture

Consultation with the veterinarian is recommended.

This information was taken from:

http://www.vetsweb.com/diseases/calf-scour-d222.html#medication

For more information see:

http://www.organicvet.co.uk/Cattleweb/disease/Scour/scour1.htm