In a this new article prepared by Richard Matthews, we have an excellent overview of calf scour: its causes and its treatment.
It has been said that it is a farmer’s own decision whether or not to have calf scour on their farms, or in other words that calf scour is a preventable disease. Eradication of calf scour, however, remains a pipe-dream for most UK cattle farmers and a call to treat a scoured calf is still a common one for the cattle practitioner at certain times of year. Scour accounts for around 50% of all UK calf deaths and causes significant financial losses to both beef and dairy enterprises.
Many of the pathogens that cause scour are ubiquitous on farms, and whether or not an individual calf develops scour depends on the interaction between that calf, the environment and its management.
Like other multifactorial diseases, an investigation of calf scour should start with identification of the cause or causes. Care must be taken with interpretation of samples as some of the agents that cause scour can be found even in healthy calves and their presence doesn’t necessarily mean that they are responsible for disease. Calf-side tests are now available which will give rapid answers for some of the common causes of scour, although bacteria still need to be cultured in a laboratory.
The causes of calf scour can be divided into four groups:
-Nutritional- normally self-limiting and associated with poor feeding practices.
-Bacterial-caused by Salmonella and certain strains of E.coli.
-Viral- rotavirus and coronavirus being some of the commonest pathogens isolated from calf scour.
-Protozoal- cryptosporidia and coccidia (this latter normally affecting older calves).
The age at which the calf is affected will give an idea of the likely pathogen, for instance scouring at 1-3 days old is commonly bacterial in origin, whilst calves which scour at 7-14 days are more likely to be affected by viruses and/or protozoa. Mixed infections, for example with both rotavirus and cryptosporidia, are common.
All of the agents that cause calf scour affect the flow of fluids into and out of the gut. Some, like the viruses, damage the finger-like projections that line the gut and thus reduce the surface area available for absorption. Others, like E.coli, produce toxins that stimulate the flow of fluid into the intestine. In all cases though, the end result is a calf that becomes dehydrated, acidotic (in other words the pH of its blood falls) and that suffers from loss of electrolytes, particularly sodium. The symptoms of dehydration will be familiar to anyone who has had to deal with scoured calves- sunken eyes, increased skin-tent time and lack of a suck reflex.
Oral fluid therapy is the mainstay of treating scoured calves, and has the advantage of being cheap and easy to administer on farm. The aims of fluid therapy are threefold; to provide a source of additional water and electrolytes, to improve absorption from the gut by facilitating sodium uptake, and to provide a source of energy. There are many commercial preparations available and they vary in their constituents, so it is worthwhile checking with your vet that the product you are using contains the right ingredients in the right proportions. Oral rehydration fluids should contain sufficient sodium and in addition they should provide an alkalinising agent (bicarbonate or bicarbonate precursors) to counteract acidosis.
It used to be suggested that continuing to feed scoured calves milk prolonged the diarrhoea, however research has shown that this is not the case. Feeding milk alongside electrolytes helps in the healing of the intestinal wall and avoids excessive weight loss. Scoured calves should receive at least 2x2 litres of electrolytes daily in addition to milk feeding, and badly dehydrated calves may need up to eight litres of electrolytes initially, divided into evenly spaced two litre feeds.
Severely scoured calves can no longer absorb sufficient fluid from their gut and require intravenous rehydration, by being put on a drip. This is a job for the vet, and, as a rule of thumb, if the calf can stand give oral fluids, but if it cannot then it needs intravenous fluids. Once severely dehydrated there is a point beyond which calves will not recover, so seek veterinary attention sooner rather than later if you think that you have a calf that needs putting on a drip.
If the diarrhoea is thought to be caused by bacteria, then antibiotics may be indicated for treatment, but their use in all cases of calf diarrhoea is controversial. Certainly in viral infections they will have no effect on the root cause of the problem. There is however justification in giving non-steroidal anti-inflammatory drugs, as these reduce the inflammation and pain in the GI tract associated with diarrhoea. There is a specific product (halofuginone) licensed for the prevention of cryptosporidial infection. This acts on the early stages of the parasite’s lifecycle to limit replication and hence reduce environmental contamination.
Scoured calves need supportive care, such as individual penning with a heat lamp. This also has the important benefit of reducing contamination of the environment by the infective agent. Remember that it is easy to spread the scour germs on wellington boots, so a disinfectant footdip is a good idea during a scour outbreak to prevent disease being spread from one pen to another. Scrupulous hygiene of buckets and feeding bags is vital.
Probiotics can be used to repopulate the gut of a recovered calf. The lactobaccili they contain are the inhabitants of a healthy gut and will help to re-establish normal digestion.
As with so many of the diseases that we come across on farms, prevention is the name of the game and once a calf needs oral fluids or has to be put on a drip we are starting to lose the battle. In the fight against scour two mainstays that tip the balance in favour of the calf are colostrum and hygiene. Every calf should receive an adequate amount of colostrum within 4-6 hours of birth (at least 10% of its birthweight, so 4 litres minimum for a 40 kg calf). Colostrum quality varies and it can be checked using a colostrometer.
Your vet can check that calves have absorbed adequate amounts of colostral antibodies by blood sampling some in the 2-14 day age range. Some of the infectious agents that cause scour are shed in the muck of adult animals so good hygiene is vital. Calving boxes should be kept as clean as possible and ideally cleaned out between occupants- remember the squelch test- if the bedding goes squelch when you step on it, then it is too damp. Finally, if appropriate, there are vaccines that can be given to cows precalving to stimulate antibody production in colostrum against rota and corona virus and E.coli K99.
It is unlikely that we will ever eradicate calf scour from the majority of UK farms, but, based on the theory that if you aim for the moon you might hit the chimneypots, implementation of these few guidelines will go a long way to reducing it to manageable levels.