Dr Sarah Chaplin, DEPI Tatura
Calf scours are a nightmare. The economic costs include treatment, vets' bills, labour and the value of any lost calves. It takes time and effort to deal with an outbreak of scours at an already busy time of year. It is stressful, frustrating and sometimes heart-breaking nursing sick calves and sometimes watching them die.
Calf scours are a symptom, not a disease, and have many possible causes:
Nutritional – overfeeding, sudden change in feed, incorrect mixing of feed or milk replacer.
Infectious – Rotavirus, Coronavirus, Cryptosporidium parvum, Salmonella species, E. coli.
Whatever the cause, scours result in dehydration, acidosis, and loss of electrolytes which can result in death. However, knowing the cause can help to plan effective preventive and treatment strategies. Preventing infectious scours is all about managing the calf's immune system and reducing exposure to infectious organisms. Unfortunately, although using best practice methods can reduce their impact, calf scours may still affect all farmers.
Calf scour vaccinations
Vaccinations are an important way to prevent calf scours and there are several available. They contain low levels or inactive strains of a disease causing organism, and work by stimulating the immune system to produce antibodies against that particular organism. This is called active immunity because the animal has produced the antibodies itself.
- When a calf is born, it has no immunity to disease and can't produce its own antibodies. Colostrum is the only source of antibodies for a newborn calf.
- At first the newborn calf can easily absorb antibodies from colostrum through its gut wall but this ability drops off rapidly.
- After 12 hours of life it can only absorb about half the antibodies that it is given. Absorption stops completely between 24-36 hours after birth.
- At about four weeks old the calf starts to produce its own antibodies but it takes time to build up its own immunity.
Colostrum contains antibodies that the cow has produced in response to disease challenges she has faced from her environment and vaccinations. She starts producing colostrum in the last three to four weeks of pregnancy and stops after calving. So vaccinating to prevent calf scours needs to take place several weeks before calving, allowing enough time for the vaccine to stimulate antibody production and for these antibodies to be included in the colostrum. You will still need a management routine that ensures your calves consume sufficient high quality colostrum from these vaccinated cows soon after birth (and that's a whole other story). Any effort to prevent scours by vaccinating cows is wasted unless the calf actually receives colostrum.
Vaccinations are a big help. They ensure colostrum contains the antibodies that you want. But vaccinations do not guarantee that your calves will not get scours. For example, if you vaccinate against Salmonella, the calf could still develop an infection from a different bacteria or virus, or develop nutritional scours. Successfully controlling scours takes a combination of management, treatment and vaccination. Your management routines need to consider the pre-calving cow, the calving pad, calf feeding and the calves' environment.
There are now vaccines available for most of the major causes of calf scours: Rotavirus, Coronavirus, E. coli and Salmonella. The other major cause of scours, Cryptosporidia, does not have a vaccine but does have prevention options you can discuss with your vet. These may not prevent all cases of scours but they will go a long way to helping.
- Vaccinations have the potential to greatly reduce the risk and incidence of scours.
- There is no such thing as a universal vaccine that will prevent all calf scours.
- Get advice from your vet to make sure you are using the right vaccines for your situation.
- Vaccinations need to be followed up with good colostrum management.
- Outbreaks of calf scours are expensive and stressful. A vaccination program can be good value for money, when considering the benefit of fewer deaths and better growth rates. On top of this, it can also provide peace of mind.
It may be too late to start vaccinating this year but if you do get an outbreak of calf scours, take some faecal samples to your vet to find out the cause. Next season you will be able to make an informed decision about whether to vaccinate and which vaccine to use.
For more information, read the 'Health Management' chapter of the Dairy Australia manual Rearing Healthy Calves.
Alternatively, you can contact Sarah Chaplin at DEPI Tatura, on (03) 5833 5273, or email email@example.com.