Calf scours. Two words that even the most experienced cattleman dreads to hear during the calving season. I've read articles that name calf scours as the single most important cause of early calf sickness and death. It is unlikely that any single factor brings about calf scours. Likewise there is no single "silver bullet" medication or vaccination that will stop or prevent calf scours. Prevention of calf scours or minimizing the occurrence of calf scours depends upon management. Proper management depends upon understanding the complexity of calf scours and how various factors interconnect.
In plant pathology, we talk about the disease triangle; 3 conditions that are necessary for a disease to develop and manifest symptoms. We can use the same concept to help explain how calf scours develop and the severity of calf scours. The three sides of this disease triangle are: a susceptible animal, the disease organism, and environmental conditions conducive to the disease. When all three sides of the triangle are present, calf scours is going to appear and is likely to be severe unless quick action is taken. Let's examine each of the triangle sides in a little more detail.
There are factors that will pre-dispose a calf to scours. Some of those factors include: a difficult birth, poor nutrition of the mother cow, poor health of the mother cow, and slow and/or low intake of colostrum by the calf. When a cow is in a state of poor nutrition or poor health colostrum quality and milking ability are affected. This has a negative impact on calf health. Remember that a calf is born without a functioning immune system. Immunity and resistance to disease is passed on through the colostrum of the mother. The calf must ingest colostrum shortly after birth and in sufficient quantity to gain this passive resistance.
There are a variety of infectious agents or disease organisms that can cause calf scours. They may be classified as bacteria, viruses, or protozoa. The most common bacteria associated with calf scours is E. coli (Escherichia coli). These bacteria produce toxins in the intestines that damage the cells to the extent that fluids are lost, leading to the symptoms of diarrhea. E. coli related calf scours generally appears with very young calves, developing as soon as 16 to 24 hours after birth. The most common viruses responsible for calf scours are coronavirus and rotavirus. Both of these viruses will infect cells that line the digestive tract and damage those cells so that milk can not be digested or absorbed. Again the symptom is diarrhea. Generally when these viral agents are the cause of calf scours it appears when the calves are near a week of age or older. Another causal agent is protozoa, possibly cryptosporidium or coccidia. Once again, the cells lining the digestive tract are affected, leading to decreased digestion and absorption of milk along with diarrhea. Calves infected with cryptosporidium are generally in the one to three week age range. While coccidiosis is more often seen in weaned calves it can be associated with calf scours in calves at three to four weeks of age, particularly if those calves are under some kind of stress. It should be noted that it is possible that an outbreak of calf scours could be the result of mixed infections involving a combination of infectious agents.