Why do scouring calves get so sick?
Why Do Scouring Calves Get So Sick? – Part 1. Introduction to calf scours.
In the past 15 years there have been major advances in the understanding of the physiology of calf scours. Only in the past ten years has a consensus in the research community been achieved regarding this new information. In this series of articles, we will first review what is now understood about calf scours and then provide an explanation of the recent findings by several research groups in Canada and Europe. Finally, we will discuss what else needs to be done before these more recent research findings can be translated into everyday protocols on the farm.
There are four parts to a typical case of calf scours.
- Dehydration: This is a decrease in the total amount of water in the calf’s body. For more than forty years, calf growers have been taught that dehydration is the primary problem in calf scours. Calf growers are very familiar with the signs of dehydration, primarily eyes that are sunk back in their sockets, and stiff skin (checked with the “skin tent test”). We now understand that while we must correct dehydration (slowly), dehydration is not your worst enemy in a case of calf scours, but it is the least difficult problem to understand and correct.
- Acidosis: Acidosis is the term used to describe a condition in which there is too much acid in the calf’s body. Later, we will explain why the amount of acid in the calf’s body increases. In general, the importance of acidosis in calf scours has been recognized for over twenty years, but only recently have we come to realize that acidosis is more serious than dehydration. The change in thinking might be explained this way: instead of “electrolytes”, we need to think in terms of “alkalinizing agents”. “Electrolytes” is a term that has been used generally to describe a mixture of minerals that is mixed with water and fed to scouring calves. The objective of this treatment has generally been described in terms of “replacing lost electrolytes” and “helping the calf absorb water”. We now understand that the most important objective is to neutralize the excess acid in the calf’s body, and that repeated treatment with most “electrolyte” products intended for oral administration can result in too much of certain minerals in the calf, with potentially fatal results. Remember: in the short term, acidosis is a worse problem than dehydration, and the two conditions do not necessarily go together.
- D-Lactic Acid: In many cases, the obvious signs of a calf sick with scours – depression progressing to obvious weakness, to being unable to stand, to coma, and finally death – are due to the increase in D-lactic acid in the blood and other areas of the body. D-lactic acid is essentially a toxin that has serious bad effects on the calf’s nervous system. A very small amount of D-lactic acid is normally produced in the calf’s body as a result of normal body functions. The primary source of D-lactic acid in scouring calves has been shown to be the fermentation of undigested or partially digested milk that has moved into the large intestine. Milk and milk products should be fully digested in the small intestine, but in scours the lining of the small intestine is damaged, preventing normal digestive processes to occur, thus releasing incompletely digested milk into the large intestine.
- Toxemia: Toxemia is the term used to describe a situation in which disease-causing organisms produce chemicals that are toxic to the calf. These complex chemicals are produced by E. coli and Salmonella bacteria, and many other less frequently encountered pathogenic bacteria. For the purposes of discussing calf scours, D-lactic acid is considered separately from other toxins. Before the discovery of the important role of D-lactic acid in calf scours, many veterinarians and researchers felt that toxins were a major threat to the calf. We now understand that in most cases of calf scours toxins are not significant. Indeed, almost all of the published literature regarding D-lactic acid has reported that even very ill calves usually recover when given proper treatment for acidosis, dehydration and D-lactic acid over-load, without treatment for the disease-causing organism that initially caused the scours event. In many cases, the disease-causing organism is a virus, which is not directly treatable, and there have been some controlled studies done that suggest that giving antibiotics to scouring calves may do more harm than good, except in very specific cases (although the topic of drug treatment for scours is currently a topic of considerable debate within the research community). Medication of scouring calves will be discussed in a later installment of this series.
References: the bibliography for this series of articles is extensive. To save space, a complete bibliography will be published in the final installment of this series.