Chapter 61 Diseases of the Digestive System
Sheep and goats are ruminants; that is, they have four chambers to their “stomach.” The parts are the rumen, reticulum, omasum, and abomasum. The abomasum is the portion of the tract that is most similar in function to the monogastric stomach. As an animal grazes it swallows the forage material, which goes into the rumen. After the animal is done grazing, it finds a spot and lies down in sternal recumbency. The animal then regurgitates what it has eaten and proceeds to chew it. Sheep and goats typically chew approximately 40 times; then they swallow the bolus again. They repeat the procedure, and when the particle size is small enough, the animal swallows it and the chewed food proceeds into the reticulum.
Although the ruminant digestive system is fairly adaptable and a ruminant can eat a lower quality of forage, they still need a quality diet. Fortunately, digestive system diseases in ruminants are uncommon.
Bloat is the accumulation of free gas or froth in the rumen. Bloat is less common in small ruminants than in cattle, and it occurs less frequently in goats than in sheep. Bloat can occur from ingesting diets such as high-legume diets or cereal grains that promote the formation of froth in the rumen. Some diets, again such as those high in grain, promote the formation of free gas. Sometimes an animal will have an accumulation of free gas in the rumen because of a failure to eructate.
Rumen acidosis is caused by the rapid fermentation of highly digestible carbohydrates. The problem occurs more often with finely ground grains because the bacteria can more rapidly ferment the carbohydrate. The condition is more commonly seen in animals that have been fed a primarily forage-based diet, and then have received a large amount of concentrate feed. As the carbohydrates are digested, the pH declines. The decline in pH causes the normal resident microfauna and flora of the rumen to die. Water is drawn into the rumen, and the animal becomes dehydrated and may die. The acid buildup causes damage to the rumen epithelium. This allows the leakage of bacteria into the system, and the animal may become septic.
Diarrhea involves loose to runny feces, and it is defined as the increase in the volume and frequency of defecation. Dehydration and electrolyte imbalances are the concerning sequelae to diarrhea, especially in very young kids and lambs. Animals of certain ages are more prone to specific infectious causes of diarrhea (Fig. 61-1).
Figure 61-1 Ages at which infectious agents cause diarrhea in lambs and kids.
(From Pugh DG: Sheep and goat medicine, Philadelphia, 2002, WB Saunders, by permission.)
Enterotoxigenic Escherichia coli
Enterotoxigenic E. coli causes diarrhea mainly in neonatal lambs and, to a lesser extent, in kids. This type of bacteria has two main methods by which it causes disease. The first is by attachment and colonization of the intestinal villi. As these villi are destroyed, the intestine loses its absorptive capabilities. The second method is by production of an enterotoxin, which interferes with normal gut function. E. coli causes disease in young animals younger than 10 days, with 1 to 4 days of age being the most common age of onset.