THE RELATIVE MERITS OF FOREGUT AND HINDGUT FERMENTATION

Mammalian herbivores cannot break down cellulose except by fermentatio n, and may have fermentation chambers at either end of the gut: rumina nts have their principal fermentation chamber in the stomach but horse s ferment only in the hindgut. A mathematical model (Alexander, 1991) predicted that foregut fermenters should do better than hindgut fermen ters on poor foods, and the reverse on richer, less fibrous foods. Fur ther, the optimum gut for poor foods would have the hindgut fermentati on chamber only a little smaller than the foregut chamber. However, it has been claimed that horses do better than ruminants on poor food, a nd the hindgut of ruminants is much smaller than the rumen. In this pa per, the basic model is modified in ways designed to make it more real istic, and the effects are investigated. None of the modifications alt ers the conclusion that the optimum gut for poor food has a large fore gut fermentation chamber. However, the optimum proportions of fore-to hindgut, for pool diets, become more like those of real ruminants when account is taken of the diminishing volume of the food passing throug h the gut, and of incomplete mixing in the rumen.