A stomach organized around microbes

Cattle are ruminants. Much of their feed is fermented by microbes before reaching the glandular stomach. The rumen, reticulum and omasum form the forestomach system; the abomasum performs glandular digestion. Fermentation also occurs farther along the digestive tract, but it is less important there than in hindgut fermenters such as horses.

This makes digestion a partnership between the animal and its microbial community. Movement mixes contents, water maintains the environment, and alkaline saliva helps buffer acidity. A disruption in this system can change both fermentation and the nutrients available to the animal. The same basic architecture belongs to small heritage cattle and large commercial cattle. Breed differences in size or production do not replace species anatomy.