Ask any nonfarmer what sets cows apart from humans, and they'll probably rattle off a list that includes four legs, an udder and a tail. One underlying difference that's most basic to bovine physiology is that cows have a ruminant digestive system. Joining them among the ruminant ranks are sheep, goats, bison, deer, elk and reindeer.
Ruminant animals have a four-compartment stomach (rumen, reticulum, omasum and abomasum), each doing its part to break down fibrous materials more efficiently than animals with simpler digestive systems. Rumen microbes produce cellulase enzymes, which break down plant materials into volatile fatty acids to be absorbed by the animal to use as energy, into ammonia that is used to make microbial protein—the animal's primary protein source—and into gasses. As the food particles continue through the stomach compartments, other nutrients are absorbed.
There's no one-size-fits-all plan for feeding ruminants, even those of the same species, because nutritional needs are affected by many factors, including growth, pregnancy, lactation, fiber production, activity and environment. The microbes in the ruminant digestive system can digest and gain nutrition from even poor-quality forages, but that doesn't mean ruminants shouldn't be fed the best forage available.
Pasture is often the most economical feed for ruminants and can be high in energy and protein during the vegetation's growth stages. As grasses, browse and forbs mature, they become less digestible, so pastures should be rotated regularly for the greatest nutritional benefit. Hay and silage are substitutes when pasture is not available, and their nutrient quality varies greatly based on the fields where they were harvested, the conditions under which they were harvested and their storage environments. Concentrate feeds—grains and animal or plant byproducts, such as soybean meal or fish meal—tend to be either high in energy or high in protein and can fill in nutritional gaps where forage leaves off. Ruminant microbes have no problem digesting unprocessed grains (for example, oats that are not rolled or corn that is not crimped).
To keep a ruminant animal healthy, the microbes must be kept healthy. Fast changes in diet significantly upset the microbial population. For example, if pasture-fed sheep are suddenly changed to a grain-based diet, their digestive microbes will all be suited to forage digestion and will be unable to break down the grain. The use of antibiotics can also upset the microbial population.
Ruminants serve many purposes on the small farm, including as sources of meat, milk, draft power and fiber. Because different species prefer to graze different types of forage, having a variety of ruminant animals can benefit pasture health in a rotational-grazing management system. Cattle and sheep prefer grasses over legumes, whereas goats prefer forbs and browse; so as part of a rotation plan, a mix of these species can keep a pasture grazed down and producing well.
Click for larger view.