Measuring fiber and its effectiveness in ruminant diets

It appears that ruminants such as cattle and sheep evolved as forage consumers. Plant cell walls, which we measure as fiber, cannot be digested by animals, but must be fermented by microorganisms. Fermentative digestion of fiber is slow and incomplete, and ruminants have developed many attributes that result in efficient digestion. They swallow large particles of forage and selectively retain them in the rumen to allow adequate time for fermentation. They regurgitate and rechew the large particles (rumination) to enhance digestion and allow passage through the digestive tract. During chewing, they produce salivary buffers that help maintain the pH in the rumen. Ideally, roughages should be an integral part of the diet of ruminants to take advantage of their unique digestive capability. However, there are nutritional, operational, and economic reasons for limiting the forage or roughage content in some ruminant rations.