Effect of volatile fatty acids, lactic acid and ammonia on rumen pH in sheep

Abstract

Data are presented on pH, volatile fatty acid, lactic acid, and ammonia nitrogen levels in the rumen of sheep being hand-fed on a wide range of diets. It is concluded that the rumen pH rarely falls outside the range 5.0-7.5 on diets on which lactic acid never accumulates in the rumen after feeding. On such diets rumen pH is closely related to the volatile fatty acid level. Evidence is presented which indicates that the pH-volatile fatty acid relationship on different diets may be considerably modified by variations in salivary secretion and in the accumulation of ammonia nitrogen in the rumen after feeding. The contribution of ammonia nitrogen to the total buffering capacity of the rumen is discussed. Lactic acid only accumulated in the rumen on diets containing high levels of soluble carbohydrate or starch. Lactic acid levels above 20 mM were always associated with pH levels below 3.0, but although levels higher than 80 mM were often recorded, lumen pH levels never fell below 4.33. On these diets rumen pH was closely related to the level of volatile fatty acid or lactic acid or both in the rumen.