An animal’s feed intake, and how well that feed is digested, determine the feed’s production performance. The in vitro gas production technique is a relatively simple method for evaluating feeds, as large numbers of samples can be incubated and analyzed at the same time. This method has been applied successfully at UC Davis for a variety of purposes in feed evaluation, including calculating organic matter digestibility, the metabolizable energy of feeds and kinetics of their fermentation; determining how feed value is affected by added fat, anti-nutritive factors and rumen modifiers; quantifying the energy value of feed mixtures (rations); monitoring microbial change in the rumen; synchronizing nutrient digestion; and selecting forage nutrient targets for agricultural biotechnology. More than half of the nutrients consumed by ruminant animals leave the animal unutilized and undigested, and are excreted in feces, urine and gases. The in vitro gas production method can be used to examine animal waste components that impact the environment and develop appropriate mitigations.
Near-infrared spectroscopy (NIRS) of fecal samples has been used to predict the crude protein and digestible organic matter of forages consumed by grazing animals. However, for NIRS predictions to be accurate, the equation used must be based on samples from the target population. The Texas A&M Grazinglands Animal Nutrition Laboratory has developed a NIRS program based on forages in Texas, the Midwest and Canada's lower prairie provinces. California producers have been using these equations even though they had never been evaluated for California conditions. We conducted beef-cattle digestibility trials on two California rangeland summer forages to produce forage-fecal pairs for testing the existing NIRS ones and developing new equations as necessary. The predictions from the original equations were significantly different from the true values determined in the digestibility trials. The addition of data from this research has improved the predictive capability for both crude protein and digestible organic matter in California.