California Agriculture

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.