Rumen degradation and intestinal digestibility of rumen protected amino acids: comparison between in situ and in vitro data

Lysine and methionine were protected in different ways. Lysine was either coated with long chain fatty acids, triglycerides and calcium soaps fatty acids (Lys-A); long chain fatty acids and triglycerides (Lys-B); with C16 and C18 calcium soaps (Lys-C); with hydrogenated fatty acids (C12–C18) (Lys-D). Methionine was coated with ethylcellulose (Met-A); with pH-sensitive polymer (Met-B); with C16 and C18 calcium soaps (Met-C); with hydrogenated fatty acids (C12–C18) (Met-D). The amino acids were incubated for 4, 8, 24 and 48 h in the rumen of three Holstein Friesian cows fed a base diet with grass hay (0.666), corn silage (0.162) and concentrate (0.172) (on dry matter basis). Intestinal digestibility (ID) was measured as amino acid disappearance from mobile bags. The lowest rumen nitrogen release was observed for the methionine supplement coated with the pH-sensitive polymer (Met-B). Among the fat coated products, lower nitrogen release was observed when using lysine coated with long chain fatty acids and triglycerides (Lys-B), whereas no differences were observed when using calcium soap fatty acids as coating matrices. The coating matrices affected the intestinal nitrogen release, with lower values observed when coating with ethyl-cellulose matrix. Some equations for the prediction of rumen degradability and intestinal digestibility on the basis of N solubility in buffers were developed. Nitrogen release in acetate buffer (Ab) is better correlated to rumen degradability than solubility in borate-phosphate (BPb) buffer. Concerning intestinal digestibility, the solubility in citrate buffer followed by an incubation with pancreatine give better results than the solubility in citrate buffer only.