Effects of supplemental protein source on ruminal fermentation, protein degradation, and amino acid absorption in steers and on growth and feed efficiency in steers and heifers.

In Exp. 1, four Holstein steers with cannulas in the rumen, abomasum and terminal ileum were used to determine the effects of 1) soybean meal (SBM), 2) heated SBM (HSBM), 3) corn gluten meal (CGM), or 4) a combination of HSBM and CGM (COMBO) as protein supplements on ruminal and total tract nutrient digestibilities and intestinal amino acid flows and absorption. In Exp. 2, 24 Holstein steers and 16 Holstein heifers were used in a 56-d growth trial to study the effects of these protein supplements on growth, feed efficiency, and apparent digestibility of DM, OM, CP, and fiber components. Increasing undegradable intake protein (UIP) in diets with HSBM, CGM, and COMBO decreased ruminal fluid ammonia N concentrations (P < .05) and ruminal DM and OM digestion (P < .05) and increased flow to the abomasum and absorption from the small intestine of CP (P < .05), total amino acids (P < .05), and total essential amino acids (P < .01). Increasing UIP increased bacterial and nonbacterial CP and amino acids flowing to the abomasum (P < .05). However, UIP supplementation did not affect DMI, ADG, or feed efficiency in steers or heifers (P < .05).