Digestion of Barley-Based High-Grain Diets supplemented with Rumen Degradable and Undegradable Protein in Steers-Digestion Trial

Benjamin Pamp, Marc Bauer, Greg Lardy, Sergio Soto-Navarro

NDSU Department of Animal and Range Sciences

Fifteen Holstein steers (398.2 ± 7.3 kg initial BW) were allotted by weight to one of four dietary treatments in a completely randomized design. Objectives of this trial were to determine effects of rumen degradable (RDP) and undegradable protein (RUP) on site and extent of digestion, microbial efficiency, and ruminal fermentation. Dietary treatments were arranged in a 2 x 2 factorial. Factors were RDP (+/-) and RUP (+/-). RDP source was urea and RUP was a combination of hydrolyzed feather meal and blood meal (80:20 on N basis). The basal diet was formulated to contain (DM basis) 83 percent barley, 5 percent alfalfa hay, 5 percent corn silage, 5 percent de-sugared molasses, 27.5 mg/kg monensin, and 11.0 mg/kg tylosin. The control diet (without added RDP and RUP) was formulated to contain a minimum of 12.5 percent CP, 0.7 percent calcium, and 0.3 percent phosphorus. Diets were formulated such that +RDP added 1% CP from urea and +RUP added 1 percent CP from the feather meal/blood meal combination. Steers were adapted to the experimental diets for 29 days before collection. Average DMI during trial period was 11.5 kg/d. Apparent ruminal OM digestibility decreased (P = 0.05) with RUP (41.4 vs. 35.1 ±2.2%). Digestibility of OM in the small intestine tended (P = 0.09) to increase with the inclusion of RUP (2.8 vs. 9.8 ± 2.3%). Intake and ruminal digestibility of NDF decreased (P = 0.01) with the dietary addition of RUP (2.98 vs. 2.64 ± 1.20 kg/d and 17.1 vs. 0.2 ± 5.8%, respectively). The inclusion of RDP increased duodenal NDF flow (P = 0.08) (2.45 vs. 2.87 ±2.06 kg/d) and decreased NDF ruminal digestion (P = 0.06) (17.1 vs. 4.5 ± 5.8%). The addition of RUP alone in the diet increased CP intake over control and RDP diets (P = 0.02; 1.62 vs. 1.79 ±0.07 kg/d). Total tract OM, CP, ADF, and NDF digestibilities were unaffected by RDP and RUP supplementation. These results suggest protein supplementation decreased ruminal fiber digestion and did not improve digestion of other feed fractions.

Note: This study is part of a collaborative research project that includes Animal and Range Sciences Department and the Carrington Research Extension Center

Key Words: Barley, Digestion, Ruminal Fermentation