Digestive utilization of different sources of supplemental protein by heifers grazing bermudagrass

Abstract

Supplementation of protein to calves grazing actively growing pastures has been shown to increase animal performance. The role of protein supplementation is to stimulate: 1) forage intake and digestibility, 2) microbial protein (MP) synthesis in ruminal fluid and 3) provide adequate amount of undigested intake protein (UIP), which together with MP will be absorbed in the small intestine to meet the protein requirements for ruminant tissue growth. The purpose of the research reported here was to evaluate the effect of different sources of organic nutrients and their blends on feed intake, digestibility, and digesta flow using stocker heifers grazing bermudagrass. Seven Brahman heifers (average initial BW 230 kg) were assigned to seven supplement treatments during three 15 d periods in a 3 X 7 Youden square design while grazing late season bermudagrass pasture. Supplements consisted of the following: minerals only (MIN), corn (CRN), corn gluten meal (GLU), cottonseed meal (CSM), feather meal (FEA), corn gluten/feather meal (GFE) or corn gluten/cottonseed/ feather meal (GCF) all contained Bovatec. The protein containing supplements were formulated to contain 35% CP and 2.5 Mcal ME/kg, and were individually fed at .2% BW per day. Lanthanum and chromium were dosed to serve as flow markers and to estimate fecal output. Single pulse doses of CO-EDTA (solution), ytterbium (forage), and samarium (supplement) were used to estimate turnover rate parameters. Extent of digestion was determined using INDF. Intake was calculated from the estimated fecal output and digestibility. There was a significant effect (P < .05) due to supplementation on gastrointestinal total OM and forage OM digestibility; gastric OM digestibility; OM, NDF, and INDF fecal output; total protein flow to duodenum; OM, NDF, and INDF flow to rectum; and total and forage OM intake. No differences (P > .05) were detected on fiber digestibility; nor on flow of OM, NDF, and INDF to duodenum; nor on turnover rate parameters due to treatments. The only significant differences (P < .05) found in turnover rate parameters were due to site and marker. These data implied that flow and composition of feed amino acids escaping to the duodenum have a nutritional effect in regulating forage intake.