Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/1996
Publication Date: N/A
Interpretive Summary: Because of unique chemical and physical properties of forage, nutritional conditions most limiting to performance of specific classes of ruminants are often uncertain and may differ between tropical and temperate grasses. Thus, efficiency of utilization of specific supplemental feedstuffs may vary with forage source. More nitrogen (or crude protein) of a supplement high in rumen undegradable protein (i.e., mixture of corn gluten, feather and blood meals) was lost in liver synthesis of urea with a warm vs cool season grass (i.e., bermudagrass vs ryegrass-wheat). Presumably, this was because the warm season grass provided less energy for 1) ruminal microbes to use ammonia for synthesis of microbial protein and 2) peripheral tissues to synthesize protein. Thus, rumen undegradable protein supplements may be of little value with warm season grasses unless the grass is of very high quality or a supplemental energy source is provided (e.g., cereal grain). Previously, other researchers had postulated that suspected lower ruminal degradability of protein (or high ruminal escape of protein) in warm vs cool season grass was responsible for no or little performance response when ruminants consuming warm season grass were supplemented with rumen undegradable protein. Therefore, these results are important to livestock producers and feed manufacturers in facilitating increased efficiency of supplement utilization for decreased production costs.
Technical Abstract: Wethers (37 +/- 1.5 kg body weight and 10 months old) were used to determine interactions between dietary grass source and rumen undegradable protein supplementation on splanchnic tissue net flux of nutrients. Bermudagrass (B; 73.1% NDF and 6.2% CP) or ryegrass-wheat (RW; 65.9% NDF and 8.9% CP) hay was consumed ad libitum and supplemented with 53 g/day (DM) of soybean meal (S) or S plus 70 g/day (DM) of a mixture of feedstuffs high in rumen undegradable protein (SR). The difference between digestible energy intake and splanchnic bed energy use was greater (P=0.02; 9.3 vs 6.9 MJ/day) for RW vs B. Supplementation with SR increased (P=0.04) alpha-amino nitrogen release by the PDV (6.6, 22.0, 9.8 and 20.6 mmol/h) but also increased (P=0.04) hepatic uptake (10.9, 25.6, 11.2 and 14.3 mmol/h for B-S, B-SR, RW-S and RW-SR, respectively; SE 2.29). Supplementation with SR increased (P<0.01) hepatic urea nitrogen release (26.7, 48.4, 29.0 and 41.8 mmol/h) and ammonia nitrogen uptake (17.3, 29.7, 23.3 and 26.6 mmol/h for B-S, B-SR, RW-S and RW-SR, respectively) more (interaction; P=0.09 and 0.08, respectively) with B than RW. In conclusion, greater ruminally fermentable organic matter for RW presumably minimized effects of rumen undegradable protein on ammonia taken up by the liver compared with B, and the larger difference between splanchnic bed energy consumption and digestible energy intake for RW may have been accompanied by greater amino acid use in extra-splanchnic tissue protein synthesis that limited hepatic alpha-amino nitrogen uptake.