362 The Influence of Supplemental Protein Level on the Intake, Digestion, and Metabolism of Beef Cattle Consuming Low-Quality, High-Fiber Roughages

Abstract

Abstract Two studies were conducted to evaluate the influence of graded levels of supplemental protein on the intake, digestion, ruminal fermentation, and metabolism of beef cows consuming low-quality forage base diets (6% CP and 74% NDF). For both studies, 15 ruminally cannulated cows (4/5 yrs age, 803 and 757 kg = avg BW for study 1 and 2, respectively) were stratified by BW and, within stratum, randomly assigned to three supplemental treatment groups (n = 5). In study 1, cows were assigned to the following treatments: 1) control, no supplement; 2) 0.25 % BW of a 20% CP supplement; and 3) 0.25 % BW of a 40% supplement. Both supplements were composed of soybean meal and ground corn with the composition adjusted to hit the target CP level. In study 2, cows were assigned to the following alfalfa pellet supplement treatments: 1) control, no supplement; 2) 0.20 % BW of alfalfa pellets, and 3) 0.40 % BW of alfalfa pellets. In study 1, forage intake, DM fill, liquid fill and total tract digestibility were not influenced by supplemental treatment (P ≥ 0.49). However, total DM intake increased linearly (P = 0.02) with increasing supplemental protein, with the 40% CP supplemented cows consuming 39% more DM than control cows. No treatment differences (P ≥ 0.97) were observed for heart rate or surface temperature just before feeding (hour 0) nor 5 hours post-feeding averaging 46.0 bpm, 15.3°C, and 35.2°C, respectively. In study 2, both forage intake and total intake increased linearly (P ≤ 0.02) with increasing amounts of supplemental alfalfa. Cattle supplemented alfalfa pellets at 0.4% of BW had 33 and 71% greater forage and total DM intake compared with non-supplemented control cows, respectively. In contrast, there were no treatment effects (P ≥ 0.11) on DM fill and total tract digestibility averaging 15.73 kg and 44.99%, respectively. In contrast, liquid fill tended to increase (P = 0.08) linearly with increasing levels of supplemental alfalfa. Heart rate nor surface temperature prior to feeding and 5-hours post feeding were influenced (P ≥ 0.83) by the addition of supplemental alfalfa averaging 51.91 bpm, 15.05°C and 31.75°C, respectively. In summary, overall total DM intake was enhanced with the addition of supplemental protein, however, only modest effects were observed in ruminal fill and total tract digestion. Additionally, heart rate and surface body temperatures were not influenced by supplemental treatments under the conditions of these studies.