38. Impacts of Forage Type and Energy Supplementation on Dry Matter Digestibility and Ruminal Nitrate Release.

Abstract The objectives of this study were to determine how forage type (haylage vs. dried hay) with or without energy supplementation influences rumen nitrate release, nutrient digestion, and rumen dynamics. Sixteen ruminal fistulated cows (avg age = 7.5 yrs; BW = 811.8±64.3 kg) were stratified by weight and, within stratum, randomly allotted to the following 2 x 2 factorial treatments: 1) dried hay with no supplement (H), 2) dried hay with cracked corn supplement (HC), 3) haylage with no supplement (HG), and 4) haylage with cracked corn supplement (HGC). Cracked corn was supplemented at 0.3% of body weight daily. Cows were individually housed and had ad libitum access to feed and water. Cows were adapted to their respective diets for a period of 14 days. Total collections of feed, orts, and feces occurred on days 15-20 with rumen dynamics measured on days 21-22. All statistical analysis was completed in R. There was no forage type by supplementation interaction or supplementation effect on digestion and intake characteristics (P ≥ 0.10). A tendency for greater dry matter digestibility was observed in cattle fed haylage compared to hay (P = 0.06). Total rumen dry matter volume, rumen dry matter volume per kg body weight, liquid volume, and rumen NDF were not influenced by forage type (P ≥ 0.13), although rumen fluid expressed as per unit of body weight tended to be greater in cattle fed dried hay compared with those fed haylage (P = 0.09). As expected, rumen pH was affected by hour post-feeding (P < 0.001). Cows fed haylage had reduced pH compared to cows fed dried hay (P = 0.03). Neither the three-way interaction of supplementation, forage type, and hour nor the two-way interactions impacted rumen pH (P ≥ 0.22). Rumen ammonia concentration had a supplement × hour interaction (P = 0.04), with cows consuming supplement having reduced ammonia concentrations compared to the non-supplemented cows for the first six hours post feeding. Total VFA concentrations tended to have forage type by hour interaction (P = 0.07), with cows fed haylage having reduced total VFAs at hour 9 post feeding compared to cows dried hay. Acetic and butyric concentrations had a forage type by hour interaction (P ≤ 0.03), with cows fed haylage having reduced acetic concentrations and increased butyric concentrations 12-hours post-feeding. The acetate:propionate ratio showed a supplement × forage type × hour interaction (P = 0.03). In general, all supplemented cows had higher acetate:propionate ratio than non-supplemented cows regardless of forage type (P ≤ 0.03). Overall, forage conservation methods and energy supplementation altered rumen fermentation dynamics and nitrogen metabolism, although effects on overall digestion were limited under the conditions of this study.