PSVI-8 Effects of feeding ensiled or dried grape pomace on measures of nitrogen utilization in backgrounding cattle

Abstract

Abstract Because of its content of polyphenolic compounds, feeding grape pomace (GP) could alter nitrogen (N) utilization in cattle in a manner that limits urinary N excretion and, thus, reactive N emissions. However, the preservation method used for GP, whose shelf-life is limited when fresh, could potentially cause changes in the bioactivity of the polyphenolic compounds. This study evaluated the effects of feeding either ensiled or sun-dried GP on ruminal ammonia-N (NH3-N) and plasma urea-N (PUN) concentrations, and route of N excretion in backgrounding cattle. Six ruminally-cannulated beef heifers were used in a replicated 3 × 3 Latin square design with 21-d periods. Dietary treatments were (DM basis): 1) a typical backgrounding diet (CON), 2) CON + 15% ensiled GP, and 3) CON + 15% sun-dried GP. Grape pomace partially replaced triticale silage in the diet. Ruminal fluid (d 19 at 3 h post-feeding), blood (d 21 at 3 h post-feeding), and fecal grab and spot urine samples (d 19 at 0900, 1500, and 2100; d 20 at 0300, 1200, and 1800 h; d 21 at 0000 and 0600 h) were collected and analyzed for metabolites. Data was analyzed using PROC MIXED in SAS. There was no diet effect (P ≥ 0.48) on N intake, and ruminal NH3-N and PUN concentrations. Urine N (g/d and % of N intake) and urea-N (g/d) output were lower (P < 0.01) for heifers fed GP-containing diets than the CON diet. However, fecal N excretion (g/d and % of N intake) was greater (P = 0.01) for heifers fed GP-containing diets than the CON diet. In summary, although there was no diet effect ruminal NH3-N and PUN concentrations, feeding GP irrespective of preservation method, was effective in changing the route of N excretion from urine to feces, which is beneficial from an environmental standpoint.