PSX-B-6 Effect of slow-release urea on gas production, fermentation characteristics, nutrient digestibility and microbial protein synthesis in an artificial rumen system

Abstract

The objective of this study was to evaluate the effects of slow-release urea (SRU) on gas production, fermentation parameters, nutrient digestibility, and microbial protein synthesis using artificial rumen system. The experiment was a completely randomized design with four treatments and four replications of each treatment. The treatments were control diet (no SRU), control diet supplemented with 0.28% (U28), 0.56% SRU (U56) or control diet that was added by 1.5% more corn grain and substituted with 0.35% SRU for 1.85% soybean meal (U35-SBM). The diets were formulated to be isoenergetic (1.71 NEL Mcal/kg), but protein concentration was lower (15.48 vs. 16.24%) and starch concentration was higher (28.2 vs. 27.1%) with U35-SBM than other three treatments. Experimental period consisted of 8 d of adaptation and 7 d of sampling. Rumen inoculum was obtained from three ruminally fistulated Angus cows fed the same diet to the substrate incubated. Gas production (L/d) was lower (P = 0.02) with U35-SBM (1.51) than control (1.79) or U28 (1.92); however, methane production was not affected by treatments (average, 47 mg/d). Dry matter digestibility was greater (P < 0.01) with U35-SBM (78.5%) than other treatments (74.6%), which had no differences in DM digestibility. Total volatile fatty acid (VFA) production did not differ among treatments (average, 53.1 mmol/d), but increasing SRU supplementation linearly (P < 0.01) decreased molar proportion of propionate from 27.0 to 25.7% and linearly (P < 0.01) increased acetate to propionate ratio from 1.69 to 1.78. The ammonia nitrogen (N) linearly (P < 0.01) increased from 7.70 to 10.25 mmol/L with increasing SRU addition. Microbial protein synthesis was greater (P = 0.03) with SRU treatments (average, 83.9 mg N/d) than control (78.9 mg N/d). The present results demonstrated the benefits to add the SRU in dairy cow diet for improving ruminal digestibility and microbial protein synthesis.