Abstract #T382

# T382
Assessment of in vitro ruminal fermentation characteristics of lactation dairy diets supplemented with slow-release urea using continuous cultures.
F. Mason1, K. Neal2, S. Y. Yang2, J.-S. Eun*2, M. Spanghero1, 1Department of Agricultural and Environmental Science, University of Udine, Udine, Italy, 2Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan, UT.

The present study investigated the effects of supplementing slow-release urea (SRU; Optigen, Alltech, Nicholasville, KY) in 3 lactation dairy diets with different forage-to-concentrate ratios (F:C) on in vitro ruminal fermentation characteristics. The experiment was performed in a 3 (F:C) × 2 (without vs. with SRU supplementation) factorial design with 4 independent runs of continuous cultures (n = 4). The 3 F:C included high-forage (HF; 64:36), medium-forage (MF; 51:49), and low-forage diet (LF; 34:66) on a DM basis, and alfalfa hay and cone silage were forage sources at equal proportions. Supplementing SRU considerably reduced dietary concentrations of mixture of soybean meal and canola meal (50:50 on a DM basis) in the SRU supplemented diets. Continuous culture apparatus consisted of 700-mL working volume fermentation vessels to measure major fermentation end products. Each culture was offered a diet of 20 g DM/d in 2 equal portions at 0800 and 2000 h. Decreasing forage proportion reduced ruminal pH (P < 0.01), but supplementing SRU did not influence ruminal pH. Manipulating F:C did not affect total VFA concentration; however, under HF supplementing SRU increased total VFA concentration, while SRU supplementation in MF decreased total VFA concentration, leading to an interaction between F:C and SRU (P = 0.02). Decreasing forage proportion decreased acetate proportion, but increased propionate proportion, resulting in a tendency to decrease acetate-to-propionate ratio (P = 0.09). In contrast, SRU supplementation did not affect individual VFA proportions. Decreasing F:C decreased ammonia-N concentration, whereas supplementation of SRU tended to increase concentration of ammonia-N (P = 0.08). While methane production decreased with decreasing F:C (P < 0.01), supplementing SRU tended to increase methane production (P = 0.07) mainly due to its sizable increase in MF, leading to a tendency of F:C × SRU interaction (P = 0.06). Overall results in the current study indicate that supplementing SRU would be more beneficial in HF with enhanced ruminal fermentation evidenced by increased total VFA concentration.

Key Words: forage-to-concentrate ratio, ruminal fermentation, slow-release urea