1676
Ruminal fermentation of steers fed crude glycerin replacing starch- vs. fiber-based energy ingredients at low or high concentrate diets
Twelve ruminally cannulated Nellore steers (401.0 ± 41.5 kg) and 24 mo were used in a replicated truncated Latin Square arrangement of treatments with six animals in six treatments and four periods to evaluate the effect of crude glycerin (CG; 80.34% of glycerol) replacing starch- or fiber-based energy ingredients in the concentrate on ruminal pH, ammonia-N concentration and VFA’s production of the steers fed in feedlot. Experimental periods were 15 d (14 d for adaptation and 1 d to sampling). Diets were: CO - without CG and corn as ingredient of concentrate; CGC - inclusion of CG (10% of DM) replacing corn in the concentrate; and CGSH - inclusion of CG (10% of DM) replacing soybean hulls (SH) in the concentrate. All three diets were offered at a low (LC) or high concentrate (HC; 40 or 60%). Ruminal contents were obtained at 0, 2, 4, 6, 8, 10 and 12 h after 0700 h feeding. Data were analyzed as a truncated Latin Square using the MIXED procedure of SAS. The pH, ammonia-N and VFA, were analyzed as a repeated measurements. The least-squares means were generated and compared (P ≤ 0.05) using Tukey’s test. The pH was lower to animals fed HC diets than pH from animals fed LC diets (P < 0.01). No differences were detected in pH when animals were fed with CGC or CGSH. Animals fed diets CGSH had lower ammonia-N concentration than animals fed diets without CG or CGC (P < 0.01). The propionate concentrations (P < 0.01) and A:P ratio (P < 0.01) were affected by inclusion of CG in diets replacing corn or SH in the concentrate. Animals fed diets CGC or CGSH had higher propionate concentrations and lower A:P ratio in ruminal fluid (P < 0.05). There was an interaction between concentrate level and the diets for acetate (P = 0.03) and butyrate concentrations (P = 0.05). The decrease in acetate concentrations were observed in animals fed CGC or CGSH in LC than animals fed LC diets without CG. Butyrate concentrations were greater in diets CGC or CGSH, mainly in LC diets (P = 0.05). The inclusion of CG in diets did not alter the ruminal pH, but increase butyrate and reduces the A:P ratio as a result of increases of propionate concentrations.
Keywords: glycerol, propionate, ruminal pH