Effects of high concentrations of crude glycerin on feed intake and ruminal parameters of sheep

Abstract Text: Eight ruminally-cannulated crossbred (Santa Ines × Dorper) male sheep (64.5 ± 8.5 kg) were used to evaluate the effects of high concentrations of crude glycerin on dry matter intake, and ruminal parameters. Animals were assigned to a replicated 4 × 4 Latin square design and, in pairs, were fed one of the four experimental diets. Isonitrogenous (18.4% CP) and isoenergetic (2.7 Mcal ME/kg DM) diets were composed of corn silage, soybean hulls, soybean meal, mineral premix, and crude glycerin replacing 0 (G0), 10 (G10), 20 (G20), or 30% (G30) corn cracked grain (DM basis), in a roughage:concentrate ratio of 40:60. Crude glycerin totally replaced corn grain in G30, and contained 83% glycerol, 95% DM, 6% salt, and less than 0.01% methanol. Each experimental period lasted 21 d (14 d adaptation and 7 d data collection). Animals were fed twice daily (0700 and 1900 h), and feed delivered and refused were weighed every morning to assess DMI. Ruminal pH, ammonia nitrogen (NH₃-N), and short-chain fatty acids (SCFA; acetate [C2], propionate [C3], butyrate, isobutyrate, valerate and isovalerate) were evaluated at 0, 2, 4, 8, 10, and 12 h after feeding. No interaction time of observation × treatments was observed. The DM intake tended to show a quadratic effect (P = 0.09), with greater values observed for G10 and G20 (1375 and 1336 g/d, respectively). Ruminal pH tended to linearly increase (P = 0.07), with values from 6.0 (G0) to 6.2 (G30). A tendency for a quadratic effect of ruminal concentrations of NH₃-N (P = 0.06) was observed, with lesser values for treatments with intermediate levels of crude glycerin (9.6 and 10.2 mg/dL, respectively for G10 and G20). Crude glycerin inclusion linearly decreased total SCFA (P < 0.0001), acetic acid (P < 0.0001), butyric acid (P = 0.0004), isobutyric acid (P = 0.0007), isovaleric acid (P = 0.003), and C2:C3 ratio (P < 0.0001). The production of propionic and valeric acids were not influenced by treatments (average = 8.7 and 0.5 mg/dL), however the proportion of propionate linearly increased from 21 to 34% of total SCFA produced. The inclusion of up to 30% crude glycerin in diets for crossbred sheep promotes quadratic effect on DM intake and ruminal concentrations of NH₃-N, changes SCFA profiles and increases ruminal pH. 

Keywords: glycerol, rumen, sheep