High concentrations of crude glycerin change ruminal in vitro greenhouse gas emissions in feedlot sheep

The objective of this study was to evaluate the effects of high concentrations of crude glycerin (CG) on in vitro greenhouse gas emissions in feedlot sheep. Eight crossbred (Santa Ines x Dorper) ruminally cannulated male sheep (64.5 ± 8.5 kg BW) were distributed in a replicated 4 x 4 Latin square design. Treatments consisted of isonitrogenous (18.4% CP) and isocaloric (2.7 Kcal ME/kg) diets containing 0, 10, 20, or 30% CG, on diets' dry matter basis. In the diet with 30% CG, corn grain was totally replaced. The experimental diets contained 30% corn silage and 70% concentrate (corn grain [except the diet with 30% CG], soybean hulls, soybean meal, urea, minerals, and crude glycerin [except the control treatment]). The animals were housed in semi-covered individual pens and fed ad libitum twice daily. After 21-d adaptation period, rumen content was sampled to serve as inoculum for in vitro incubations. Approximately 200 mg (DM basis) of each diet and buffered rumen fluid (20 mL McDougall's buffer and 10 mL rumen fluid) were placed into 60-mL penicillin glass bottles, purged with helium gas and sealed. The gas production (mL/g DM and mL/g DM disappeared), terminal pH, and DM disappearance were evaluated after 24-h incubation at 39°C. DM disappearance was obtained filtering and drying incubation residues. Gas production was estimated using a digital pressure meter and a transducer, while CH4 and CO2concentrations were obtained using gas chromatography. Data were analyzed using MIXED procedure, with fixed effects of diet and period, and random effects of sheep (diet). Orthogonal contrasts were used to determine the linear and quadratic effects of CG. Total gas production was linearly increased with inclusion of CG to the diets (P = 0.04), while CO2 production tended to decrease (P = 0.10), decreasing proportion of CH4 in total gas. DM disappearance was not affected by treatments (average = 46.7%), and when this parameter was taken into account in the gas production calculation, the same effect was observed for total gas production (P = 0.04), and CO2 production linearly decreased (P = 0.03). The increasing inclusion of CG in the diets linearly increased terminal pH (P = 0.02). In conclusion, high concentrations of crude glycerin have no effect on diets' DM disappearance, but increase in vitro total gas production, decreasing proportion of CH4 and increasing terminal pH.