Effect of crude glycerin associated with energy sources on enteric methane emission from finishing Nellore bulls on pasture in the dry season

Abstract Text: The objective of this study was to evaluate the enteric methane emission, average daily gain (ADG) and daily carcass gain (GC) of finishing Nellore young bulls maintained on tropical pasture during the dry season and supplemented with 28% crude glycerin (CG) in the supplement (DM basis) and replacing corn or soybean hulls, with or without a source of oil. Thirty six Nellore young bulls with 510.02 ± 40.66 kg average initial BW were distributed in a completely randomized design (three animals per paddock and three paddocks per treatment) with four experimental treatments and nine replicates in a 2x2 factorial arrangement (high or low starch, with or without a source of oil). Paddock was the experimental unit, and the model effects included each treatment. The animals were raised (finishing phase) Brachiaria brizantha cv. Xaraés in the dry season (June 2013 to October 2013) with the treatments supplemented at the rate of 1000 g/100 kg BW. The supplements were: T1 - CG with high starch (corn), T2 - CG with low starch (soybean hulls), T3 - CG with high starch and a source of oil (corn and soybeans) and T4 - CG with low starch and a source of oil (soybean hulls in soybean grain). The sulfur hexafluoride SF₆ tracer method was used to measure eructated CH₄. Average daily gain (ADG) was obtained by weighing animals at the beginning and end of methane measurement period (28 days). The animals were slaughtered at day 133 of the trial with determined carcass weight. Data were analyzed using the PROC GLM procedure of SAS with significance level at P<0.05 including daily carcass gain (GC, kg day^-1) and average daily gain (ADG, kg day^-1) of the animals. Methane emission was expressed per year (kg CH₄ yr^-1), per day (g CH₄ day^-1), per kilogram of carcass produced (kg CH₄ kg CAR^-1) and per kilogram of average daily gain (kg CH₄ kg ADG^-1). Differences were not detected (P>0.05) between treatments with average values of 0.65 kg day^-1, 0.68 kg day^-1, 47.22 kg yr^-1, 129.37 g day^-1, 0.20 kg CH₄ kg CAR^-1 and 0.25 kg CH₄ kg ADG^-1, respectively. The average daily weight and enteric methane emission of Nellore bulls on pasture was not affected by supplementation of crude glycerin.

Keywords: beef cattle, glycerol, greenhouse gas