Methane production of Nellore young bulls on pasture in the rainy season supplemented with crude glycerin associated energy sources

Abstract Text: The objective of this study was to evaluate the effect of adding 28% crude glycerin (CG) in the supplement (DM basis) , replacing corn or soybean hulls, with or without a source of oil, on enteric methane emission, average daily gain (ADG) and daily carcass gain (GC) of young bulls in the pasture. A total of 36 young Nellore bulls with an average initial BW of 333.20 ± 41.60 kg were distributed in a completely randomized design (three animals per paddock and three paddocks per treatment) with nine replicates. Treatments were arranged as a 2x2 factorial (high or low starch, with or without a source of oil). Paddock was the experimental unit, and the model effects included treatment. These animals were grazed on Brachiaria brizantha cv. Xaraés in the rainy season (January 2013 to May 2013), with the same treatments and supplemented at the rate of 500 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 associated to a source of oil (corn and soybeans) and T4 - CG with low starch associated to a source of oil (soybean hulls in soybean grain). The sulfur hexafluoride (SF₆) tracer method for measuring eructated CH₄ was used in this study (Johnson et al., 1994). To determine daily carcass gain, eight animals were slaughtered as a reference at the beginning of the experiment and after 133 days of the experiment, eight more animals were slaughtered. Data were analyzed using the SAS PROC GLM, considering the significance of P<0.05. Daily carcass gain (GC, kg.day^-1) and average daily gain (ADG, kg.day^-1) of the animals was evaluated. The methane emission were expressed in kilogram of methane emitted per year (kg CH₄.yr^-1), gram per day (g CH₄.day^-1), kilogram per kilogram of carcass produced (kg CH₄.kg CAR^-1) and kilogram per kilogram of average daily gain (kg CH₄.kg ADG^-1). Differences were not detected (P>0.05) between treatments, with average values of 0.54 kg.day^-1, 0.88 kg.day^-1, 44.03 kg.yr^-1, 120.64 g.day^-1, 0.22 kg.kg CAR^-1 and 0.16 kg CH₄.kg ADG^-1, respectively. Crude glycerin associated with high or low levels of starch, with or without a source of oil, did not alter the methane production of Nellore bulls on pasture supplemented during the rainy season.

Keywords: energy, environment, ruminant