Effects of supplementation frequency on the ruminal fermentation and enteric methane production of beef cattle grazing in tropical pastures

The objective of this study was to evaluate the characteristics of ruminal fermentation and enteric methane production in beef cattle subjected to different supplementation frequencies while grazing on Brachiaria brizanthacv. Marandu pastures. Nine cattle (325±65.7 kg BW) fitted with ruminal and duodenal cannulas were used in the ruminal fermentation study, and 12 cattle (399±32.6 kg BW) were used in the enteric methane production study. The treatments included supplementation once daily, supplementation once daily except Saturdays and Sundays, or supplementation on alternate days. The supplementation was equivalent to 10 g kg−1 BW day−1 for all treatments. The design employed was completely randomized with three treatments and three replications. When all supplements were provided (day 1), no effects of supplementation frequency were observed on ruminal pH; concentration of NH3-N; concentration of acetic, propionic, or butyric acids; or total volatile fatty acids (VFA), but there were month effects. During the day on which only daily supplements were provided (day 2), significant differences were observed only on the molar concentration of acetic acid and total VFA; and month effects were noted on all variables. No significant differences were observed in ruminal fluid volume, dilution rate, N intake, bacterial N synthesis and enteric methane production among the studied supplementation frequencies. Differences were observed in the enteric methane production in the different months, with 85 g kg−1 of gross energy intake observed in September and 123 g kg−1 of gross energy intake observed in November. Lower supplementation frequency is a good option to lower labor costs with little or no consequences on ruminal fermentation characteristics and enteric methane production.本研究旨在评估在Marandu品种布氏臂形草（Brachiaria brizantha cv. Marandu）牧场放牧的肉牛，在不同补饲频率下的瘤胃发酵特性及肠道甲烷生成特征。瘤胃发酵特性试验选用9头安装有瘤胃及十二指肠瘘管的肉牛（初始体重325±65.7 kg），肠道甲烷生成试验则选用12头初始体重为399±32.6 kg的肉牛。试验设置3种补饲频率：每日补饲1次、除周末外每日补饲1次，以及隔日补饲1次。所有处理组的补饲量均为10 g·kg⁻¹体重·天⁻¹。试验采用完全随机设计，设置3个处理组，每组3次重复。试验第1天（当日完成全部补饲）时，补饲频率对瘤胃pH、氨态氮（NH₃-N）浓度、乙酸、丙酸、丁酸浓度以及总挥发性脂肪酸（total volatile fatty acids, VFA）总量均无显著影响，但存在月份效应。试验第2天（仅当日补饲）时，仅乙酸摩尔浓度及总VFA总量存在显著差异，所有观测指标均存在月份效应。不同补饲频率对瘤胃液体积、稀释率、氮摄入量、细菌氮合成量及肠道甲烷生成量均无显著影响。不同月份的肠道甲烷生成量存在显著差异：9月份每千克摄入总能对应的肠道甲烷生成量为85 g，11月份为123 g。降低补饲频率可有效降低人工成本，且对瘤胃发酵特性及肠道甲烷生成量几乎无负面影响，是一种较为理想的选择。