Intra-wet season variation in rangeland fodder quality influences feed conversion, growth and methane emissions in West African zebu cattle

Abstract

Livestock in sub-Saharan Africa is a major contributor to greenhouse gas emissions, particularly enteric methane (eCH₄), with emissions intensities and yield often elevated. In this region, wet-season rangeland fodder is the primary feed source for livestock. This study evaluated the effects of fodder growth stage and feed allowance on feed intake, digestibility, average daily gain (ADG), feed conversion ratio (FCR), and eCH₄ emissions in cattle. Over a 112-day period, including a 14-day adaptation and a 98-day data collection phase, ten Sudanese Fulani zebu bulls (52 ± 1.2 months of age, 195 ± 14.6 kg body weight) were fed green rangeland fodder. They were divided into two groups of five animals each: one received fodder at a high allowance level of 4.5 % of body weight (BW) dry matter (DM) basis (4.5ING), while the other received 2.5 % of BW (2.5ING). Voluntary intake, digestibility, and eCH₄ (GreenFeed®) were measured daily across three fodder growth stages: vegetative stage (VeS), reproductive stage (ReS), and mature stage (MaS). ADG and FCR were assessed fortnightly. DM intake decreased progressively from VeS to MaS with the highest values recorded for 4.5ING (P < 0.05). Digestibility was affected only by growth stage, decreasing from VeS to MaS (P < 0.05). Both ADG and FCR were influenced by fodder growth stage and feed level. The lowest eCH₄ yield and intensity were observed in VeS (P < 0.05). Fodder level influenced eCH₄ intensity (P < 0.05). Intra-wet season fodder growth stage significantly affected intake, digestibility, growth, and eCH₄ emissions in cattle, while feed allowance influenced performance and eCH₄ intensity. Significant interactions effects were observed between fodder growth stage and feed allowance for all parameters except digestibility. The best animal performance, along with the lowest eCH₄ yield and intensity were observed in 4.5ING animals during VeS. These findings suggest that optimizing feed availability at the beginning of the wet season is an effective feeding strategy to enhance productivity while mitigating methane emissions in extensive livestock systems.