Predicting methane emissions, animal-environmental metrics and carbon footprint from Brahman (Bos indicus) breeding herd systems based on long-term research on grazing of neotropical savanna and Brachiaria decumbens pastures

Abstract

Beef cattle production constitutes the main land use in the neotropical savannas of the eastern Colombian Orinoquia. However, the effects of Brachiaria decumbens Stapf (Bd) pastures and the alternative combination of savanna and B. decumbens pastures (SaBd) to raise and breed tropical beef heifers and cows, and their impacts on methane (CH4) emissions and overall carbon (C) footprint are still unknown. This study aimed to predict CH4 emissions, animal-environmental metrics and overall C footprint across heifers' growth, cow-calf-bull and cull cows' fattening productive stages of Brahman (Bos indicus) breeding herds, lifetime-grazing on B. decumbens pastures or a sequence of native savanna and B. decumbens pastures. A dynamic model-method was used with detailed liveweight (LW) and productive lifetime-cows' data together with estimated values of above- and belowground pasture biomass and soil C stocks. This framework recognized commercial farming practices such as growing and mating female herds on Bd (Bd scenario) or rising them on savanna and grazing Bd pastures (SaBd scenario) during the herd's breeding life. The study complemented this socio-economic, cultural and productive tradition by fattening cull cows using the improved Bd pasture and illustrated the cointegrating relationship with structural-flows of LW-derived CH4 emissions. As heifers aged, accumulated CH4 emission efficiencies [t carbon dioxide (CO2) equivalent (CO2-eq) head −1] were lower in the Bd scenario than in the SaBd scenario from birth to conception (2.67 ± 0.087 vs 3.49 ± 0.087; P < .0001), while following the same trend, emissions from the first to the fourth lactation were in the range of 0.821–0.865 (P < .05) between scenarios, but similar in the two other lactations. Methane efficiency estimates from cow-calf pairs (t CO2-eq kg −1 calf born) tended to be lower in the Bd scenario than in the SaBd scenario up to the fourth lactation. In the extreme, calculated values during the fattening phase were 0.935 t CO2-eq head −1. In this context, the estimated animal greenhouse gas emissions and annual soil C accumulation values revealed not only a differentiation of the estimated C footprint at system level between animal productive stages, but also more likely natural CO2 removal from the atmosphere with all three animal phases of Bd scenarios. Hence, this study provides evidence for the experimental hypothesis that dynamic modelling based on long-term research results on improved Bd pastures would allow the estimation of the overall C footprint of Brahman breeding herds and their sustainable performance in the Colombian neotropical savanna environment.