Animal energetics in extensive grazing systems: Rationality and results of research models to improve energy efficiency of beef cow-calf grazing Campos systems

摘要

Extensive grazing systems are subjected to constant variation in energy supply and International meat prices. In this context, animal energetics need to increase energy efficiency by strengthening the metabolic pathways toward productive/reproductive functions, with low-cost but high-impact management tools. In beef cow-calf grazing systems, grazing management, cow genotype and suckling restriction and flushing at the beginning of the mating period altered energetic efficiency as they modified nutrient partitioning from maintenance and milk production toward resumption of the estrous cycle and pregnancy. We presented a review with three research sub-models of research to improve, with low-cost management tools, beef cow productivity in grazing systems while attempting to alleviate weather variability. The first sub-model identified the optimum cow BCS at calving to achieve high pregnancy rate and its interaction with suckling restriction to improve weaning rate. Optimal cow BCS at calving can be achieved by herbage height manipulation throughout the beef cow-calf cycle. The second research sub-model focused on improve reproductive performance of primiparous beef cows that calved in suboptimal BCS (5). Suckling restriction for 12 d before a short-term supplementation (flushing) with rice bran for 22 d, increased probability of early pregnancy by 40%. Pregnancy rate was also modulated by cow BCS at calving, and was related to increased plasma insulin and IGF-I concentrations. The third sub-model incorporated herbage allowance and cow genotype through the entire beef cow production cycle and their interaction with suckling restriction and flushing. Collectively this approach was used to understand the relationships between herbage and animal productivity, stocking rate and individual and per ha production. High herbage allowance increased herbage productivity, cow herbage intake, and conversion efficiency of energy intake into calf product. Cow genotype increased herbage intake and conversion efficiency of energy intake into calf product due to greater calf BW and pregnancy rate. All together, the strategic and tactical tools used in these research models manipulated animal bioenergetics by increasing cow energy intake, changing nutrient partitioning and increasing productivity-per animal and per ha-and production efficiency of cow-calf systems in Campos grasslands.