Mitigação das emissões de metano entérico com pastagens consorciadas: estratégia para promover a sustentabilidade na pecuária

Abstract

Enteric methane (CH4), produced by ruminants during digestion, is one of the main greenhouse gases emitted by livestock farming. The use of legumes in pastures is a sustainable alternative, replacing nitrogen fertilization, improving animal performance, and reducing CH4 emissions. This study evaluated enteric methane emission, performance, and metabolism of Nelore heifers in mixed pastures of Marandu grass (Urochloa brizantha; BB) with desmodium (Desmodium heterocarpa; DO), compared to BB monoculture, with or without nitrogen fertilization, under rotational stocking and variable stocking rate. The hypothesis was that the inclusion of DO would reduce enteric CH4 emissions without affecting intake and animal performance. The experiment was conducted at the Experimental Station of the Extreme South of Bahia (CEPLAC – ESSUL), in Itabela-BA. Three types of pastures were established in randomized blocks with three replications: 1) BB+DO consortium; 2) BB monoculture + N with nitrogen fertilization (150 kg/ha/year); and 3) BB monoculture without fertilization. Management was through rotational stocking, with seven days of grazing and 28 of rest. Thirty-six heifers were used, divided into two groups. The stocking rate was adjusted based on 1% of body weight, using the ―put and take‖ method to adjust the stocking. Forage mass in the pre- and post-grazing phases was similar among treatments (averages of 3351 kg/ha and 2603 kg/ha, respectively). In BB+DO, the legume proportion was 25.2% before and 26.4% after grazing. The average weight of the heifers (233 kg), average daily gain (0.460 kg/day), stocking rate (1.85 AU/ha), and gain per area (98.5 kg/ha/season) showed no significant differences among treatments. The diet of heifers in the BB+DO treatment showed a 5% increase in crude protein, 58% in condensed tannins, 0.54% in organic matter, and 19% in indigestible neutral detergent fiber compared to monocultures, without changes in dry matter intake (1.88% of body weight) or dry matter digestibility (average of 54%). Nitrogen use efficiency was higher in BB+DO, with lower urinary nitrogen excretion (P=0.003) and higher microbial protein synthesis (168.2 g Pmic/kg of DOM; P=0.036). CH4 emissions per animal, per body weight, metabolic weight, average daily gain, dry matter intake, and per area were significantly lower in BB+DO heifers, with a 25% reduction compared to the other pastures, without compromising performance. It is concluded that the use of legumes such as DO is an effective strategy to mitigate enteric methane emissions, promoting sustainability without harming animal productivity.