Avaliação in vitro de dietas com níveis crescentes de amendoim forrageiro em substituição ao capim braquiária

Abstract

This study aimed to determine in vitro the potential for methane (CH4) reduction by including increasing levels of forage peanut in a Marandu grass–based diet, evaluating fermentative, nutritional and microbial protein production parameters. Forage samples of Marandu grass intercropped with forage peanut were harvested in the rainy and dry seasons, dried, ground (1 mm) and combined to achieve 0, 25, 50 and 100 % forage peanut inclusion. Samples (0.5 g) were incubated in 50 mL flasks containing ruminal fluid from fistulated cattle fed a 90:10 forage-to-concentrate diet at 39 °C, in a randomized block design (4 × 2 factorial). Gas production was measured by water-column displacement at predefined intervals up to 96 h, with CH4 sampled at 24 h for gas-chromatographic analysis. After gas collection, volatile fatty acids, ammonia-N, fiber fractions (NDF, ADF, lignin), crude protein, ether extract, ash, condensed tannins and 96 h in vitro dry matter degradability were determined. Increasing forage peanut proportion linearly enhanced 24 h dry matter degradability (P < 0.001), total gas production and CH4 percentage (P < 0.001) in both seasons. Nutritional quality improved, with positive slopes for crude protein (0.105 and 0.064) and non-fiber carbohydrates (0.094 and 0.1077), while NDF declined linearly (–0.204 and –0.1716). Condensed tannins and microbial protein synthesis rose (P < 0.001) as forage peanut content increased. Higher methane yield was linked to enhanced fiber degradation favoring the acetogenic pathway over propionate formation. However, additional protein and energy substrates from forage peanut boosted microbial activity and protein synthesis, suggesting a possible reduction in CH4 intensity per unit of product. Although methane yield increased with forage peanut inclusion, the greater protein and energy availability indicate that CH4 intensity per unit of output could be lowered. These findings highlight the need for in vivo studies in production animals to confirm effects on performance and methane emissions.