Intake, digestibility and rumen fermentation in Nellore bulls grazing degraded or recovered pastures of Urochloa ssp. or the grass intercropped with pigeon pea

With global population growth, livestock production must be intensified with reduced environmental impact. The benefits of legume-grass intercropping are well-documented; however, no studies have evaluated ruminal fermentation and digestive kinetics. Pigeon pea, a legume intercropped with tropical grasses, can improve the nutritional value of forage, increasing digestive efficiency and mitigating methane emissions, while also reducing the need for nitrogen fertilization. Over two years, nine rumen-cannulated Nellore bulls were allocated to nine experimental paddocks (1.25 ha each; total area of 11.25 ha) in a randomized complete block design, with year as the blocking factor. Treatments followed a 3 × 2 factorial arrangement, consisting of three forage systems and two seasons (dry and rainy), with three paddock replicates per treatment: DEG, a degraded pasture; REC, recovered pasture fertilized with 200 kg of N; and MIX, mixture of legume-grass pasture. External and internal markers were used to determine dry matter intake (DMI). Grass and legume intake proportions were estimated using C3 and C4 carbon isotopes. The concentration and production of short-chain fatty acids, methane , and ammonia compounds were calculated using the ex-situ fermentation technique . Animals in DEG pasture presented a higher DMI of the supplement and higher relative energy loss as methane production, while a higher level of DM digestibility was observed in the MIX pasture. Higher ruminal concentrations of NH 3 -N were obtained for animals in the REC pasture. The lowest ruminal DM and NDF degradation rates were observed in the MIX pasture.