Methane (CH 4 ) emissions from enteric fermentation in cattle are an important source of greenhouse gases, accounting for about 40% of all agricultural emissions. Diet quality plays a fundamental role in determining the magnitude of CH 4 emissions. Specifically, the inclusion of feeds with high digestibility and nutritional value have been reported to be a viable option for reducing CH 4 emissions and, simultaneously, increase animal productivity. The present study aimed to evaluate the effect of the nutritional composition and voluntary intake of diets based on tropical forages upon CH 4 emissions from zebu steers. Five treatments (diets) were evaluated: Cay1: Urochloa hybrid cv. Cayman (harvested after 65 days of regrowth: low quality); Cay2: cv. Cayman harvested after 45 days of regrowth; CayLl: cv. Cayman + Leucaena leucocephala; CayLd: cv. Cayman + Leucaena diversifolia; Hay: Dichantium aristatum hay as a comparator of common naturalized pasture. For each diet representing different levels of intensification (naturalized pasture, improved pasture, and silvopastoral systems), CH 4 emissions were measured using the polytunnel technique with four zebu steers housed in individual chambers. The CH 4 accumulated was monitored using an infrared multigas analyzer, and the voluntary forage intake of each animal was calculated. Dry matter intake (DMI, % of body weight) ranged between 0.77 and 2.94 among diets offered. Emissions of CH 4 per kg of DMI were significantly higher (P < 0.0001) in Cay1 (60.4 g), compared to other treatments. Diets that included Leucaena forage legumes had generally higher crude protein contents and higher DMI. Cay1 and Hay which had low protein content and digestibility had a higher CH 4 emission intensity (per unit live weight gain) compared to Cay2, CayLl and CayLd. Our results suggest that grass consumed after a regrowth period of 45 days results in lower CH 4 emissions intensities compared to those observed following a regrowth period of 65 days. Diets with Leucaena inclusion showed Gaviria-Uribe et al.Methane From Cattle Tropical-Forages advantages in nutrient intake that are reflected in greater live weight gains of cattle. Consequently, the intensity of the emissions generated in the legume-based systems were lower suggesting that they are a good option for achieving the emission reduction goals of sustainable tropical cattle production.

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La determinación del consumo voluntario de materia seca (CMS) por los animales, es indispensable para determinar su capacidad productiva y su estado nutricional. Existen muchas técnicas para la estimación del CMS, siendo una de ellas la técnica de n-alcanos la cual permite además estimar la selectividad de los forrajes consumidos. El presente trabajo tuvo como objetivo estimar el consumo voluntario y la excreción fecal de nutrientes por novillos cebuínos alimentados en un sistema silvopastoril intensivo (SSPi). El estudio se realizó en el Centro Experimental Cotové, propiedad de la Universidad Nacional de Colombia. Se evaluaron seis novillos castrados con un peso promedio de 381±12 kg y se utilizó la técnica de alcanos para determinar CMS. El CMS promedio de forraje fue de 9,54 kg dia-1, del cual, el 75,24 % correspondió a consumo de gramíneas y el 24,76 % a consumo de leguminosa. En promedio, el consumo de nutrientes (kg) fue de 1,33; 5,8; 4,02; 1,13; 0,058 y 0,021 para PC, FDN, FDA, Cenizas, Ca y P respectivamente. Estos consumos fueron adecuados para el tipo de animales del estudio aportando una dieta de buena calidad nutricional. La digestibilidad fue del 53 % para el tratamiento sin inclusión del suplemento y del 58 % para el tratamiento con suplemento, lo que junto con el CMS, permite afirmar que los animales satisficieron sus requerimientos de los principales nutrientes. Las cantidades excretadas (kg) fueron 4,15; 0,44; 2,56; 1,78; 0,8; 0,054 y 0,02 para MS, PC, FDN, FDA, Cenizas, Ca y P, respectivamente. La excreción fecal de N por animal al año se calculó en 29,9 kg, contribuyendo a la producción de biomasa de las gramíneas acompañantes en el SSPi.

A study of the in vitro fermentation dynamics of the forages star grass (Cynodon plectostachyus; E), Guinea grass (Megathyrsus maximus; G) and Leucaena leucocephala (L), available in intensive silvopastoral systems (ISS) was carried out. Samples of these forages were harvested in ISS set in tropical dry forest in the Valle del Cauca, Colombia. With these forages, ten mixes or different treatments were generated: E100, G100, L100, E33G66, E66G33, L33E66, L66E33, L33G66, L66G33 and L33E33G33. The shorter lag phase was observed with L100 (7.02 h) and E33G66 (7.11 h), lower (α= 0.05) than that of L33E66 (10.22 h) and G100 (9.85 h). The maximum production of gas (a) ranged between 97.34 and 253 ml/ g substrate for L100 and G100, respectively. The lowest HIP value was obtained with L100 (23.3 hours) and the gas accumulated to that point was 35.08 ml, which coincides with the lower value. The treatments that most accumulated gas were the grasses alone or their mixtures and those with the least accumulated gas included leucaena. Regarding FP, after 24 hours of incubation, the greater values occurred with L100 and mixtures that included leucaena. It is concluded that the inclusion of Leucaena was associated with decreases in the lag phase time and maximum gas production rates and with high values of FP, characteristics that may be associated with more efficient fermentation processes.