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.

The objective of this research was to determine the effect of cassava (Manihot esculenta Crantz) supplementation on enteric methane (CH₄) emissions, carbon footprint, and production parameters in dairy cows. Daily concentrate supply for Jersey and Jersey * Holstein breeds was evaluated in four treatments (T): T1: 100% commercial concentrate; T2: 70% concentrate + 30% cassava leaves; T3: 70% concentrate + 30% cassava roots; and T4: 70% concentrate + 15% cassava leaves + 15% cassava root chips. Measurements of CH₄ emissions were performed using the polytunnel technique. Average daily dry matter intake ranged from 7.8 to 8.5 kg dry matter (DM). Cassava leaves were characterized by a high crude protein (CP) content (171 g CP/kg DM), with 5 times more neutral detergent fiber (NDF) content than cassava root (587 vs. 108 g NDF/kg DM). Average enteric CH₄ emissions per animal ranged from 194 to 234 g/d (p > 0.05). The carbon footprint was reduced by replacing 30% of the concentrate with cassava leaves and/or roots. Energy-corrected milk production was 1.15 times higher in Jersey * Holstein animals than Jersey cows (47 vs. 55 kg). Therefore, supplementation with cassava leaves and/or roots is a nutritionally and environmentally sustainable strategy.

This study evaluates the effects of the inclusion of two different Leucaena species as a source of condensed tannins based on in vitro fermentation, methane production and post-ruminal protein supply in a diet based on Urochloa hybrid cv. Cayman CIAT BR02/1752 grass. Under in vitro conditions, Leucaena leucocephala CIAT 17263 and Leucaena diversifolia ILRI 15551 were incubated in two proportions (25% and 50% w/w) with Cayman grass and with/without polyethylene glycol as a tannin-binder. The results show that substrates with Leucaena diversifolia produced less gas and methane than those with Leucaena leucocephala with and without polyethylene glycol. The mass in undegraded feed + solid associated microbes fraction decreased linearly with increasing level of inclusion of both species of Leucaena, while increasing its nitrogen content. It is concluded that the condensed tannins of Leucaena diversifolia possess the superior activity and that the tannin content of both evaluated Leucaenas did not affect the diet degradation, and reductions in post-ruminal protein did not occur in the present study. Further studies are needed to differentiate the tannins present in different Leucaena species and their dietary effects.

Simulation models represent a low-cost approach to evaluating agricultural systems. In the current study, the precision and accuracy of the RUMINANT model to predict dry matter intake (DMI) and methane emissions from beef cattle fed tropical diets (characteristic of Colombia) was assessed. Feed intake (DMI) and methane emissions were measured in Brahman steers housed in polytunnels and fed six forage diets. In addition, DMI and methane emissions were predicted by the RUMINANT model. The model’s predictive capability was measured on the basis of precision: coefficients of variation (CV%) and determination (R², percentage of variance accounted for by the model), and model efficiency (ME) and accuracy: the simulated/observed ratio (S/O ratio) and slope and mean bias (MB%). In addition, combined measurements of accuracy and precision were carried out by means of mean square prediction error (MSPE) and correlation correspondence coefficient (CCC) and their components. The predictive capability of the RUMINANT model to simulate DMI resulted as valuable for mean S/O ratio (1.07), MB% (2.23%), CV% (17%), R² (0.886), ME (0.809), CCC (0.869). However, for methane emission simulations, the model substantially underestimated methane emissions (mean S/O ratio = 0.697, MB% = −30.5%), and ME and CCC were −0.431 and 0.485, respectively. In addition, a subset of data corresponding to diets with Leucaena was not observed to have a linear relationship between the observed and simulated values. It is suggested that this may be related to anti-methanogenic factors characteristic of Leucaena, which were not accounted for by the model. This study contributes to improving national inventories of greenhouse gases from the livestock of tropical countries.