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.

The effect of the inclusion of Leucaena leucocephala and Tithonia diversifolia in Zebu steers receiving a diet based on improved pastures such as Brachiaria decumbens and Brachiaria hybrid cv Cayman on nitrogen (N) excretion, urinary volume and rumen microbial population was evaluated. To determine the dry matter intake and nutrient excretion, eight steers were used in a 4 × 4 Latin square design consisting of four periods and four diets. Four of them were cannulated for ruminal fluid extraction and quantification of ruminal microorganisms in three times of grazing (T0, T7 and T15). Forage intake was calculated through the external marker titanium dioxide. Diet including forages with superior protein content generated an increase in the gene copy numbers of Prevotella ruminicola and total bacteria on 15 sampling day (p < 0.001). Animals receiving diets with the dietary inclusion of Leucaena and Tithonia had daily N intakes of 228 and 113.5g N intake d−1, of which they excreted 42% and 61%, respectively. Inclusion of both protein forages increased daily urinary volume (9% and 7% d−1), with respect to the pasture-based diet. This study revealed that the inclusion of 18% Leucaena in a pasture-based diet improves the dry matter intake and N retention in Zebu steers under tropical conditions.

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.

Pasture conditions influence the nutrients use efficiency and nitrogen (N) losses from deposited excreta. Part of the N is lost as nitrous oxide (N2O), a potent greenhouse gas. The objective of this study was to characterize apparent N recovery in milk of dual-purpose cattle and to quantify N2O emissions from the urine they deposit following grazing on Megathyrsus maximus cv. Mombasa. The N content in the grass and the milk produced by the cattle and the milk urea N (MUN) content were quantified in two contrasting regions of Colombia (Casanare and Atlántico). Dry matter intake (DMI) by the cattle was estimated using the Cornell Net Carbohydrate and Protein System. We used a closed static chamber technique to measure N2O emissions from soils in areas with and without urine patches (21 days in Atlántico and 35 Days in Casanare). Estimated DMI values were 11.5 and 11.6 kg DM day−1, milk production was 6.5 and 5.9 L day−1, apparent N recovery in milk was 24 and 23%, and the MUN content was 4.4 and 17.2 mg N dl−1 in Casanare and Atlántico, respectively. N applied to soil in the form of urine corresponded at rates of 20 and 64 g N m−2 and net cumulative N2O emissions were 350 and 20 mg N2O-N m−2 in Casanare and Atlántico, respectively. Despite low digestibility of offered diet, N recovery in milk was above the values reported at dairy cattle in tropical conditions. High urine-N inputs at Atlántico site did not result in high N2O emissions suggesting that the default Tier 1 emission factor (EF) which is based on N inputs would have overestimated urine-based N2O emissions in Atlántico. Comparing previous studies conducted in Colombia, we observed inter-regional differences by urine-based N2O emissions. This observation suggests that to increase certainty in estimating urine-based N2O emissions, Colombia needs to move toward more region-specific Tier 2 EF and reduce its dependence on the default IPCC Tier 1 EF. In addition, the adoption of Tier 2 EF in the cattle sector will facilitate accounting for the effect of animal diets on N2O inventories.