No abstract

The aim of this study was to evaluate daily weight gain (DWG), total dry matter (DM) intake, rumen degradability of forage, and urinary excretion of mimosine metabolites by hair sheep in a silvopastoral system with high densities of Leucaena leucocephala. A completely randomized design was carried out with two treatments: treatment 1 (T1) silvopastoral system with leucaena at a density of 35,000 plants/ha and treatment 2 (T2), leucaena at a density of 55,000 plants/ha. Leucaena was associated with tropical grasses Panicum maximum and Cynodon nlemfluensis. Twenty-four male Pelibuey lambs of 23.2 ± 3.4 kg live weight (LW) were used (12 lambs per treatment). Results showed differences (P < 0.05) in DWG of T1 (106.41 ± 11.66 g(-1) sheep(-1)) with respect to that of T2 (81.33 ± 11.81 g(-1) sheep). Voluntary intake was higher in lambs from T1 (83.81 ± 04.07 g DM/kg LW(0.75)) with respect to that from T2 (71.67 ± 8.12 g DM/kg LW(0.75)). There was a difference in color of urine between sheep of T1 and T2, the latter giving positive results for the presence of metabolites derived from mimosine (3-4 dihydroxypyridine and 2-3 dihydroxy pyridone). Rumen degradability of DM of L. leucocephala was higher (P < 0.05) compared to that of P. maximum and C. nlemfluensis (72.94 ± 0.40 vs. 67.06 ± 1.50 and 63.25 ± 1.51 %, respectively). It is concluded that grazing at high densities of L. leucocephala affects daily weight gain of hair sheep, possibly due to ingestion of high amounts of mimosine which may exert an adverse effect on voluntary intake.

The effect of Leucaena leucocephala inclusion in sheep diets upon rumen function was evaluated. Nine Pelibuey sheep, 32.6 ± 5.33 kg live weight (LW), fitted with rumen cannula were used. A complete randomized block design was employed. Two experimental periods of 60 days each, with 60-day intervals between them, were used. Experimental treatments were as follows (n = 6): T1 (control), 100 % Pennisetum purpureum grass; T2, 20 % L. leucocephala + 80 % P. purpureum; T3, 40 % L. leucocephala + 60 % P. purpureum. In situ rumen neutral detergent fiber (aNDF) and crude protein (CP) degradation, dry matter intake (DMI), volatile fatty acids (VFA) production, estimated methane (CH4) yield, rumen pH, ammonia nitrogen (N-NH3), and protozoa counts were measured. The aNDF in situ rumen degradation of P. purpureum and leucaena was higher (P < 0.05) in T2 and T3. Leucaena CP degradation was higher in T2 and T3 but for P. purpureum it was only significantly higher in T3. Leucaena aNDF and CP degradation rate (c) was 50 % higher (P < 0.05) in T2 and T3, but only higher in T3 for P. purpureum. Voluntary intake and rumen (N-NH3) was higher in T2 and T3 (P = 0.0001, P = 0.005, respectively). Molar VFA proportions were similar for all treatments (P > 0.05). Protozoa counts and in vitro gas production (48 h) were lower in T2 and T3 (P < 0.05, P < 0.0001). Estimated methane yield (mol CH4/day) was higher in sheep fed leucaena (P < 0.0001). However, CH4 yield relative to animal performance (mol CH4/g LW gain) was lower in T2 and T3 (P < 0.0001). In summary, these results indicate that including L. leucocephala in sheep diets did not modify rumen fermentation pattern (same VFA ratios) nor reduce the amount of CH4 per unit of DMI (mol CH4/g DMI). However, leucaena inclusion does increase rumen N-NH3, aNDF and CP digestibility, and voluntary intake.

Methane produced by enteric fermentation contributes to the emission of greenhouse gases (GHG) into the atmosphere. Methane is one of the GHG resulting from anthropogenic activities with the greater global warming contribution. Ruminant production systems contribute between 18% and 33% of methane emissions. Due to this, there has been growing interest in finding feed alternatives which may help to mitigate methane production in the rumen. The presence of a vast range of secondary metabolites in tropical trees (coumarins, phenols, tannins, and saponins, among others) may be a valuable alternative to manipulate rumen fermentation and partially defaunate the rumen, and thus reduce enteric methane production. Recent reports suggest that it is possible to decrease methane emissions in sheep by up to 27% by feeding them saponins from the tea leaves of Camellia sinensis; partial defaunation (54%) of the rumen has been achieved using saponins from Sapindus saponaria. The aim of this review was to collect, analyze, and interpret scientific information on the potential of tropical trees and their secondary metabolites to mitigate methane emissions from ruminants.