The objective was to evaluate milk production, N₂-fixation and N transfer, forage yield and composition (under two cutting intervals) in a silvopastoral system (SPS) with Leucaena leucocephala-Megathyrsus maximus and M. maximus-monoculture (MMM) with crossbred cows in a completely randomized design. Forage yield in the SPS was 6490 and 6907 kg DM ha⁻¹ for cutting intervals (CI) of 35 and 50 days. Forage yield for the MMM was 7284 and 10,843 kg DM ha⁻¹, and forage crude protein (CP) was 29.0% and 26.1% for L. leucocephala, harvested at 35 and 50 days, respectively. CP for the associated M. maximus was 9.9% and 7.8% for CI 35 and 50 days, respectively, and for MMM was 7.4% and 8.4%, harvested at 35 and 50 days. Milk production was 4.7 kg cow⁻¹ day⁻¹ for cows grazing MMM and 7.4 kg cow⁻¹ day⁻¹ under SPS. Nitrogen fixation in L. leucocephala (%Ndfa) was estimated to be 89% and 95%, at 35 and 50 days, with an N₂ transfer to the associated grass of 34.3% and 52.9%. SPS has the potential to fix and transfer important amounts of N₂ to the associated grass, and increase forage CP content and milk production.

In order to meet consumer needs, the livestock industry is increasingly seeking natural feed additives with the ability to improve the efficiency of nutrient utilization, alternatives to antibiotics, and mitigate methane emissions in ruminants. Chitosan (CHI) is a polysaccharide with antimicrobial capability against protozoa and Gram-positive and -negative bacteria, fungi, and yeasts while naringin (NA) is a flavonoid with antimicrobial and antioxidant properties. First, an in vitro gas production experiment was performed adding 0, 1.5, 3.0 g/kg of CHI and NA under a completely randomized design. The substrate containing forage and concentrate in a 70:30 ratio on a dry matter (DM) basis. Compounds increased the concentration of propionic acid, and a significant reduction in methane production was observed with the inclusion of CHI at 1.5 g/kg in in vitro experiments (p < 0.001). In a dry matter rumen degradability study for 96 h, there were no differences in potential and effective degradability. In the in vivo study, six crossbred heifers fitted with rumen cannulas were assigned to a 6 × 6 Latin square design according to the following treatments: control (CTL), no additive; chitosan (CHI1, 1.5 g/kg DMI); (CHI2, 3.0 g/kg DMI); naringin (NA1, 1.5 g/kg DMI); (NA2, 3.0 g/kg DMI) and a mixture of CHI and NA (1.5 + 1.5 g/kg DMI) given directly through the rumen cannula. Additives did not affect rumen fermentation (p > 0.05), DM intake and digestibility of (p > 0.05), and enteric methane emissions (p > 0.05). CHI at a concentration of 1.5 g/kg DM in in vitro experiments had a positive effect on fermentation pattern increasing propionate and reduced methane production. In contrast, in the in vivo studies, there was not a positive effect on rumen fermentation, nor in enteric methane production in crossbred heifers fed a basal ration of tropical grass.

Keynote paper presented at the International Leucaena Conference, 1‒3 November 2018, Brisbane, Queensland, Australia.The impacts of leucaena (Leucaena leucocephala) feeding systems on cattle production, environmental services and animal welfare in Mexico are discussed. A total of about 12,000 ha of leucaena have been established in the tropical regions of México, where most of the information for the current review was obtained. Incorporating leucaena in a grass pasture increases dry matter intake of grazing cattle and reduces the level of methane produced. This results in improved liveweight gains and milk yields as well as a reduction in the level of greenhouse gas released. Additional benefits are increases in soil carbon and nitrogen levels and less stress on animals as the leucaena plants provide shade and reduce environmental temperatures. While these benefits are substantial, the area developed to leucaena represents less than 0.1% of the area which could potentially be developed. Strategies to increase adoption of these grass-legume systems by farmers need to be developed to make effective use of the systems for increasing beef and milk production while reducing the undesirable environmental outcomes normally associated with ruminant production.

Background. It is agreed that there is a need to work on sustainable extensive livestock production systems. Silvopastoral systems are an alternative for efficient and sustainable grazing systems to increase the provision of ecosystems services and minimize the environmental costs associated to monoculture systems (MS), but the efficiency of intensively managed (IS) and unmanaged or native (NS) silvopastoral systems has never been assessed and compared to MS. The Framework for Assessing the Sustainability of Natural Resource Management (MESMIS) offers a tool to assess sustainability criteria in agroecosystems. Objective. To use MESMIS to compare the sustainable performance of NS, IS and MS and determine the system with the best sustainable performance in the Mexican Tropics. Methodology. One MS IS and NS per municipality (Tizimin, Merida and Tzucacab) were evaluated in the state of Yucatán, Mexico. Based on the MESMIS approach, the evaluation of the critical points of sustainability resulted in the selection of 19 indicators classified according to the attributes also defined by MESMIS (production, adaptability, stability-resilience, equity and self-management) and by sustainability dimensions (environmental, animal welfare, economic and social). After evaluation, indicator scores were obtained and integrated into attributes and dimensions through the assignation of equitable, balanced weights (W). Finally, attribute and dimension scores were aggregated in amoeba graphs to facilitate visual interpretation. Results. NS were better for the dimensions ‘Environmental’ and ‘Economic’ and the attributes ‘Stability, ‘Reliability’and ‘Resilience,’ and ‘Production’. IS were best for the dimension ‘Animal Welfare’ and attributes ‘Adaptability’ and ‘Self-reliance’. MS were better for the ‘Social’ dimension and the ‘Equity’ attribute. Implications. The fact that IS appeared to be more sustainable than MS does not leave out the idea of considering NS as a better option for some criteria such as the biodiversity conservation and the prevention of disease outbreaks, than IS. We suggest that more studies are carried on areas of potential improvement for IS as well as NS. Conclusions. This information will be useful to continue working on the parametrization of sustainability criteria of cattle extensive systems to be used for more efficient policies.

Decomposition and N release pattern from the leaves of three shrubs species were studied under field conditions. Leaves of Leucaena leucocephala (Lam.), Guazuma ulmifolia (Lam.) and Moringa oleifera (Lam.) and two mixtures, Leucaena + Moringa and Leucaena + Guazuma, in a complete randomized block design, were studied during the dry and wet seasons. Litterbags were randomly distributed in each experimental block and placed on the soil surface, and residues were recovered after 2, 4, 8, and 16 weeks. Double exponential model decay was better fitted to describe the pattern of the decay of the release of various leaf constituents. Litter dry weight loss and N release were faster from Moringa, followed by the Leucaena + Moringa mixture, while the Guazuma leaf litter decomposed much slower. In the wet period, a rapid N release was observed for Moringa (60%) and Leucaena + Moringa (43%) in the first two weeks. In contrast, Guazuma and the Leucaena + Guazuma mixture released about 46% of N in 16 weeks. In the dry period, leaves released most of their N during the first 8 to 16 weeks. Moringa and Leucaena + Moringa ranked first, having lost 81 and 75% of its initial N, respectively. The ratios of condensed tannin and polyphenols to N were significantly correlated with the N released. It was concluded that the initial mass loss from the leaf litter was high and rapid in the rainy period in comparison to the dry period. The residue disappearance pattern of Moringa, Leucaena and Leucaena + Moringa followed an asymptotic model, with more than 80% of the original residue released during the 16-week study period.