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Cattle production systems are an important source of greenhouse gases (GHG) emitted to the atmosphere. Animal manure and managed soils are the most important sources of emissions from livestock after enteric methane. It is estimated that the N2O and CH4 produced in grasslands and manure management systems can contribute up to 25% of the emissions generated at the farm level, and therefore it is important to identify strategies to reduce the fluxes of these gases, especially in grazing systems where mitigation strategies have received less attention. This review describes the main factors that affect the emission of GHG from manure in bovine systems and the main strategies for their mitigation with emphasis on grazing production systems. The emissions of N2O and CH4 are highly variable and depend on multiple factors, which makes it difficult to use strategies that mitigate both gases simultaneously. We found that strategies such as the optimization of the diet, the implementation of silvopastoral systems and other practices with the capacity to improve soil quality and cover, and the use of nitrogen fixing plants are among the practices with more potential to reduce emissions from manure and at the same time contribute to increase carbon capture and improve food production. These strategies can be implemented to reduce the emissions of both gases and, depending on the method used and the production system, the reductions can reach up to 50% of CH4 or N2O emissions from manure according to different studies. However, many research gaps should be addressed in order to obtain such reductions at a larger scale.

T. Diversifolia can growth in acid soils including high levels of aluminium and low levels of phosphorus. 9 It is important to mention that T. Diversifolia is able to take mobilized phosphorus from the soil to the plant, which is a positive characteristic for most of tropical soils. It requires 800 to 5.000mm of water, 16 to 30°C and can growth from sea level to 2.500m altitude. 9 Usually, T. Diversifolia occurs in marginal area as of roads, around crop fields and hedges or close to farm houses. In Latin America and Caribbean (Colombia, México, Cuba, Panama, Dominican Republic and Brazil) pure stands are growing fast as farmers start to recognize the high biomass production and nutritional value of the plant. Usually, T. Diversifolia is propagated from stem cuttings of 20 to 40cm length, inserted vertically into the soil, 10 to 20cm deep. Seeds can also be used as they germinate under the canopy or even in plastic bags, and then seedlings transplanted to other areas. The main benefit of this method is that the roots will grow deeper in the soils, compared to vegetative method, and the growth is improved. However, the biomass production is influenced by soil quality, planting methods, cutting frequency, stand density and weather. 9,12,13 Although it has been used as a fodder for animal nutrition, 4,7,8,14 there are several uses reported for T. Diversifolia like insect repellent and negative effect against ants, 15 allelopathic effect against other plants, 16,17 source of nectar for bees 18 and sources of nutrients (N, P and K) for degraded soils as the biomass is quickly decomposed and consequently nutrients are easily released to the soil. 2,19 Nutritive value The studies developed by The University of Sao Joao del-Rei-Brazil (UFSJ) and CIPAV (Colombia) showed promising results for the use of T. Diversifolia as forage for ruminant nutrition. The chemical constituents of whole plant, leaves and stem obtained during the booting and pre-flowering stage when plant height reached 0.80-1.0m from the soil are good examples of important elements that could provide positive evidences of the nutritional values of T. Diversifolia. 20 The total dry matter (8.1ton/ha for booting and 5.6t/ha for pre-flowering) and fresh production (41.3ton/ha for booting and 24.7t/ha for pre-flowering) of whole plant were also included (alley crop system). The protein values during the booting (164.7g/kg DM) were higher compared to pre-flowering (149.1g/kg DM) stage. These values are as high as the values observed in some tropical legumes like, Stylosanthesguianensis (162.0g/kg DM), 21 Arachispintoi (180.0g/kg DM) 22 Gliricidia sepium (139.0g/kg DM) 22 and are higher

Tithonia diversifolia (Mexican sunflower) is a shrub used for animal feed that has outstanding agronomic and chemical characteristics. Its potential to modify the dynamics of fermentation and improve the supply of nutrients to ruminants has received considerable attention. This study was designed to determine the effect of different genotypes of T. diversifolia on ruminal fermentation and degradation of dry matter (DM), concentration of volatile fatty acids, and production of methane (CH4) when mixed with a low-quality tropical grass, Urochloa brizantha (palisade grass). In a randomised complete block design, mixtures of seven genotypes of T. diversifolia with U. brizantha cv. Marandú were evaluated by using the in vitro gas production technique. The effect of fertilisation was also evaluated for each genotype. Inclusion of T. diversifolia significantly (P < 0.05) increased the supply of nutrients and modified fermentation parameters. DM degradation of biomass after 72 h was greater in the presence of T. diversifolia than for feeds based only on U. brizantha (68.0% vs 63.4%; P < 0.01). CH4 production was lower (P < 0.05) during fermentation with some T. diversifolia genotypes (25.3 vs 27.7 mg CH4 g–1 incubated DM), and the acetic:propionic acid ratio was also lower. Fertilisation of T. diversifolia genotypes increased DM degradation, increased the content of certain nutrients (e.g. crude protein) and modified CH4 production. Therefore, inclusion of T. diversifolia in mixtures based on low-quality tropical grasses such as U. brizantha increases the supply of nutrients (crude protein, minerals, energy) and can modify the products of enteric fermentation, with some genotypes decreasing enteric CH4 emissions.

Keynote paper presented at the International Leucaena Conference, 1‒3 November 2018, Brisbane, Queensland, Australia.The demand for milk and dairy products globally is expected to grow in future decades, leading to an increase in the global dairy cattle population. Therefore it is important to identify production options that both improve efficiency and help reduce negative effects on the environment. Intensive silvopastoral systems have been proposed as a sustainable strategy in the tropics to increase the availability and quality of forage throughout the year for milk production from cattle. This paper reports the effects of silvopastoral systems that include leucaena at the farm level on milk production and on the environment in both Colombia and Mexico. Evaluation of different milk production systems has shown that the leucaena-based systems increased milk production both per cow and per hectare, increased the production of milk solids, improved the fatty acid profile in the milk and resulted in environmental benefits when compared with conventional systems.

Plenary paper presented at the International Leucaena Conference, 1‒3 November 2018, Brisbane, Queensland, Australia.Leucaena leucocephala has played a key role in the development of sustainable cattle ranching in Latin America. This species is the backbone of the so-called Intensive Silvopastoral Systems (ISPS) that combine high-density cultivation of leucaena as fodder shrubs (4,000–40,000 plants/ha) with grasses and trees. The layers of vegetation added by shrubs and trees increase the system’s capacity for transforming solar energy into biomass and enhance habitat complexity. Although part of the biomass is transformed into livestock products, a significant amount is deposited as litter on the soil and, along with the nitrogen fixed by leucaena and other trees, has positive effects on soil properties and grass production. The increased complexity of the system has measurable effects on biodiversity. ISPS with leucaena support more species of birds, ants, dung beetles and woody plants than conventional pasture monocultures, contribute to landscape-scale connectivity and provide environmental services. They also enhance animal welfare through reduced heat stress and improved availability and quality of fodder resources. ISPS contribute to climate change mitigation by improving above- and below-ground carbon sequestration and by cutting down greenhouse gas emissions per units of dry matter consumed and cattle product. Although these systems have been successfully implemented in Colombia, Mexico and other countries, their adoption is still limited in relation to the area suitable for their introduction.

Tithonia diversifolia is a shrub with excellent forage characteristics that has shown a wide genetic and phenotypic diversity. The objective of this study was to determine the biomass production and nutritional quality of seven genotypes of T. diversifolia with outstanding characteristics for ruminant nutrition, to analyze the Genotype x Environment (GxE) interaction of biomass production and to compare the performance of these genotypes with grasses offered normally in tropical conditions. For the GxE interaction the AMMI and SREG models were used, and evaluations were made in three environments. In the GxE analysis, the interaction was significant and effects of the environment on biomass productivity were observed with differences between genotypes (p <0.05). In the three environments, the chemical composition was adequate to be offered to ruminants. It is worth noting the high content of crude protein (28.89 g/100 g of dry matter - DM), the low fiber content (30.95 g of neutral detergent fiber - NDF/100 g of DM) and the high percentages of in vitrodegradation of DM for all the genotypes. It is possible to conclude that there are superior genotypes of T. diversifolia with the ability to have good productive and adaptive performance for high-altitude and low-altitude zones with low fertility soils.