The microbial fermentation that takes place in the rumen is the process by which some nutrients, such as volatile fatty acids and microbial protein, are made available to ruminant animals. During the enteric fermentation process, other products are also generated, such as hydrogen (H2) and carbon dioxide (CO2), which, by action of methanogenic bacteria, form methane (CH4). CH4 production represents a loss that varies in the range of 5-10 % of ingested energy, since this gas is not metabolized by the animal. Most of it is eliminated to the air via the eructation process. In addition to this loss, another issue related to CH4 production and emission by ruminants is its interference in the environment. As a member of the group called greenhouse gases (GHG), this gas has a global warming potential 25 fold higher than CO2. Based on these factors, it is important for the livestock industry to reduce methanogenesis during enteric fermentation, thus increasing the efficiency and decreasing the environmental impact of the activity. The diet consumed by the animal constitutes the main determining factor for CH4 production level in the digestive processes of ruminants. Tannins are substances which have been studied due to their CH4 emission mitigating potential. These are polyphenolic compounds from plant secondary metabolism. When ingested at low levels, tannins are able to generate a number of positive effects for animal metabolism, such as fermentation modulation, increasing the efficiency of microbial protein synthesis; higher supply of essential amino acids to the small intestine, leading to a better animal performance; as well as an inhibitory effect on CH4 production. In the present project the objective is to evaluate the supplementation of the legume forage Macrotyloma axillare, which presents total tannin level of 19 g/kg on a dry matter basis, as a nutritional management strategy aimed at mitigating CH4 emission from sheep, as well as evaluate production parameters related to the consumption of this legume by animals. Using in vitro techniques, gas production and organic matter digestibility of M. axillare will be evaluated. An in vivo experiment will be used to evaluate, for 90 days, the production performance and CH4 emission by 24 five months old Santa Inês lambs. 12 animals will be kept on a pasture of Panicum maximum cv. Aruana (control), and the other 12 will be kept on a pasture of Panicum maximum cv. Aruana intercropped with M. axillare. CH4 emission will be evaluated using the SF6 tracer technique and there will be three collection periods, of four days each. The animals will be weighed fortnightly so that the daily weight gain can be evaluated and at the end of the trial all animals will be slaughtered to evaluate the carcasses. The CH4 emission of Santa Inês lambs will be also evaluated using a small chamber system, with the animals being fed the same diets employed in the prior experiment, to establish a correlation between the results obtained with both in vivo techniques, the SF6 tracer technique and the small chamber system, with the results generated by the in vitro evaluation. At the end of this project, it is expected that the CH4 emission mitigation potential of the M. axillare will be confirmed and that the animals being fed this legume present better production performance than the control group animals. This should lead to the achievement of a nutritional management strategy that reduces the environmental impact of sheep farming and improves its productivity.
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