The sustainability of livestock production systems is vital for providing quality food, safe and accessible to the growing human population and it is essential that these systems are adaptable to the current issues of climate change and the needs of the population. Increase the use of good quality forage, avoid overgrazing and increase the rational use of legumes can be a key point in optimizing the use of grazing, reducing waste of nutrients from livestock production systems. The use of intercropped pasture is an option that fits in the most prevailing scenario of the Brazilian ruminant livestock production system and besides of providing better productivity indices it also presents potential for contributing as a methane (CH4) mitigation strategy for this sector. Estimates of consumption of fodder for animals on pasture are limited and there is need to know with accuracy the quantity and quality of the nutrients consumed by the animal in order to optimize the sustainability of livestock production. The legume Macrotyloma axillare NO 279 (macrotiloma), which is adapted to the tropical climate, has presented good performance under intercropping situation and CH4 mitigation potential in experiment with lambs. Therefore, it is necessary to precisely evaluate the CH4 emission of cattle fed on this legume. For the present study 32 Jersey heifers (presenting between 8 and 14 months old and approximately 150 kg of body weight) will be randomly distributed in 2 treatment groups, in a completely randomized design, with one group feeding on exclusive Brachiaria brizantha cv. Marandu (Hochsct ex.A. Rich) Stapf. (marandu grass) pasture (control) and the other feeding on a pasture of marandu grass intercropped with macrotiloma, with the following objectives: to measure the in vivo CH4 emission of the animals by using the sulphur hexafluoride (SF6) gas tracer technique; to determine the carbon isotopic composition of the collected CH4 samples; to evaluate fermentative parameters and perform rumen microbes quantification analyses of the animals; to estimate dry matter intake level by using the X-ray spectroscopy technique; and to determine macrotiloma tannins characteristics, by evaluating its condensed tannins structural features (mean degree of polymerization; the ratio between prodelphinidins : procyanidins; and the ratio between cis : trans flavan-3-ols) and by performing in vitro bioassays using polyethylene glycol (PEG), which indicates the biological activity of tannins. Four CH4 measurement periods (7 days each) will be carried out along the four seasons of the year: August 2017 (winter); October 2017 (spring); January 2018 (summer); and April 2018 (fall), on which besides the proposed variables, chemical, botanic and morphologic composition of the forages will be evaluated. Therefore, it will be possible to have an accurate knowledge about the anti-methanogenic potential of this legume, by thoroughly presenting details of the interaction between macrotiloma and rumen microbial system. During the first year of this project, the candidate intends to apply for a study abroad fellowship (BEPE), which will be held at the Lethbridge Research and Development Centre (Agriculture and Agri-Food Canada), in the city of Lethbridge, Alberta, Canada, under supervision of Dr. Karen Beauchemin. With the results obtained during the postdoctoral project, it is expected to consolidate the legume macrotiloma as an option for providing sustainability in the ruminant production system. The divulgation of results at the end of this project will be carried out by issuing papers in high impact scientific journals, by participating in national and international scientific events, by releasing technical notes and by conducting lectures, field days and workshops, to be organized by the 3 institutions involved in the execution of this project.
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