Performance, ruminal metabolism and metagenomics of Nellore beef cattle under intensified grassland systems during rainy and dry season

Abstract

Ruminants contribute directly to increasing concentration of atmospheric CH4 through enteric fermentation, and thus nutritional techniques that allow us to manipulate the rumen may be used to mitigate the negative impact that livestock production can cause to the environment. The majority of Brazilian beef cattle production occurs in extensive grazing system, such as rotational and differed grazing without supplementation and less is known about the efficiency and the impact that this system can cause to the environment in terms of enteric methane emission. It is widely known that ruminant generates greater amount of enteric methane when fed forage as compared to concentrate diets. Therefore, it is important to assess whether utilization ammonium nitrate (NH4NO3) supplementation for beef cattle is capable of mitigating the methane daily generated from animals raised in grazing systems. Positive results in terms of improving ruminant performance, favorable change in ruminal fermentation and lower enteric methane production might give indicative of a profitable system production for tropical areas that would not only be economically appealing but also environmentally. Therefore, this experiment proposes to investigate the effects of adequate practices of grazing management (intensified deferred or rotational grazing systems with adoption of supplementation) on Nellore beef cattle performance, rumen ecosystem (metagenomics) and its effects on ruminal profile and metabolites (pH, short chain fatty acids, total ammonia nitrogen) and enteric methane production. A total of 16 Nellore steers, of approximately 280 kg in body weight and 15-16 months old, will be used as experimental animals. Of the 16 experimental animals to be used in each treatment, eight of them will be used for rumen fermentation (cannulated animals) and eight for performance evaluation. Animals will be randomly allotted to 8 paddocks. Each treatment will be allotted to a paddock in a randomized block design (blocks will be formed as a function of terrain location) during two years (total of eight replicates). Treatments will be composed by combination of two different grazing systems (stabilished with Brachiaria brizantha cv. Marandu) with supplementation of ammonium nitrate (NH4NO3) and/or urea. All variables which will include: animal performance, ruminal degradability of the diet and its components, ruminal emptying, solid disappearance rate, ruminal material for short chain fatty acids, methane, ammonia nitrogen (by mean ex situ), energy release estimative, protozoa counting and ruminal metagenomic will be collected and assessed during two periods of two years (in the rainy and dry season). Data will be statistically analyzed using the SAS 9.3. (AU)