AUTHOR=Granja-Salcedo Yury Tatiana , Fernandes Rodolfo Maciel , Araujo Rafael Canonenco de , Kishi Luciano Takeshi , Berchielli Telma Teresinha , Resende Flávio Dutra de , Berndt Alexandre , Siqueira Gustavo Rezende 

TITLE=Long-Term Encapsulated Nitrate Supplementation Modulates Rumen Microbial Diversity and Rumen Fermentation to Reduce Methane Emission in Grazing Steers

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.00614

DOI=10.3389/fmicb.2019.00614

ISSN=1664-302X

ABSTRACT=<p>This study investigated the long-term effects (13 months) of encapsulated nitrate supplementation (ENS) on enteric methane emissions, rumen fermentation parameters, ruminal bacteria, and diversity of archaea in grazing beef cattle. We used a total of thirty-two Nellore steers (initial BW of 197 ± 15.3 kg), 12 of which were fitted with rumen cannulas. For 13 months, the animals were maintained in 12 paddocks and fed a concentrate of ground corn, soybean meals, mineral supplements, and urea (URS) or encapsulated nitrate (EN) containing 70 g of EN/100 kg of BW (corresponding to 47 g NO<sub>3</sub><sup>-</sup>/100 kg BW). Encapsulated nitrate supplementation resulted in similar forage, supplement and total DMI values as URS (<italic>P</italic> &gt; 0.05), but ENS tended to increase (+48 g/d; <italic>P</italic> = 0.055) average daily weight gain. Daily reductions in methane emissions (-9.54 g or 18.5%) were observed with ENS when expressed as g of CH<sub>4</sub>/kg of forage dry matter intake (fDMI) (<italic>P</italic> = 0.037). Lower concentrations of NH<sub>3</sub>-N and a higher ruminal pH were observed in ENS groups 6 h after supplementation (<italic>P</italic> &lt; 0.05). Total VFA rumen concentration 6 h (<italic>P</italic> = 0.009) and 12 h after supplementation with EN resulted in lower acetate concentrations in the rumen (<italic>P</italic> = 0.041). Steers supplemented with EN had a greater ruminal abundance of <italic>Bacteroides, Barnesiella, Lactobacillus</italic>, <italic>Selenomonas, Veillonella, Succinimonas, Succinivibrio</italic>, and <italic>Duganella</italic> sp. (<italic>P</italic> &lt; 0.05), but a lower abundance of <italic>Methanobrevibacter</italic> sp. (<italic>P</italic> = 0.007). Strong negative correlations were found between daily methane emissions and Proteobacteria, Erysipelotrichaceae, Prevotellaceae, and <italic>Roseburia</italic>, <italic>Kandleria</italic>, <italic>Selenomonas</italic>, <italic>Veillonella</italic>, and <italic>Succinivibrio</italic> sp. (<italic>P</italic> &lt; 0.05) in the rumen of ENS steers. Encapsulated nitrate is a feed additive that persistently affects enteric methane emission in grazing steers, thereby decreasing <italic>Methanobrevibacter</italic> abundance in the rumen. In addition, ENS can promote fumarate-reducer and lactate-producer bacteria, thereby reducing acetate production during rumen fermentation.</p>