PSVI-14 Effect of Dietary Nitrates and Sulfates on Enteric Methane Mitigation in Finishing Cattle

Abstract

Abstract A study was conducted to determine the effect of nitrate and sulfate supplementation on cattle performance and methane emissions in finishing diets and to identify the effect of nitrate and sulfate addition on rumen microbiota composition and function. One hundred and thirty one day feeding trial was conducted using 24 head of cattle (initial BW = 918 lb; SD = 79 lb) where the cattle received one of four treatments no supplementation (CON), 2.0% dietary nitrate (NT), 0.54% dietary sulfate (SF) or both (COMBO), with 6 steers per treatment. Performance, volatile fatty acid (VFAs) profile and CH4:CO2 emissions data were analyzed using MIXED procedure of SAS. Rumen samples were collected and analyzed through amplicon sequencing targeting the 16S rDNA gene V4 region. Microbiome richness and composition were analyzed using Qiime2. Microbial genes involved in pathways linked to methanogenesis, nitrate, and sulfate metabolism were identified with metagenomic sequencing. Gene prediction, functional profile and pathway mapping were conducted using KEGG database. In diets with only sulfate or nitrate, diet had no impact on CH4:CO2 emissions, but nitrate and sulfate in combination decreased CH4:CO2. However, a reduction in dry matter intake (DMI) (P < 0.01), average daily gain (ADG) (P = 0.07) and gain:feed (G:F) (P = 0.09) was also recorded. Significant increase in bacterial genera with H2 utilization capability e.g. propionate, lactate forming bacteria e.g. Prevotella, Bacteroides, Megasphaera, Selenomonas, Lactobacillus; nitrate and sulfate reducing bacteria e.g. Selenomonas, Desulfovibrio was observed in COMBO diet. Differential gene abundance in metabolic pathways illustrated decrease of enzymes linked to methanogenesis in COMBO diet. This study provides evidence that methane yield is linked to diet type and differential gene abundance in the cattle rumen microbiome.