PSXI-10 Influence of monensin in the diet of temperate and tropically adapted cattle on the ruminal and fecal metabolome and microbiome

Abstract

Abstract The effect of monensin on the ruminal and fecal metabolome and microbiome of temperate and tropically-adapted cattle (264±6 kg BW) consuming Tifton bermudagrass hay plus a supplement was evaluated. During Period 1, 10 Angus, 10 Brahman, and 10 BrahmanXAngus steers were fed Tifton bermudagrass hay ad libitum for a 21-d period with 5 steers per pen within breedtype at the conclusion of which rumen fluid (100-to-250 mL) and fecal samples were collected and stored at -80C. During Period 2 all steers were fed Tifton bermudagrass hay ad libitum plus 1.185 kg of supplement (908 g corn, 217 g soybean meal, 60 g dried molasses) with or without monensin (220 mg·steer−1·d−1) individually for 21 d. Rumen fluid and fecal samples were stored at -80C until DNA was extracted and total prokaryotes, methanogens and fungi determined by qPCR. Rumen and fecal samples were extracted to quantify short chain fatty acids (SCFA) and monensin content by GC and LCMS, respectively. After 21 d of consumption of bermudagrass hay, neither rumen nor fecal prokaryotic copy number, fungal copy number, nor methanogen copy number differed among breedtypes. The rumen, but not fecal, fungi:bacterial ratio was least for Angus (0.77) and similar between Brahman (1.31) and BrahmanXAngus (1.21) steers (P < 0.0032). Ruminal SCFA concentrations were similar among breeds as was the acetate:propionate ratio (Angus: 3.52; Brahman: 3.64; BrahmanXAngus: 3.43). Monensin was not detected in control rumen fluid but averaged 363±24 ng/mL for monensin steers. Monensin reduced the acetate:propionate ratio (P < 0.001) by 18, 25.1, and 18.4% for the Angus, Brahman, and BrahmanXAngus steers, respectively. Rumen prokaryotic copy number (P < 0.10), methanogen copy number (P < 0.035), and methanogen:prokaryote ratio (P < 0.001) were reduced within each breedtype by monensin. Addition of monensin reduced methanogen copy number and improved utilization of the diet in temperate and tropically-adapted beef cattle.