bacteria from the Bacillus subtilis group in the rumen when feeding direct-fed Bacillus compared with control. Treatment did not affect ruminal pH, NH3-N, or concentrations of acetate, propionate, and butyrate. However, direct-fed Bacillus increased ruminal concentrations of isovalerate and isobutyrate (tendency). Treatments did not affect lactation performance. Supplying direct-fed Bacillus enhanced milk relative concentration of anteiso 130 by 27.3% and of anteiso 150 by 6.5% and tended to increase concentrations of iso 140 (+41.8%) relative to control. When expressed on a yield basis, direct-fed Bacillus increased the secretion of anteiso 130 and decreased that of 110, 150, 170 (tendency), and cis-9 171. These variations, although limited in magnitude, indicate that milk branched-chain fatty acid composition is sensitive to ruminal microbiota modifications without changes in chemical composition of the diet.
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