Effects of a supplemental liquid yeast product on feed intake, ruminal profiles, and yield, composition, and organoleptic characteristics of milk from lactating Holstein cows.

A liquid yeast product (about 11% DM), produced as a by-product of riboflavin synthesis, was incorporated into a TMR at three concentrations to determine the maximal inclusion rate and acceptability as a feed supplement in diets of lactating cows. Twelve Holstein cows in midlactation were randomly assigned to TMR treatments containing (as-fed basis) 1) no yeast product (control), 2) 20% dietary yeast product, or 3) 40% dietary yeast product in a 3 x 3 Latin square design with 3-wk periods. Dietary DM contents were 90, 74.2, and 58.4% for the 0, 20, and 40% yeast product TMR, respectively. The control TMR was based on a 45:55 ratio (DM basis) of mixed concentrate and chopped alfalfa hay. The DMI decreased linearly with increasing percentages of dietary yeast product. Milk yield and milk protein percentage were not altered by inclusion of the dietary yeast product. Milk fat tended to respond quadratically to increases in the percentage of dietary yeast product in the TMR. The supplemental dietary yeast product had no effect on ruminal pH; however, the ratio of acetate to propionate decreased, and propionate percentage tended to increase, as supplementation of the yeast product increased. Addition of yeast product to the TMR had no adverse effect on milk flavor. Milk from cows fed yeast product had better flavor than milk from control cows. Results indicate that inclusion of this yeast product at 40% depressed feed intake.