"Treatments were yeast culture or control (mix of dry ground corn and soybean meal), top-dressed at 56g per head per day throughout each period. Diets containing dry ground corn grain were fed from day 1 through 26 of each period. On the last 2 days of each period, the dry ground corn was replaced by finely ground high-moisture corn grain on an equivalent dry matter basis to abruptly increase ruminal fermentability of dietary starch. Response variables were averaged for day 25 and 26 for the dry corn treatment and for day 27 and 28 for the high-moisture corn treatment each period. The fermentable starch challenge decreased dry matter intake by 1.9 kg/day and tended to increase milk yield compared with the dry corn diet. However, effects of the fermentable starch challenge on yield of milk fat varied for the yeast culture and control diets; yield of milk fat decreased from 1.42 to 1.30 kg/day for the control treatment but increased from 1.40 to 1.47 kg/day for the yeast culture treatment. Milk fat concentration tended to decrease from 3.34 to 3.03% during the dietary challenge compared with the base diet for the control treatment but was not affected (mean = 3.32%) by the dietary challenge for the yeast culture treatment. An interaction of treatments was also detected for fat-corrected milk, which increased from 41.0 to 43.0 kg/day for the yeast culture treatment but decreased from 41.6 to 39.8 kg/day for the control diet with the fermentable starch challenge. Frequency of ruminating bouts was decreased by yeast culture compared with control (12.8 vs. 15.7 bouts/day) but not the fermentable starch challenge. No treatment interactions were observed for any measure of ruminal pH, total or individual volatile fatty acid concentration in ruminal fluid, acetate: propionate ratio, or individual fatty acid isomers in milk fat," wrote R.A. Longuski and colleagues, Michigan State University.
The researchers concluded, "Yeast culture supplementation may help prevent depression in milk fat during transition to a diet with highly fermentable starch, but the mechanism responsible remains to be elucidated."
Longuski and colleagues published their study in the Journal of Dairy Science ("Yeast culture supplementation prevented milk fat depression by a short-term dietary challenge with fermentable starch." Journal of Dairy Science, 2009;92(1):160-167).
For additional information, contact M.S. Allen, Michigan State University, Dept. of Animal Science, East Lansing, MI 48824.
From the February 2, 2009, Prepared Foods E-dition