Feeding experiments that used lactating Holstein cows, from peer review publications since 1990, were used to determine the ability to predict production responses of lactating dairy cows to feeding Saccharomyces cerevisiae yeast products (YP) based upon the composition of their diets in a systematic review of the literature. The
22 published experiments reflected 6 YP, with one being used in 7 experiments, 2 in 6 experiments each, and 3 in one experiment each. There were analytical (i.e., neutral detergent fiber (NDF) and starch) differences (P<0.05) in the diets fed, and milk yield, milk energy output and milk fat proportion differences (P<0.05) among
the control group cows of the experiments of the 3 major (based upon numbers of published studies) YP. However, the proportional milk, milk component, milk energy and dry matter (DM) intake response of the cows to feeding of the 3 major YP did not differ.
Simple correlation coefficients of the combined data set (i.e., n = 22) suggested that higher diet NDF or acid detergent fiber (ADF) levels reduced the production response to feeding any YP, while higher diet starch level had little impact. Increased milk and milk energy output of the control cows reduced productive benefits of feeding a YP, and results suggest that the YP milk yield response was absolute
(about 0.9 kg/cow/d) and that it decreased proportional to control group milk yield as control group milk yield increased. Multiple
correlation analysis showed that only milk output and milk protein output response to feeding a YP could be acceptably, but modestly.