Effects of analyzable diet components on responses of lactating dairy cows to Saccharomyces cerevisiae based yeast products: A systematic review of the literature

Abstract

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 ( r 2 = 0.49 and 0.44, respectively), predicted based upon milk production of the control group cows and the chemical composition of the diet. However, the precision of these predictions appeared to be compromised by the unequal allocation of NE l between milk and BW change by the YP fed cows among experiments. Thus, a reduced set of experiments ( i.e., n = 11) in which BW and BW change had been measured, thereby allowing the percentage response in NE l output to feeding of a YP to be calculated, suggests that the percentage increase in NE l output to feeding of a YP will be suppressed in diets with higher NDF and CP levels, although changes will be more positive as the fermentability of the NDF ( i.e., the ADF/NDF ratio in this analysis) decreases. These findings can be interpreted to support the currently proposed mode of action of Saccharomyces cerevisiae YP that they act to stimulate rumen microbes that increase fermentability of fiber, but not to support another currently proposed mode of action that they allow rumen microbes to more effectively metabolize end-products of ruminal starch fermentation. Regardless, overall benefits to feeding Saccharomyces cerevisiae YP on milk and NE l output are modest ( i.e., 2.7 and 5.3%, respectively). Future feeding studies with YP should consider dose response designs at YP feeding levels higher than those used in past studies, as well as report BW and BW change to allow YP response on animal energetics to be assessed.