Publication Date


Degree Program

Department of Agriculture

Degree Type

Master of Science in Animal Science


Livestock have been fed yeast as a feed supplement for more than 100 years Stone, C. 00). Yeast is a microscopic, single cell fungi of the plant kingdom. Of the 50,000 species of fungi, only 60 different genera of yeast representing about 500 different species exist. A few of these are used commercially in the animal feed industry as active dry yeast or yeast culture (Kreger, van Rij, 1984). Yeast culture consists of live yeast cells, plus the medium on which yeast is grown. Yeast products are commonly fed as pro-biotics, but little is known about their effects. Some studies have reported that yeast products increased milk yield and milk fat percentage; however, other studies found that yeast products had no effect on any of these factors (Middelveld. H 1998). A three phase trial, starting August 2003 and ending February 2005, was conducted at the Western Kentucky University Agricultural Research and Education Complex (Dairy facilities), in Bowling Green, Kentucky. Trial 1 evaluated the affect of dietary yeast, (WY) a, fed to cows in early lactation during heat stress conditions. Trial 2 evaluated the effect of dietary yeast WY fed to pre and post-partum cows during weather stress conditions. Trial 3 evaluated milk yield of cows fed post-partum cows 2 different types of yeast, (CC5)b or (YS)C, versus a no yeast control group (CG)d, during weather stress conditions to post-partum cows. Cows in trials 1 and 2 were fed a total mixed ration (TMRs) consisting of corn silage, alfalfa hay and haylage, grain mix, whole cottonseed and controlled access to alfalfa pasture; while the third trial cows received a TMR of corn silage, alfalfa hay, whole cottonseed and grain mix. In all trials, milk weights were captured and recorded at each milking using electronic weigh meters, which download into a computer. Seven day average milk weights were used for the analysis in all the trials. Data were analyzed using SPSS 13 and Microsoft Excel XP 2006, standard statistical analysis software. In trial one milk yield and energy corrected milk (ECM)were statistically higher (p<0.05) in the Holstein WY group. The limited Jersey sample size did not provide adequate statistical data for analysis. In the second trial, milk yield and ECM were statistically higher in the Jerseys in trial WY versus the Jerseys in the CG group. There was no significant statistical difference in Holsteins treated WY versus the Holsteins in the CG group. In the third trial, ECM was statistically significant at (p= 0.05) in the CC5 groups versus the CG group. The CC5 group differed from YS group at the (p= 0.05) level in the Holstein groups as well as in the Jersey groups. The statistical difference in ECM may be due to the different composition of the yeast used in the diet plus the stress caused by environment. The CC5 group and YS groups were statistically higher in average milk yield (p=0.05) han the CG group. A positive response on milk yield appears to be found in those groups feed yeast. Based on these completed trials, the usage of yeast has a moderate impact on milk production as well as milk composition. These heat and transition trials suggest positive economical returns based on ECM from the usage of yeast.


Animal Sciences | Dairy Science

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