Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Michael Arambel


Michael Arambel


George Stoddard


LeGrande Ellis


Ronald Canfiled


Randall Wiedmeier


Four barren Holstein cows fitted with ruminal fistulas were assigned to each of two dietary treatments in a replicated 2 x 2 Latin square design. Treatments consisted of a basal ration and a basal ration plus lOg/d of a viable yeast culture (Saccharomyces cerevisiae). Cows were fed treatments for a 21-day adaptation followed by a 7-day collection period. Total ruminal bacteria, cellulolytic bacteria and protozoa were unaffected by treatment.

Feeding the viable yeast culture significantly increased ruminal acetic acid and acetic/propionic ratio. Molar percentage of propionic, isobutyric, isovaleric and valerie acids and rumen ammonia-N levels were significantly reduced in cattle fed added yeast culture. Liquid dilution and particulate rate of passage and total tract apparent nutrient digestibility were unaffected by treatment. Eighteen Holstein cows in mid-lactation were allocated equally to one of two treatments based on stage of lactation and previous mean daily 2-week milk yield. Therefore, nine cows were allocated to each treatment. Treatments consisted of a basal ration and a basal ration plus 10g/d of yeast culture (Saccharomyces cerevisiae). Cows were fed total mixed rations for a 10-week period. In week 8, feed and fecal samples were collected twice daily for 3 days. Acid detergent fiber insoluble ash was used to determine total tract apparent nutrient digestibility.

Feeding mid-lactation dairy cows the viable yeast culture had no effect on mean daily dry matter intake . However, it tended to improve mean daily 3.5% FCM. Milk production efficiency was higher in lactating dairy cows supplemented with the viable yeast culture when compared to the nonsupplemented cows. Milk composition and overall mean body weights were unaffected by treatment. Total tract apparent nutrient digestibilities also were unaffected by treatment.