Degree Type


Date of Award


Degree Name

Master of Science


Animal Science


Animal Science

First Advisor

Hugo A. Ramirez-Ramirez


Forty-eight multiparous Holstein cows (121 ± 22 DIM) were used in a randomized complete block design to evaluate supplementation of two probiotic strains Pediococcus acidilactici 19839 (PED) or Bacillus subtilis 15541 (BAC) on the effect of milk yield and composition, total tract nutrient digestibility, rumen pH and volatile fatty acid concentration. Cows were housed in a free-stall barn, milked three times a day, and fed twice daily for 105 d. All treatments consisted of a basal TMR diet, top-dressed with a specific supplement: 1) control (CON) with no probiotics; 2) PED fed at 1 × 1010 CFU/d; 3) BAC fed at 1 × 1010 CFU/d and; 4) basal TMR supplemented with a combination of Enterococcus faecium at 1 × 1010 CFU/d and yeast (PRO). Individual feed intake and milk yield data were recorded daily and averaged weekly. Two blocks contained rumen fistulated cows and were used for rumen pH measurements and rumen fluid collection on d 105. Data were analyzed using a mixed model with week, treatment and their interaction as fixed effects with pre-experiment milk yield as a covariate and cow and block as random effects. Dry matter intake was similar across treatments with an average of 24.3 ± 0.8 kg/d. Milk yield averaged 37.4 ± 1.4 kg/d across treatments; analyses of data in 5-wk periods showed that PED resulted in additional 3.9 ± 2.9 kg/d for the first period compared to all other treatments. Concentration of milk fat and protein were similar across treatments with averages of 3.63 ± 0.02 % and 3.05 ± 0.06 %. Digestibility of dry matter, organic matter, and protein were similar across treatments and averaged 66.65 ± 1.48 %, 68.88 ± 1.43 %, and 67.11 ± 1.81 %. Similarly, acid and neutral detergent fiber digestibility was similar for all treatments. Mean daily rumen pH was 5.69 ± 0.05 across treatments. Proportions of acetate, propionate and butyrate averaged 57.1 ± 1.8%, 26.6 ± 2.3% and 11.1 ± 0.7%, across treatments respectively. Although the mechanism for transient increase in milk yield remains to be elucidated, the results demonstrate that, in dairy cattle, supplementation with the specific strain P. acidilactici 19839 has the potential to improve lactation performance without detrimental effects on digestibility, rumen pH, and VFA concentration.


Copyright Owner

Ashley Dawn Thomas



File Format


File Size

45 pages