Date of Award


Degree Type


Degree Name

Bachelor of Science (BS)


Animal, Dairy, and Veterinary Sciences

First Advisor

Dr. Jong-su Eun


The aim of the present study was to assess characteristics of in vitro ruminal fermentation when mixed cultures were offered lactation dairy diets supplemented with the direct-fed microorganism, Propionibacterium P63 in continuous cultures. The design of the experiment was a 2 × 2 factorial with 4 replications. Diets based on corn silage and alfalfa hay as the forage sources were formulated; high forage (HF) or low forage (LF) diet with a forage-to-concentrate ratio of 60:40 or 40:60 (DM basis), respectively, was combined without or with P63 to form 4 treatments: HF without P63, HF with P63, LF without P63, and LF with P63. Approximately 700 mL of the strained ruminal fluid obtained from 2 lactating dairy cows was inoculated into each of 4 fermentors with a continuous dual-flow system. The cultures were allowed 6 d of adaptation to the treatments followed by 3 d of sampling and data collection. Feed totaling 40.0 g of DM was added to each fermentor daily in equal portions delivered at 0800 and 2000 h. The P63 treatments received 7 × 108 cfu of P63/fermentor/feeding. Supplementing P63 decreased culture pH (P = 0.05) in the LF diet, but not in the HF diet. Feeding the LF diet increased total VFA concentration compared with the HF diet (P = 0.01), and supplementing P63 increased total VFA concentration regardless of level of forage in the diet (P < 0.01). Molar concentrations and proportions of acetate and propionate did not differ in response to supplementing P63 in the HF and the LF diet. However, molar concentration and proportion of butyrate increased due to P63 supplementation (P < 0.05) only in the LF diet, resulting in interactions between level of forage and P63 supplementation (P < 0.08). Overall results in this in vitro study indicate that P63 supplementation enhanced ruminal fermentation by increasing VFA production, but its impacts on continuous culture fermentation differed between the HF and the LF diet.