Master of Science / Department of Animal Sciences and Industry / James S. Drouillard / Ruminal characteristics and feedlot performance were measured for steers adapted to a high-grain diet using a traditional 22-d step-up program (Control) and for steers adapted over 10 d with the aid of M. elsdenii NCIMB 41125 fresh culture administered as an oral gavage (Fresh), an oral gavage of rehydrated lyophilized culture (Rehyd), or Rehyd combined with lyophilized culture powder administered daily as a ration top-dress (Rehyd+Daily). Yearling steers (n = 435; initial BW = 408 ± 5 kg) were blocked by weight and randomly allocated to 64 concrete surfaced pens with 7 steers/pen and 16 pens/treatment. Step-up diets contained 40, 30, and 20% corn silage, and were followed by a finishing diet containing 10% corn silage and 90% concentrate. Ruminal fluid was obtained from a subset of steers by rumenocentesis 26 h after their first feeding, and inoculated into culture tubes containing lactate medium to determine differences in capacity for lactate metabolism over 24 h. A radiofrequency pH bolus was placed in the reticulorumen of 32 steers, that measured ruminal pH every 10 min for 124 d. Steers were fed once daily ad libitum for 156 d, then weighed, and transported 450 km to a commercial abattoir for harvest. HCW and incidence of liver abscesses were determined at harvest and carcass traits were evaluated after 36 h of refrigeration. No differences were detected for feedlot performance (P > 0.20), liver abscesses (P = 0.45), or carcass traits (P > 0.20). Capacity for lactate utilization was increased with all forms of M. elsdenii, as evidenced by increases in optical density (absorbance) of M. elsdenii cultures, disappearance of lactate, and increase in butyrate production (P < 0.01). Steers on Rehyd and Rehyd+Daily treatments spent less time between pH thresholds of 5.6 > pH > 5.2 (P < 0.01); 5.2 > pH > 5.0 (P < 0.01); and pH < 5.0 (P < 0.01) than Controls throughout the finishing period. In conclusion, steers dosed with M. elsdenii can be stepped up to finishing diets in 10 d with no adverse effects on performance. Ruminal fluid containing fresh cultures or freeze-dried and rehydrated cultures of M. elsdenii NCIMB 41125 were equally effective in metabolizing lactic acid. Lyophilized M. elsdenii resulted in less time below important pH thresholds, but no further benefit of daily administration was realized in this experiment.

Doctor of Philosophy / Department of Animal Sciences and Industry / J. S. Drouillard / Four experiments were conducted to evaluate the potential for accelerating adaption to high-concentrate diets and improving the health of high-risk calves, by administering an oral dose of Megasphaera elsdenii. Lactipro, a probiotic containing a live culture of Megasphaera elsdenii (10[superscript]9 CFU/mL), was orally dosed to cattle (100 mL) at initial processing. In experiment 1, heifers were adapted to a high-concentrate diet in 21 d without Lactipro or dosed with Lactipro and adapted in 16 d, 11 d, 6 d, or fed the high-concentrate diet d 1. Accelerating adaptation decreased DMI (P = 0.09), ADG, and efficiency (P < 0.05) during the first 30 d compared to cattle adapted over 21 d. Over 129 d, DMI and ADG were not different (P ≥ 0.12), but efficiency tended (P = 0.08) to be better for cattle adapted over 21 d. Liver abscesses and carcass traits were not different between treatments, with the exceptions of LM area (quadratic, P < 0.01) and marbling (linear, P = 0.07), which tended to increase with accelerated adaptation protocols. In experiment 2, cattle dosed with Lactipro and placed directly onto the finishing diet required less roughage (P < 0.01), tended to have lower DMI (P = 0.07), better quality grade (P ≤ 0.07), and similar ADG and efficiency (P ≥ 0.14) compared to cattle adapted over 18 d without Lactipro. Over the first 24 d DMI, DM fecal output, and apparent total tract NDF digestibility were greater (P < 0.01) for cattle adapted over 18 d. In Experiment 3, dosing calves, of Mexican origin, with Lactipro did not affect performance (P ≥ 0.16). Second antibiotic therapies for undifferentiated bovine respiratory disease (UBRD) tended (P = 0.06) to be lower in calves dosed Lactipro. In Experiment 4, dosing calves from Texas with Lactipro increased DMI, ADG, and efficiency (P ≤ 0.05). The incidence of 1st and 2nd antibiotic therapies for UBRD (P < 0.01) and medical cost were decreased for calves dosed Lactipro (P < 0.05). Dosing cattle with Lactipro allows for accelerated adaption to high-concentrate diets, decreases reliance on roughages, and improves health during the receiving period.