Effects of diet and antibiotics on ruminal fermentation and subacute acidosis in cattle

摘要

A study was conducted to determine the effects of virginiamycin (VM, 175 mg/d) and monensin plus tylosin (MT, 250 and 100 mg/d respectively) on ruminal nitrogen metabolism. Six ruminally cannulated steers were fed corn-based finishing diets with (CORN/WCGF) or without (CORN/SBM) wet corn gluten feed. Ruminal samples were collected to monitor pH, fermentation products (VFA, NH3, AA, and peptides), and ciliate protozoa. Ruminal protease and deaminase activity were measured in vivo by infusing solubilized casein into the rumen and monitoring fermentation products. VM inhibited deaminase activity as evidenced by increased concentrations of AA after casein dosing compared to MT and control. The protein in CORN/WCGF appeared more ruminally degradable than CORN/SBM.;An experiment was conducted to determine if subacute ruminal acidosis could be induced in five ruminally cannulated and lactating Holsteins using a 50:50 forage: concentrate diet either deficient in eNDF or with increased starch availability. Ruminal pH, fermentation products, and ciliate protozoa were monitored. Acidosis (pH < 5.6 at each sampling time throughout day) was induced on the third day of dietary challenge in cows receiving the diet deficient in eNDF. Means for total organic acid concentrations in both groups were similar throughout the study and pH was likely different due to differing buffering capacities within the rumen.;The effect of ciliate protozoa and added dietary fat were evaluated in eight ruminally cannulated Holstein steers. pH, fermentation products and ciliate protozoa were monitored prior to and during an induced subacute ruminal acidosis challenge. Treatments included ruminal defaunation (no ciliates) or faunation with a dry-rolled corn and wheat finishing diet with or without 6% added dietary fat (tallow). Dietary fat addition tended to decrease protozoa counts prior to challenge. Acidosis (pH < 5.6) was induced in all steers on the first day of challenge, but steers receiving tallow rebounded above pH 5.6 prior to the second day of challenge. After the second day of challenge, all steers were acidotic and remained acidotic through the end of sampling. The addition of tallow to a corn and wheat finishing diet had a small influence on ruminal pH during an acidosis challenge.