Effects of Monensin, Virginiamycin and Sodium Bicarbonate on Ruminal Fermentation and Acid-Base Status in Sheep

Four ruminally canulated sheep (55+/-10 kg initial BW) were used in a 4x4 Latin square design to evaluate the effects of monensin, virginiamycin and sodium bicarbonate on ruminal fermentation and acid-base balance in sheep fed a diet with 60% concentrate (DM basis). Treatments included control, monensin (25 mg d(-1)), virginamycin (15 mg d(-1)) and sodium bicarbonate (10 g d(-1)) intraruminally. Each period included 14 d of adaptation and 4 d of sample collection. Ruminal fluid samples were collected at 0, 2,4, 6, 8 and 10 h after the additive dose. Blood samples were collected at 0 and 6 h to determine pH, HCO3, pCO(2), base excess, electrolytes (Na+, K+, Cl-) and other metabolites (glucose, urea, L-lactate, NEFA). Intake was increased (p<0.05) with virginiamycin in comparison with sodium bicarbonate. Addition of sodium bicarbonate reduced significantly (p<0.05) DM intake. Sheep with monensin showed increased proportion of propionate at time of feeding, while virginiamycin lowered percentage of acetate in rumen liquor sampled 10 hours after feeding. Protozoa counts were not affected by the additives. Monensin, virginiamycin or sodium bicarbonate did not affected acid base status in sheep.