The effects of the monensin supplementation on the ruminal parameters and digestibility were evaluated after 120 days of trial, using 20 Holstein bull calves with average weight and age of 90.8 kg and 80 days, respectively. The treatments were 0, .4, .8 and 1.2 mg of monensin/kg LW. As the monensin levels increased the pH values increased (5.97, 6.14, 6.36, and 6.48), but N-NH3 (45.54, 38.08, 28.39, and 24.17 mg%), acetate (36.55, 33.72, 35.62, and 26.35 mM), butyrate (1.22, 7.27, 6.13, and 4.30 mM) and total volatile fatty acids (79.07, 72.,91, 73.44, 58.57 mM) decreased in the rumen. The monensin increased the coefficient of apparent digestibility (GEDC with 50.51, 53.59, 55.89, and 60.43%; DMDC with 59.34, 60.47, 62.37, and 66.38%; CPDC with 73.56, 75.07, 75.92, and 78.31%; NDFDC with 30.64, 31.92, 35.84, and 43.72%; ADFDC with 13.16, 17.25, 22.55, and 31.21% for 0, 0.4, 0.8, and 1.2, respectively) and of the TDN (NDT with 59.12, 60.57, 61.91, and 65.52%; ED with 1776,07; 1884.38, 1965.24, and 2124.79 cal/g; MSD with 59.34, 60.47, 62.37, and 66.38%; PD with 14.35, 14.64, 14.81, and 15.27%; DNDF with 10.65, 11.10, 12.46, and 15.20%for 0, 0.4, 0.8, and 1.2, respectively). Monensin positively influenced the studied ruminal parameters, improving the feed digestibility.
ammonia; calves; digestible nutrients; ionophores; pH; volatile fatty acid
