The objective of this trial was to study the in vitro effects of monensin and propolis on ruminal fermentation of amino acids. Ruminal fluid was collected from a steer grazing tropical pasture and after addition of casein hydrolysate was used in the incubations. Treatments consisted of: control-C; monensin-M; and propolis-P. In the first phase of the study, inocula were transferred daily into new tubes until day 10; on the 11th day of incubation, tubes from each of the treatments were used to inoculate three new tubes (C, M, P) yielding nine combinations that were also transferred daily and incubated for nine days (second phase). From day one to day 10 of incubation (first phase), addition of ionophore and propolis prevented increase in ammonia production compared to the control. Propolis was more efficient in decreasing ammonia production than monensin in the first phase and it was also able to decrease ammonia production and specific activity of ammonia production (SAAP) in the second phase regardless of the first phase treatments; monensin was as efficient as propolis, in the second phase, when the inhibitors were absent in the first phase. It was observed a significant increase in ammonia production with monensin by removing the inhibitors in the second phase
ammonia; bacteria; monensin; propolis; rumen
