Effects of monensin and Lasalocid on Fermentation of amino acids in vitro by mixed ruminal bacteria

The objective of this experiment was to study the in vitro effects of the ionophores on ruminal fermentation of amino acids. Rumen fluid of a steer fed an elephant-grass based diet was used in the incubations, with addition of casein hydrolysate, in three treatments (control-C; monensin-M; and lasalocid-L). Inocula were transferred into new tubes. daily and on the 11(th) day of incubation, tubes from each of the treatments were used to inoculate three new tubes (C, M, L), totalizing nine combinations (second phase). From the 1(st) to the loth day of incubation, addition of ionophores prevented increases in ammonia production compared to the control. From the 11(th) to the 12(th) day, the ionophores were more efficient in decreasing ammonia production when they were absent in the first phase, and lasalocid was still capable of decreasing ammonia production and microbial protein concentration when monensin was used in the first phase. From the 16(th) to the 20(th) day, independently of the first phase treatment, the ionophores decreased ammonia production. However, the ionophores decreased microbial protein concentration in tubes that served as control in the first phase, whereas an increase was observed in tubes treated with ionophores in the first phase. Conversely, when the ionophores were removed in the second phase, there was a significant increase in ammonia production, but this effect was not detected on the 11(th) and the 12(th) days, probably due to the residual effect of the ionophores.