Effect of monensin on the crop microflora of broiler chickens

Abstract

Experiments were undertaken to evaluate the effect of monensin on both the microorganisms and their metabolite production in the crop of 3-week-old broiler chickens. The addition of monensin to the feed (100 mg/kg) significantly (P < 0.05) lowered the number of lactobacilli in the crop and decreased the concentration of lactate, acetate, succinate and ethanol in both in vivo and in vitro incubations of the crop contents. The decreased acid production increased the pH of the digesta and also the pH of the monensin-supplemented cultures (P < 0.01). The decrease in the number of lactobacilli was accompanied by a concomitant proliferation of conform bacteria and enterococci. The lactobacilli counts returned to the pretreatment level within 5 days of monensin feeding. The counts of conforms and enterococci, however, remained elevated. The concentration of lactate in the crop was lower and the pH higher in the monensin-fed chickens than in the control chickens (P < 0.005). The microbial metabolite production was lower in all the cultures supplemented with monensin, both in the control incubations and in those inoculated by the crop contents of monensin-fed chickens (P < 0.01). The effect of monensin in vitro ceased after 10 days of monensin feeding to the inoculi donors. In the presence of monensin, the crop environment was more suitable to the proliferation of coliforms, which might be a factor in the increased incidence of nonspecific septicemia.