The effects of increasing aflatoxin B1 concentration (0, 0.75, 1.5 mg/kg) on broilers
with or without necrotic enteritis or virginiamycin were determined. In the 23-d study,
22 male Cobb 500 chicks per pen were allotted to 12 treatments (3 × 2 × 2 factorial
arrangement) with 8 replications. Intestines of 5 birds per pen were examined for
lesions on d 21. Birds were allowed to consume feed and water ad libitum. Aflatoxin
was included in the diets from d 0. All birds received a 10× dose of coccidiosis vaccine
on d 10. Pens of birds where necrotic enteritis was being induced were on Clostridium
perfringens pathogen (CPP) contaminated litter from d 0. Aflatoxin decreased gain
and feed intake and resulted in poorer feed:gain, increased mortality, and higher
lesion scores. Inducing necrotic enteritis increased lesion scores and decreased feed
intake and gain. Adding virginiamycin to the diets improved gain, feed intake, feed
conversion, and decreased mortality. There was a 3-way interaction (aflatoxin × virginiamycin
× CPP) on gain; increasing aflatoxin decreased gain and the effects of CPP and virginiamycin
were dependent on aflatoxin concentration. In the absence of aflatoxin virginiamycin
increased gain but was unable to prevent the growth suppression caused by CPP. At
0.75 mg/kg of aflatoxin virginiamycin no longer increased growth in non-CPP challenged
birds but was able to increase growth in CPP-challenged birds. At the 1.5 mg/kg of
aflatoxin concentration, virginiamycin increased gain in non-CPP-challenged birds
but challenging birds with CPP had no effect on gain. Virginiamycin improved overall
feed conversion with the greatest improvement at 1.5 mg/kg (aflatoxin × virginiamycin,
P < 0.05). Aflatoxin increased lesion scores in unchallenged birds but not in challenged
birds (aflatoxin × CPP, P < 0.001). Aflatoxin and necrotic enteritis decrease broiler
performance and interact to decrease weight gain, virginiamycin helps improve gain
in challenged birds at 0.75 mg/kg of aflatoxin, but not at 1.5 mg/kg of aflatoxin.