Effects of dietary roxarsone supplementation, lighting program, and season on the incidence of leg abnormalities in broiler chickens.

Two 4 x 2 factorial experiments were designed to test the effects of four diets, differing in anticoccidial programs and roxarsone (3-nitro-4-hydroxyphenylarsonic acid) content, and two lighting programs on the incidence of leg abnormalities in 56-d-old male and female broiler chickens. The four diets were: A) basal diet + salinomycin (60.0 g/ton); B) basal diet + salinomycin (60.0 g/ton) + roxarsone (45.4 g/ton); C) basal diet + roxarsone (45.4 g/ton) + live coccidial vaccine; and D) basal diet + live coccidial vaccine. The light treatments were: 1) restricted (R) [18 h light (L): 6 h dark (D)] and 2) standard (S) [23L:1D]. The respective experiments were conducted during winter (Experiment 1, November to January) and summer (Experiment 2, June to August) growing conditions in the southeastern U.S. Light treatment had no significant (P > 0.10) effect on the incidence of leg abnormalities in either experiment. However, in Experiment 1, there was a light treatment by sex interaction; leg abnormalities were greater for males on Treatment R than Treatment S. In Experiment 2, females had a higher incidence of leg abnormalities than males (8.29 vs 4.73%). There was a diet by sex interaction for the incidence of leg abnormalities in Experiment 2; females had a greater incidence of leg abnormalities than males on Treatment A. In both experiments, the incidence was greater with dietary treatments containing roxarsone (P < 0.10). The percentage of leg abnormalities was greater in Experiment 2 than Experiment 1. Leg abnormalities were primarily due to fibrosis of the gastrocnemius tendons and tendon sheaths.