Leg Deformities: Inability to Increase Severity by Increasing Body Weight of Chicks and Poults

Abstract

Five 4-week experiments were conducted to determine the effects of body weight on the severity of leg deformities in broiler chicks and turkey poults reared on raised wire floors. In order to make the influence of body weight independent of genetic, environmental, and nutritional effects, increasing body weight was achieved by harnessing steel weights on the backs of poults and chicks. In the first experiment, 3-day-old male and female chicks were harnessed with 0-, 1-, 2-, or 3-g weights (nine chicks per weight load). Weights were changed every 3 to 4 days until 4 weeks of age such that the artificial weight averaged 0, 3, 4.5, or 8.5% of their body weight. In Experiments 2 and 3, three replicates of 10 female chicks were assigned to isocaloric diets containing 18, 21, or 24% crude protein. Five chicks in each treatment and replicate were harnessed at 3 days of age with weights averaging approximately 13% of their body weight. Weights were changed weekly. Experiments 4 and 5 were designed similar to Experiments 2 and 3 except that male and female turkey poults were fed 22, 25, or 28% dietary crude protein and were harnessed with weights equal to about 8 to 10% of their body weight. Body weights of the birds were recorded weekly. Condition of the birds’ legs was scored weekly by a subjective method where: 0 = normal, 1 = slight deformity, 2 = moderate deformity, 3 = severe deformity, and 4 = completely crippled; and by an objective measurement where degree deviation of the tarsometatarsus from the line of the tibiotarsus was measured using a protractor. Artificial weight loading had no effect on weekly body weights of chicks in Experiment 1 or poults in Experiments 4 and 5 but tended to decrease body weights of chicks fed 18 and 21% crude protein at 24 and 31 days of age in Experiment 2 and 24- and 31-day-old chicks fed 18% crude protein in Experiment 3. Decreasing dietary crude protein reduced body weights at 7, 14, 21, and 28 days of poults in Experiments 4 and 5 but had little or no affect on chick body weight in Experiments 2 and 3. Artificial weight loading had no consistent affect on die severity of leg deformities in all experiments when evaluated both objectively and subjectively. Decreasing body weight by decreasing dietary crude protein had no effect on the severity of leg deformities. In conclusion, the severity of leg deformities appears to be independent of the bird's body weight.