In vivo tetracycline labelling as a measure of rearing-system influence on chicken-bone dynamics

The objective of this study was to estimate the internal dynamics of leg (tibia) and wing (humerus) bones in light and heavy types of chicken, reared in cages and on the floor. The ratio of floor-to-cage area was 3:1. All chicks were fed a standard broiler mixture (0-4 weeks with 0.9% Ca and 0.7% P; 4-7 weeks with 0.8% Ca and 0.5% P). Each bird was given two intraperitoneal injections of 30 mg/kg of oxytetracycline at 2-day intervals. The results showed no significant differences between floor- and cage-reared birds in tibial-osteon appositional rates. However, there was a significant rearing-system effect on humerus internal dynamics. Seven-week-old light chicks, reared on the floor, had humeri with a higher appositional rate than those reared in the cages.