Effects of castration, with and without testosterone replacement, on leg bone integrity in the domestic fowl

Studies were conducted to assess the effects of castration on leg bone integrity of male White Leghorn chickens. Eighteen 5-week-old males were randomly allocated to 3 groups: group 1--intact controls, group 2--castrated, and group 3--castrated and subsequently treated with testosterone (T)-filled Silastic capsule implants. Body weight and plasma concentrations of luteinizing hormone, androgens, and total calcium were measured in each bird at intervals throughout the experiment. Subsequently, radiographs were performed upon the tibiotarsus-tarsometatarsus region of the left limb of birds from the 3 treatment groups at 7, 35, and 47 weeks of age and assigned a score of 1 to 3 (1 = normal; 3 = greatest pathologic change). Analysis of radiologic scores indicated that at 35 and 47 weeks, castrated birds (group 2) had a mean score significantly greater than that of control birds (group 1). The abnormality was typified by hyperossification with exostoses in the ossified tibial cartilage and lateral calcaneal ridge. In contrast, radiologic scores from individual T-implanted castrated birds (group 3) at 35 and 47 weeks were more variable, but the mean score was not statistically different from that of the control group. We conclude that the depression of circulating concentrations of sex steroids, by castration, in young male chickens results in hypercalcification of the tibiotarsus-tarsometatarsus region of the limb. This effect appears to be mediated directly or indirectly by T or a metabolite of T.