Long-term hypothyroidism causes decreased bone competence in male European starlings, Sturnus vulgaris

Male European starlings were thyroidectomised and held on either short or long day photoperiods. Intact euthyroid control birds were also held on either short or long days to control for differences in reproductive condition. Femora of birds from each group were sampled following plasma thyroxine measurement. Hypothyroidism caused decreased bone mechanical competence in starlings, as determined by Vickers microhardness testing. It was also found that transfer from short to long daylengths caused increased plasma thyroxine concentration, but that this did not affect bone mechanical competence. The finding that hypothyroidism causes decreased bone mechanical competence agrees with another animal study and a number of human studies, and we conclude that bone quality and mechanical competence can be adversely affected by abnormal thyroxine concentrations.