Physiological responses to divergent selection for phytate phosphorus bioavailability in a randombred chicken population.

An investigation was conducted to study insulin-like growth factor (IGF)-I, IGF-II, insulin, glucagon, leptin, triiodothyronine (T(3)), and thyroxine (T(4)) levels in a chicken population divergently selected for P bioavailability (PBA). There were differences in growth and feed efficiency between the 2 lines. Concentrations of IGF-I, IGF-II, and T(3) were significantly greater in the high PBA line compared with the low PBA line, whereas the reverse was true for glucagon. There were no correlations between IGF-I and II and PBA in either line, suggesting that the line differences may be the result of factors other than PBA. Glucagon and IGF-I have different relationships with feed conversion ratio in the high PBA line compared with the low PBA line. There was a significant correlation between PBA and T(3) in the low line and between PBA and T(4) in the high PBA line. Thyroid hormone levels may be an indirect indicator of PBA in growing chickens. The genes in the thyroid hormone pathway may be key in the identification of genes associated with PBA.