Characterization of plasma hormone levels and lipogenic enzyme activity in chickens divergently selected for oxygen consumption.
The bases for differences in growth and metabolism of lines previously selected for divergence in O2 consumption in comparison to a randombred control population were studied. Body weights, carcass fat, plasma growth hormone (GH), triiodothyronine (T3), thyroxine (T4), malic enzyme, and citrate cleavage enzyme activities were determined. The early growth of the low O2 birds was greater than the high O2 birds, whereas the growth rate of the control population was intermediate to, but not statistically different from, the two O2 lines. Six-week body weights did not differ between the lines. Percent fat of the high O2 birds was less than the other two lines at 1 and 2 weeks of age but greater than the low O2 birds at 3 weeks of age. Percent fat did not differ between the lines at 6 weeks. Plasma T4 levels differed between the lines only at Day 1, when the control population exhibited greater T4 levels than the O2 lines. Plasma T3 levels were lower in the high O2 chicks in comparison to only the control chicks at 0, 1, and 2 weeks of age. No line differences in T3 levels were detected at 3 or 6 weeks. From 1 to 3 weeks, GH levels were greater in the low O2 birds than the high O2, while the control birds had GH levels intermediate to the O2 lines. By 6 weeks, the O2 lines had similar GH levels, but these levels were lower than those of the controls. No consistent line differences in malic enzyme or citrate cleavage enzyme activities were observed.