Food deprivation and feeding of broiler chickens is associated with rapid and interdependent changes in the somatotrophic and thyrotrophic axes

Abstract

1. In several experiments, hormonal changes in the somatotrophic axis, growth hormone (GH) sensitivity to a GH-secretagogue, thyroid hormones and their metabolising enzymes and plasma glucose levels were measured in relation to food deprivation and reinitiation after a single daily meal in 4- to 5-week-old male broiler chickens. 2. Floor-reared male broiler chickens were fed ad libitum or were restricted to a daily food intake of 40 or 45 g per d from the age of 2 weeks onwards. The daily food allowance was consumed in 0.5 h. 3. Food deprivation increased plasma GH concentrations but decreased GH-dependent variables such as plasma insulin-like growth factor-I and 3,3',5-triiodothyronine (T 3 ) concentrations. Hepatic inner ring deiodinating type III activity was markedly elevated, presumably as a consequence of low hepatic GH receptor numbers, and is thought to be the causal mechanism for the low plasma T 3 concentrations. Food intake reversed these variables in a time-related manner. 4. GH pulsatility characteristics, as calculated by deconvolution analysis, revealed profound changes between food restricted and ad libitum fed animals. Chickens deprived of food for about 23.5 h were characterised by an enhanced pulsatile GH release as reflected in the higher GH secretory burst amplitude, GH mass per burst, GH production rate and GH pulse frequency . These variables returned very quickly to normal values after refeeding. 5. In summary, these experiments taken together demonstrate very clearly the interdependent and timerelated changes of the somatotrophic and thyroid axes upon a single meal in previously food-deprived broiler chickens.