THE EFFECT OF PHOTOPERIOD AND FOOD-INTAKE ON DAILY CHANGES IN PLASMA CALCITONIN IN BROILER BREEDER HENS

The roles of photoperiod, energy balance, and concentrations of plasma total calcium (Ca-T) on daily changes in plasma calcitonin (CT) were investigated in broiler breeder hens (84-100 weeks old). In the first study, broiler breeder hens (n = 24), reared on 14L:10D, were divided into two groups. One group was transferred from a restricted diet (DR) of 150 g/day to ad libitum (AL) for 14 days, while the other group re mained on DR. After 2 weeks of an libitum feeding, birds from each gro up (AL and DR) were bled every 2 hr for 24 hr for measurement of plasm a Ca-T and CT. In a second study, the hens (n = 20) were transferred t o continuous light (LL) for 30 days. After the 30 days, food was remov ed from one group for 48 hr prior to blood sampling for 24 hr at 3-hr intervals. In a third study, birds were transferred to an ahemeral lig ht cycle (11L:1OD) for 28 days. Food was removed from the birds (n = 1 1) for 48 hr prior to blood sampling every 3 hr for 24 hr. Four weeks later the same birds were bled again for 24 hr, but this time the bird s were maintained on a restricted feeding schedule. Plasma CT was meas ured by a specific heterologous electrochemiluminescent (ECL) assay wh ile plasma Ca-T was measured by atomic absorption. The results showed that plasma CT concentrations did not correlate with plasma Ca-T conce ntrations. Comparisons made between initial and final Ca-T and CT conc entrations indicated an effect of stress due to repeated handling of t he birds. Concentrations of plasma CT were significantly reduced in th e fasted animals (P < 0.05) compared to diet-restricted controls. Ther e was a significant increase in plasma CT during the dark period of fe d animals which was abolished in animals maintained on LL or fasted. I n conclusion, a surge in plasma CT requires that the hens be provided food and that they be exposed to a dark cycle. (C) 1997 Academic Press .