Characterization of a sustained-release estrogen implant on oviduct development and plasma Ca concentrations in broiler breeder chicks: modulation by feed restriction and thyroid state.

The effect of estradiol-17 beta (E2) given as a sustained-release implant (Compudose 200) on concentrations of plasma calcium (Ca) and the development of the chick shell gland has been investigated in food-restricted and thyroid hormone-treated 6- to 8-week-old broiler breeder pullets. Chicks implanted with 0, 0.5, 1.0, 1.5, 2.0, and 3.0 Compudose pellets for 24 days (n = 6/group) revealed a dose-response relationship between plasma E2 and Ca and on oviduct growth. Plasma E2 concentrations were characterized by an initial burst phase for approximately 17 days, followed by a constant release phase. Histologic examination of shell gland tissue confirmed the dose related E2-induced development of microvilliated epithelium and tubular glands over time. Feed restriction initiated at 2 weeks of age markedly increased the response to the E2 implants. Birds (n = 8/group) implanted with 2 pellets and feed restricted had increased plasma concentrations of E2 and Ca, and increased growth of the oviduct (P less than 0.01) as compared to ad libitum implanted birds. In a separate study birds (n = 6/group) had restricted access to feed from 8 weeks of age and were implanted with 0, 2, 4, or 8 pellets. At intervals from 9 to 45 days after implantation one bird from each group was killed. Although concentrations of plasma Ca were significantly greater in feed-restricted birds (P less than 0.01), oviduct growth was only marginally increased by the food restriction program. Plasma Ca concentrations in broiler breeder pullets (n = 8/group) implanted with 1 or 3 pellets and injected with T3/T4 (100 micrograms/day) were significantly decreased (P less than 0.05). Injection of thyroid hormone also marginally decreased shell gland epithelial cell height (P less than 0.05) and development of microvilli (P less than 0.05). There was no effect of the administration of the goitrogen, propylthiouracil (10 micrograms/day im), on the E2 induced development of the shell gland.