Older hens in production lay larger but fewer eggs than younger birds, and the incidence of soft and broken shells is greater in older hens than younger. These changes are attributable at least in part to changing hormone profiles and diminished ability of the hen to transport calcium at the duodenum. In further exploration of this relationship, a study was conducted with three ages of Hy-Line W-36 birds: prelay pullets (PL; 19 wk, 0% production), peak-production hens (PP; 29 wk, ∼93% production), and late-stage hens (LS; 71 wk, ∼80% production). Hens from the PP and LS groups were palpated for presence of an egg in the shell gland; hens were then euthanized and tissues (kidney, shell gland, hypothalamus) were removed for quantification of estrogen receptor- α (ERα) populations via immunocytochemical and Western blot analyses. Localization of ERα by immunostaining in the shell gland showed differences among age groups; however, no differences were noted in localization of ERα between age groups in the kidney and hypothalamus. In both the kidney and the shell gland there was a decrease in the amount of ERα, as detected by immunoblotting, in the LS hens compared to PL and PP birds (P \u3c 0.05). The results suggest that failure of calcium regulating mechanisms with age may be mediated at least in part through the reduced populations of estrogen receptors in certain critical tissues
