Multiple Rinses of Eggshells for Recovery of Aerobes

s of papers 55 230 Role of estrogen in avian osteoporosis. M. M. Beck*1 and K. K. Hansen2, 1University of Nebraska-Lincoln, Lincoln, NE, 2University of Nebraska Medical Center, Omaha, NE. One of the difficulties associated with commercial layer production is the development of osteoporosis in hens late in the production cycle. In light of this fact and because of the hen’s unique requirement for calcium (Ca), many studies have focused on the regulation of Ca and the role(s) of estrogen (E2) in this process. The time course of E2 synthesis over the productive life of the hen has been well documented; increased circulating E2 accompanies the onset of sexual maturity while decreases signal the declines in egg production prior to a molt. E2 receptor populations decrease with age in numerous tissues; the parallel changes in calcium-regulating proteins, primarily Calbindin D28k, and in the ability of duodenal cells to transport Ca, are thought to occur as a result of the changes in estrogen, and are also reversible by the molt process. In addition to the traditional model of E2 action, evidence now exists for a possible ”non-genomic” action of E2 via membrane-bound receptors, demonstrated by extremely rapid surges of ionized Ca in chicken granulosa cells in response to 17b-E2. E2 receptors have also been discovered in duodenal tissue; and tamoxifen, which is known to bind to the estrogen receptor, has been shown to cause a rapid increase in calcium transport in duodenum. In addition, recent evidence also suggests that mineralization of bone per se may not explain entirely the etiology of osteoporosis in the hen but that changes in the collagen matrix may contribute through decreases in bone elasticity. Taken together, these studies suggest that changes in E2 synthesis and E2 receptor populations may underlie the age-related changes in bone; as with postmenopausal women, dietary Ca and/or Vitamin D are of limited benefit as remedies for osteoporosis in the hen.