![]() We investigated whether there were differences in estradiol -17ß concentrations between lines at different ages that could be related to selection for high egg production or phylogenetic origin of the animals, and whether there was an influence of housing conditions on estradiol-17ß. The high performing white egg (WLA) and brown egg (BLA) layer lines as well as the low performing white (R11) and brown (L68) layer lines were kept in both single cages and a floor housing system. In this study we analyzed estradiol-17ß concentration in laying hens of four pure bred chicken laying lines at four different time intervals of the laying period (17th–19th week of age, 33rd–35th week of age, 49th–51st week of age, and 72nd week of age). The estrogen estradiol-17ß is known as one of the major gonadal steroid hormones with different functions in reproduction. As with postmenopausal women, dietary Ca and vitamin D are of limited benefit as remedies for osteoporosis in the hen. Taken together, these studies suggest that changes in estrogen synthesis and estrogen receptor populations may underlie the age-related changes in avian bone. ![]() 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. Estrogen receptors have also been discovered in duodenal tissue, and tamoxifen, which binds to the estrogen receptor, has been shown to cause a rapid increase in Ca transport in the duodenum. In addition to the traditional model of estrogen action, evidence now exists for a possible nongenomic action of estrogen via membrane-bound receptors, demonstrated by extremely rapid surges of ionized Ca in chicken granulosa cells in response to 17beta-estradiol. 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. Numbers of estrogen receptors decrease with age in numerous tissues. The time course of estrogen synthesis over the productive life of hens has been well documented increased circulating estrogen accompanies the onset of sexual maturity while decreases signal a decline in egg production prior to a molt. In light of this fact and because of hens' unique requirements for Ca, many studies have focused on the regulation of Ca and the role of estrogen in this process. One of the difficulties associated with commercial layer production is the development of osteoporosis in hens late in the production cycle.
0 Comments
Leave a Reply. |