Role of estrogen in avian osteoporosis

Abstract

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 hens' unique requirements for Ca, many studies have focused on the regulation of Ca and the role of estrogen in this process. 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. Numbers of estrogen receptors 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 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. 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, 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 estrogen synthesis and estrogen receptor populations may underlie the age-related changes in avian bone. As with postmenopausal women, dietary Ca and vitamin D are of limited benefit as remedies for osteoporosis in the hen.

Novel Nonsurgical Approach to Stabilization of Bilateral Pathologic Femoral Fractures in an Egg-laying Maroon-bellied Conure (Pyrrhura frontalis)

“…4,5 Factors contributing to decreased bone integrity include inactivity, reproductive activity, bedding substrate, enclosure type and size, population density, dietary inadequacies (eg, phosphorus, vitamin D 3 , and magnesium deficiencies), lighting spectrum and intensity, photoperiods, genetics, and bony neoplasms. 2,4,[6][7][8][9][10][11][12][13][14][15][16][17] Because both internal and external fixation involve placing hardware in bone, external coaptation may be the only option other than euthanasia for pathologic fractures.…”

“…7,8,25 In chickens, producing a single eggshell may require up to 10%-15% of the total body calcium stores. 26 Hens increase their caloric intake by 25% during egg laying to maximize intestinal sources of calcium; however, only 60%-75% of eggshell calcium is derived from the diet, with the remaining 25%-40% coming from bone and other calcium stores.…”

Bioelectric Activity of Interneurones of Spinal Cord in the Experimental Menopause in Femal Rats

“…Також зростання амплітуди N-компо-нентів може бути пов'язане зі зрушенням потенціалу залежності активації натрієвих каналів так, що для досягнення порога і генерації натрієвого струму нормального значення потрібні менші рівні деполяризації [20]. Спричинити це може зниження вмісту кальцію у крові та міжклітинній рідині, зу-мовлене дефіцитом естрогенів [21].…”

Interrelationships of body weight and bone weight with densitometric properties of tibiotarsal bone in geese during post-hatching development

“…Studies on peripheral skeletal system properties in growing meat-type poultry species have shown that body weight gain is associated with decreases in the amount of bone tissue as well as changes in densitometric properties (Charuta and Cooper 2012;Charuta et al 2012a;Charuta et al 2012b;Charuta et al 2012c;Charuta 2013;Charuta et al 2013a;Charuta et al 2013b). The observed developmental changes in long bones were found to be correlated both with the age and sex of birds (Beck and Hansen 2004).…”