Abstract

BackgroundCracked shells, due to age related reduction of shell quality, are a costly problem for the industry. Parallel to reduced shell quality the skeleton becomes brittle resulting in bone fractures. Calcium, a main prerequisite for both eggshell and bone, is regulated by estrogen in a complex manner. The effects of estrogen, given in a low continuous dose, were studied regarding factors involved in age related changes in shell quality and bone strength of laying hens. A pellet containing 0.385 mg estradiol 3-benzoate (21-day-release) or placebo was inserted subcutaneously in 20 birds each of Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) at 70 weeks of age. Eggs were collected before and during the experiment for shell quality measurements. Blood samples for analysis of total calcium were taken three days after the insertion and at sacrifice (72 weeks). Right femur was used for bone strength measurements and tissue samples from duodenum and shell gland were processed for morphology, immunohistochemical localization of estrogen receptors (ERα, ERβ), plasma membrane calcium ATPase (PMCA) and histochemical localization of carbonic anhydrase (CA).ResultsEstrogen treatment increased shell thickness of both hybrids. In addition, shell weight and shell deformation improved in eggs from the brown hybrids. The more pronounced effect on eggs from the brown hybrid may be due to a change in sensitivity to estrogen, especially in surface epithelial cells of the shell gland, shown as an altered ratio between ERα and ERβ. A regulatory effect of estrogen on CA activity, but not PMCA, was seen in both duodenum and shell gland, and a possible connection to shell quality is discussed. Bone strength was unaffected by treatment, but femur was stronger in LSL birds suggesting that the hybrids differ in calcium allocation between shell and bone at the end of the laying period. Plasma calcium concentrations and egg production were unaffected.ConclusionsA low continuous dose of estrogen improves shell strength but not bone strength in laying hens at the end of the laying period.

Highlights

  • IntroductionDue to age related reduction of shell quality, are a costly problem for the industry

  • Cracked shells, due to age related reduction of shell quality, are a costly problem for the industry

  • We have shown that both estrogen receptors (ERα and ERβ) are present in the functional shell gland of laying hens [7] and preliminary data from our group show that a shift in the balance between these receptors coincides with reduced shell quality

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Summary

Introduction

Due to age related reduction of shell quality, are a costly problem for the industry. The effects of estrogen, given in a low continuous dose, were studied regarding factors involved in age related changes in shell quality and bone strength of laying hens. Right femur was used for bone strength measurements and tissue samples from duodenum and shell gland were processed for morphology, immunohistochemical localization of estrogen receptors (ERα, ERβ), plasma membrane calcium ATPase (PMCA) and histochemical localization of carbonic anhydrase (CA). Age related reduction in shell quality is a costly problem for the table egg industry. Carbonic anhydrases (CA) have been implicated in shell formation for nearly 70 years [3], when Benesch and co-workers demonstrated that inhibition of CA in laying hens results in soft-shelled or shell-less eggs. Evidence exists suggesting that regulation of CA by estrogen may take place in the laying hen shell gland

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