Xuezhong Qin

Date of Graduation

1992

Document Type

Dissertation/Thesis

Abstract

The Ca supply for eggshell formation depends on the rate of calcium transport in both the intestine and shell gland. Although estrogen (E{dollar}\\sb2){dollar} is known to play an important role in the regulation of Ca transport in these tissues, the mechanism responsible for this effect has not been elucidated. Study 1, 2, and 3 were thus conducted to determine the role of E{dollar}\\sb2{dollar} in the regulation of Ca-ATPase and alkaline phosphatase (AP) in both the shell gland and intestine of immature chicks. In the shell gland, E{dollar}\\sb2{dollar} treatment increased the Vmax of Ca-ATPase without increasing the affinity of Ca-ATPase for Ca. This stimulating effect was not modified by D{dollar}\\sb3.{dollar} AP activity in the shell gland, however, was not significantly increased by either E{dollar}\\sb2{dollar} or D{dollar}\\sb3.{dollar} In the intestine, E{dollar}\\sb2{dollar} treatment significantly increased AP activity. Ca-ATPase activity was increased by D{dollar}\\sb3,{dollar} but not E{dollar}\\sb2{dollar} or Ca deficiency. The positive effect of E{dollar}\\sb2{dollar} on AP was only observed in D{dollar}\\sb3{dollar}-replete chicks and restricted to the intestine only. Boron (B) has been reported to increase plasma E{dollar}\\sb2{dollar} concentrations and Ca retention in mammals and young chicks. Study 4 was thus conducted to determine the effect of dietary B on eggshell thickness and plasma E{dollar}\\sb2{dollar} concentrations in aging broiler breeder hens. B at 60 to 100 ppm failed to increase shell thickness, Ca retention or concentrations of E{dollar}\\sb2{dollar} and Ca in the plasma although it increased tibial bone ash. In Study 5, the effect of E{dollar}\\sb2{dollar} pellets on egg production and shell quality was determined in molted hens. E{dollar}\\sb2{dollar} treatment increased plasma Ca concentrations and tibial bone ash but was without positive effect on egg production and shell quality. Ca-ATPase and AP in the shell gland and intestine are thus differentially regulated by E{dollar}\\sb2.{dollar} E{dollar}\\sb2{dollar} may increase Ca transport in the shell gland by stimulating Ca-ATPase and in the intestine by stimulating AP. In the laying hen, counter-regulatory mechanism are suggested to limit the E{dollar}\\sb2{dollar}-induced effect on shell gland Ca transport.

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