Mechanisms of estrogen-induced effects in avian reproduction caused by transovarian application of a xenoestrogen, diethylstilbestrol

Abstract

To clarify breeding failure in avian species caused by the estrogenicity of chemicals, alterations in the reproductive systems of Japanese quail exposed in ovo to a xenoestrogen were investigated. An injection of diethylstilbestrol (DES) into the yolk before incubation decreased, after sexual maturation, egg-laying performance of female quails, which accompanied inducing abnormal development of the oviducts. All females treated with 50 ng DES/g of egg did not lay eggs, while 0.5-5 ng DES/g reduced egg weight and eggshell strength and thickness. In the uterus (shell gland), the mRNAs for calcium regulating factors, osteopontin and calbindin D28 K, were reduced dose-dependently by DES. Scanning electron microscopy showed that shell thinning was pronounced in the mammillary and cuticular layers of the eggshell, regions where osteopontin proteins are reportedly located. These indicate that transovarian exposure to xenoestrogens causes malformation and dysfunction of the oviducts, where calcium regulating molecules could play key roles in eggshell thinning.

Evaluation of the impact of in‐ovo exposure to dicofol on avian reproduction

“…A reduction in transcript levels of the CYP11A1 gene in the gonads of male chicks, consistent with our results from in ovo exposure to estrogen analogs [6,21,22], further indicated the estrogenic potency of o,p 0 -dicofol in living organisms. Reduction in concentration of the cholesterol side-chain cleavage enzyme may cause depletion of the precursors of steroid hormones during development, although concentrations of mRNAs for the other enzymes were not markedly altered.…”

“…Therefore, the impacts of estrogenic compounds on living birds cannot be estimated only from their potential to activate the ER in vitro. We previously reported that the effects on the genital tracts of Japanese quails of in ovo DES treatment prior to incubation markedly differ from treatment at 10 d of incubation [19,21]. Early exposure to DES caused greater disruption to the elongation of both the left and right genital tracts than did later exposure and stunted egg-laying itself, but late exposure caused greater impairment to eggshell formation without greatly damaging egg production.…”

“…Samples of the gonad were removed for analysis of gene expression and kept at À808C until analysis. Quails were fed on commercial diets (PLD-CHICK for chicks and PLD from five weeks of age, Oriental Yeast Company) and kept under optimal air conditions [6,21]. They were divided according to sex 10 d after hatching.…”

“…Quails were reared according to our protocol [6,21]. Briefly, eggs were moved to hatching boxes on day 15 of incubation and hatched chicks were collected on days 17 and 18, each tagged with a leg band and moved to brooders in mixed sex groups for each treatment.…”

Dietary calcium deficiency in laying ducks impairs eggshell quality by suppressing the process of shell biomineralization

“…For example, injecting pellets of estradiol 3-benzoate subcutaneously in laying hens was reported to increase shell thickness and improve shell deformation (Wistedt et al, 2014). In contrast, an injection of 0.5-5 ng g −1 diethylstilbestrol (DES) into the yolk before incubation decreased later egg weight, shell strength and thickness, which accompanied abnormal development of the oviducts after sexual maturation (Kamata et al, 2009). To date, whether the effect of calcium on shell quality is mediated by estradiol remains unclear despite a potential role of estradiol either in mediating calcium metabolism (Bar et al, 1996) or in regulating the key enzyme involved in the process of shell calcification (Bar et al, 1996;Holm et al, 2001;Berg et al, 2004;Kamata et al, 2009).…”