Fertility decline in aging roosters is related to increased testicular and plasma levels of estradiol

Simy Weil*, Israel Rozenboim, A. Allan Degen, Alistair Dawson, Michael Friedländer, Avi Rosenstrauch

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


The relationships between testicular and plasma hormone levels and the decline in fertility in aging roosters were examined. Body mass, testicular mass, and fertility were measured in roosters from 20 to 72 weeks of age. Plasma was assayed for LH and testosterone, and estradiol and testicular extracts were assayed for testosterone and estradiol contents. Fertility increased rapidly in young roosters to a peak of 96.2 ± 3.9% at 37 weeks of age. Thereafter, fertility declined and by 72 weeks of age was significantly lower than at 37 weeks. Plasma LH reached 16.8 ± 2.5 ng/ml at 27 weeks and remained high until 60 weeks of age, when it decreased significantly. Plasma and testicular testosterone levels increased from low levels in young birds to a peak that coincided with highest fertility and declined thereafter. Plasma and testicular estradiol showed a striking inverse relationship with testosterone. Plasma estradiol was 29.4 ± 4.0 pg/ml in 20-week-old birds, decreased rapidly as testosterone increased, and increased again in older birds as testosterone decreased. Thus, the decline in fertility in aging roosters was associated with a decrease in plasma LH and testosterone and an increase in plasma and testicular estradiol. It is suggested that plasma levels of LH and testosterone in roosters are regulated by a negative feedback mechanism involving estradiol that is produced not only by the aromatization of testosterone in the brain but also by peripheral estradiol originating in the testes and that estradiol has a major role in the decline in fertility in aging roosters.

Original languageAmerican English
Pages (from-to)23-28
Number of pages6
JournalGeneral and Comparative Endocrinology
Issue number1
StatePublished - Jul 1999

Bibliographical note

Funding Information:
We thank David Galili and Mario Taliansky from Kibbutz Shuval for providing the roosters, Abdullah Abou-Rachbah for taking care of the animals, and three anonymous reviewers for providing very useful suggestions. This study was partially supported by a grant from the Israel Ministry of Agriculture.


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