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Follicular waves are associated with transient fluctuations in FSH but not oestradiol or inhibin-A concentrations in anoestrous ewes

Published online by Cambridge University Press:  18 August 2016

A.C.O. Evans ,
P. Duffy ,
K. M. Quinn ,
P. G. Knight  and
M. P. Boland
A.C.O. Evans
Affiliation:
Department of Animal Science and Production, University College Dublin, Dublin 4, Ireland
P. Duffy
Affiliation:
Lyons Research Farm, Conway Institute for Biomolecular and Biomedical Research, University College Dublin, Dublin 4, Ireland
K. M. Quinn
Affiliation:
Department of Animal Science and Production, University College Dublin, Dublin 4, Ireland
P. G. Knight
Affiliation:
School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading, UK
M. P. Boland
Affiliation:
Department of Animal Science and Production, University College Dublin, Dublin 4, Ireland
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Abstract

The aim was to examine statistically the changes among days in the numbers of follicles relative to the growth of large follicles to test the hypothesis that follicular development occurs in a wave-like fashion in anoestrous ewes. The relationships among the patterns of circulating concentrations of FSH, oestradiol and inhibin-A and the pattern of follicular growth as well as relationships among follicular fluid steroid and inhibin-A concentrations were also studied. The ovaries of 11 ewes were examined daily using transrectal ultrasonography for 14 days and blood samples were collected every 8 h for 9 days. Five ewes were ovariectomized on the last day of ultrasound scanning. One to three identified follicles (a cohort) emerged every 2 to 5 days (mean 2·9 (s.e. 0·2) days) in individual ewes. The numbers of 4 and 5 mm follicles were fewest (P < 0·05) before and greatest (P < 0·05) 1 day after cohort emergence. This change in the numbers of follicles indicates a wave-like pattern of follicular growth. FSH concentrations were greatest (P < 0·05) on the day before wave emergence and lowest (P < 0·05) on the day of wave emergence. Peripheral concentrations of oestradiol and inhibin-A did not fluctuate (P > 0·05) in association with the emergence of follicular waves. The follicles that were collected at ovariectomy originated from one of three different waves. Oestradiol and inhibin-A concentrations in follicular fluid and the oestradiol-to-progesterone ratio were not different among the largest follicles of successive waves, when follicles were collected at the same time, indicating that new waves of follicles developed before the demise of old waves.

In conclusion, waves of follicles emerged about every 3 days in anoestrous ewes (defined as significant changes in numbers of follicles) and were associated with fluctuations in FSH concentrations but not peripheral oestradiol or inhibin-A concentrations. New follicular waves also emerged in the presence of steroidogenically active (positive oestradiol-to-progesterone ratio), inhibin-A producing follicles from a previous wave suggesting that follicles do not exert functional dominance during the non-breeding season.

Keywords

folliclesFSHinhibinoestradiolsheep
Type
Reproduction
Information
Animal Science , Volume 72 , Issue 3 , June 2001 , pp. 547 - 554
Copyright
Copyright © British Society of Animal Science 2001

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