Characteristics of peaks in serum concentrations of follicle-stimulating hormone and estradiol, and follicular wave dynamics during the interovulatory interval in cyclic ewes

Toosi, B.M.; Seekallu, S.V.; Barrett, D.M.W.; Davies, K.L.; Duggavathi, R.; Bagu, E.T.; Rawlings, N.C.

doi:10.1016/j.theriogenology.2009.11.005

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Volume 73, Issue 9 , Pages 1192-1201, June 2010

Characteristics of peaks in serum concentrations of follicle-stimulating hormone and estradiol, and follicular wave dynamics during the interovulatory interval in cyclic ewes

B.M. Toosi
S.V. Seekallu
D.M.W. Barrett
- Present address: Department of Plant and Animal Sciences, Nova Scotia Agriculture College, Bible Hill, Nova Scotia, B2N 5E3, Canada.
K.L. Davies
- Present address: Department of Animal and Poultry Science, College of Agriculture and Bioresources, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5A8, Canada.
R. Duggavathi
- Present address: Department of Animal Sciences, McGill University Macdonald Campus, 21111 Lakeshore Road Ste. Anne de Bellevue, Quebec, H9X 3V9, Canada.
E.T. Bagu
- Present address: Centre de Recherche-CHUM Hospital Notre-Dame, Y-5625-2099 Rue Alexandre de Séve, Montreal, Quebec, H2L 2W5, Canada.
N.C. Rawlings
- Corresponding author. Tel.: +1 306 966 7373/1324; fax: +1 306 966 7376.

Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Received 12 June 2009; received in revised form 3 November 2009; accepted 4 November 2009. published online 29 March 2010.

Abstract

There are three or four ovarian follicular waves in the interovulatory interval of cyclic ewes. Each follicular wave is preceded by a transient peak in serum follicle-stimulating hormone (FSH) concentrations. Serum concentrations of estradiol also increase concurrent with the growth of follicle(s) in each wave. In the current study, we investigated the patterns of follicular wave development and characteristics of FSH and estradiol peaks in all follicular waves of the interovulatory interval and after induction of a supraphysiologic FSH peak in cyclic ewes (Ovis aris). In Experiment 1, 19 ewes underwent daily ovarian ultrasonography and blood sampling for a complete interovulatory interval. In Experiment 2, seven ewes received two administrations of ovine FSH (oFSH), 8h apart (1μg/kg; sc), at the expected time of the endogenous FSH peak preceding the second follicular wave of the interovulatory interval. In Experiment 1, the amplitude of the FSH peaks decreased (up to 50%), whereas basal serum FSH concentrations increased across the interovulatory interval (P<0.05). Maximum follicular diameter was greater (P<0.05) for Wave 1 and the Ovulatory wave (6.0±0.3 and 6.1±0.2mm, respectively) than for Waves 2 and 3 (5.3±0.1 and 5.4±0.3mm, respectively). Life span was greater for follicles in Wave 1 compared with other waves (P<0.05). Treatment with oFSH increased the amplitude of an FSH peak by 5- to 6-fold. This treatment increased estradiol production (P<0.05) but had little effect on other characteristics of the subsequent follicular wave. We concluded that changes in the amplitude and duration of the peaks in serum concentrations of FSH that precede follicular waves across the interovulatory interval do not influence the characteristics of the follicular waves that follow.