Miniature ponies: 2. Endocrinology of the oestrous cycle
O. J. Ginther A B , M. A. Beg B , A. P. Neves C , R. C. Mattos C , B. P. L. Petrucci C , M. O. Gastal A and E. L. Gastal B DA Eutheria Foundation, Cross Plains, WI 53528, USA.
B Department of Pathobiological Sciences, University of Wisconsin, Madison, WI 53706, USA.
C Department of Animal Medicine, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil.
D Corresponding author. Email: egastal@svm.vetmed.wisc.edu
Reproduction, Fertility and Development 20(3) 386-390 https://doi.org/10.1071/RD07165
Submitted: 17 September 2007 Accepted: 11 December 2007 Published: 8 February 2008
Abstract
Plasma concentrations of FSH, LH, oestradiol and progesterone were studied daily during 12 interovulatory intervals and 21 periovulatory periods in nine Miniature ponies. The peak of the FSH surge that was temporally associated with emergence of the future ovulatory follicle occurred when the follicle was ~9 mm, compared with a reported diameter of 13 mm in larger breeds. The ovulatory LH surge involved a slow increase between Days 13 and 18 (ovulation = Day 0; 0.6 ± 0.1 ng day–1), a minimal increase or a plateau on Days 18 to 21 (0.04 ± 0.1 ng day–1), and a rapid increase after Day 21 (2.2 ± 0.4 ng day–1; P < 0.0001). The end of the plateau and the beginning of the rapid increase occurred on the day of maximum concentration in the oestradiol preovulatory surge. An unexpected mean increase and decrease in LH occurred (P < 0.04) on Days 5 to 9. Concentrations of oestradiol and progesterone seemed similar to reported results in larger breeds. Results indicated that in Miniature ponies the peak of the FSH surge associated with emergence of the future ovulatory follicle occurred at a smaller diameter of the future ovulatory follicle than in larger breeds, the ovulatory LH surge increased in three phases, and the ovulatory LH surge was followed by an LH increase and decrease during the early luteal phase.
Additional keywords: gonadotropins, Miniature pony mares, ovarian steroids, ovaries.
Acknowledgements
This research (Project MP1-APN-04) was supported by the Federal University of Rio Grande do Sul (Porto Alegre, RS, Brazil), PRONEX CNPq/FAPERGS, and the Eutheria Foundation, Inc., Cross Plains, Wisconsin, USA. The authors thank Mr. Santo Sérgio Feoli, Cabanha Morada das Pôneis, for use of the mares; Alisul Alimentos S. A., Brazil for a gift of the commercial ration; Dee Cooper for assistance with the figures and statistical analyses; and A. F. Parlow of the National Hormone and Peptide Program (NHPP) for eFSH and eLH. R. C. Mattos thanks the CNPq for a Research Fellowship. The authors declare that there is no conflict of interest that would prejudice the impartiality of this scientific work.
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