Follicle diameters and hormone concentrations in the development of single versus double ovulations in mares.
Relationships between double ovulations and plasma hormone concentrations were compared between 18 single ovulating and 6 double ovulating mares. The study began when the first follicle reached >or=30 mm, and ultrasound scanning and blood sampling were done every 12h to Day 3 (ovulation=Day 0). Data were analyzed for 2.5 d after the largest follicle was >or=30 mm and after Day -2.5 to encompass the mean 5-d interval between a >or=30 mm follicle and Day 0. During the 2.5 d after >or=30 mm, the increasing diameter of the largest follicle was less pronounced and plasma FSH concentrations were lower (approached significance) in the double ovulators than in the single ovulators. By Day -2.5, the largest follicle was smaller (P<0.01) and plasma FSH was lower (P<0.04) in the double ovulators. Plasma estradiol concentrations were higher (P<0.001) during the 2.5 d after >or=30 mm in the double ovulators and the correlation between estradiol and FSH was negative (r=-0.39, P<0.0001). In double ovulators, compared to single ovulators, the largest follicle was smaller, FSH was lower and estradiol was higher on most occasions between Days -2.5 and -0.5 (P<0.05), but plasma concentrations of LH and ir-inhibin were not significantly different. In conclusion, smaller preovulatory follicles in double ovulators were a response to lower FSH concentrations, due to higher estradiol concentrations from two preovulatory follicles; preovulatory differences in hormone concentrations between single and double ovulators were an effect rather than a cause of the double ovulations.
Ginther
O J
OJ
Eutheria Foundation, Cross Plains, WI 53528, USA. ginther@svm.vetmed.wisc.edu
Gastal
E L
EL
Rodrigues
B L
BL
Gastal
M O
MO
Beg
M A
MA
D000818:Animals; D004958:Estradiol / Q000097:blood*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood*; D006736:Horses / Q000097:blood / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood*; D006080:Ovarian Follicle / Q000502:physiology*; D010060:Ovulation / Q000502:physiology*; D018709:Statistics, Nonparametric
D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone