Follicular kinetics in the mare ovary

Abstract

Summary. Using histological techniques, 8 ovaries (1 per mare) of riding or pony mares were studied at different physiological states : 2 ovaries were collected during anoestrus, 4 during early pregnancy, 2 before (day 33) and 2 after (day 43) the onset of PMSG secretion, and 2 during the oestrous season. On each ovary all the follicles greater than 50 y (one complete layer of round follicle cells) were counted, measured, checked for atresia and calculated for mitotic index. The mean total number of follicles larger than 50 fL in diameter was 48 ! 27 per mare, 23 j; 11 of which were antral (> 300 in diameter).Atresia was rarely seen in follicles < 350 !. in diameter, and the mean number of atretic follicles was 14 ! 10 per mare. Thus, the follicular population in the mare was numerically much smaller than in the ewe or the cow. To study the follicular population at different physiological states, the follicles were pooled and divided into four groups : preantral (< 300 fL in diameter), small-antral (< 1 500 !,), large-antral (< 10 000 !) and preovulatory (> 10 000 p.). The first three size groups from ovaries collected during the ancestrous or oestrous season showed no difference in the mean number of follicles, incidence of atresia or mitotic index. The fourth group of follicles was different as there were no preovulatory follicles in anoestrous mares. The ovaries of pregnant mares submitted to PMSG for 6 days contained significantly more follicles in the small-antrum group than the control ovaries (day 33 of pregnancy). PMSG also seemed to modify antrum formation. In contrast, PMSG seemed to have no effect on follicle number or atresia in the large-follicle population. Follicular growth rates were estimated by two methods : -follicles larger than 5 000 in diameter : cauterization of the preovulatory follicles during late oestrus showed that a follicle of less than 5 000 needed about a week to grow to ovulatory size ; -follicles between 60 and 1 000 fL in diameter : measurement of the mitotic index indicated a follicle needed about 7 weeks to enlarge from 60 to 1 000 y. Thus, follicular growth in the mare seemed to be much faster than in the ewe.Introduction.

Mathematical modelling of oxygen transport-limited follicle growth

“…The comparison of these predictions with the data for human follicles shows that real follicle growth is consistent with the pattern expected, if antrum formation and subsequent volume increase are mechanisms for overcoming oxygen transport limitations. This pattern of growth is consistent with that observed in other mammals (Turnbull et al 1977, Driancourt 1979. It should be noted that Fig.…”

An autoradiographic study of follicle growth in the ovaries of cyclic rats

“…Total time of follicle development also varies between species. In the ewe and in the mare (Driancourt 1979) it is much longer than in mice, hamsters and rats in which it is about 3 weeks (Pedersen 1972;Chiras & Greenwald 1977;pre¬ sent study). For the rat we arrive at a total time of development from types 3b to ovulation of 23 days, if we include, on the basis of data of Welschen (1973) and Hirshfield & Midgley (1978), 4 days for the transit time through the types 7 and 8 which was not determined in the present study.…”

Follicular fluid leptin concentrations and expression of leptin and leptin receptor in the equine ovary and in vitro-matured oocyte with reference to pubertal development and breeds

“…In our study, it is possible that serum and follicular concentrations of Ob were the same in draft and Standardbred mares because Standardbred mares were submitted to a fattening period of 40 days before slaughter but we are unable to comment on the serum levels of Ob in the Standardbred mares before the fattening period. This period, however, would probably not have been sufficient to improve the efficiency of in vitro maturation in these animals used to an intensely competitive life, because ovogenesis requires a period of 60 days (Driancourt 1979). So, it appears that in these mares, Ob concentration in follicular fluid only partially influences oocyte maturation in vitro.…”