Growth rates of male and female equine embryos between Days 6 and 15 of pregnancy

Abstract

Summary To see whether any indication could be found that male conceptuses might develop more rapidly than females in the horse, as they do in several other mammals, pre‐attachment growth rates of female and male conceptuses were estimated from composite curves derived from the diameters of 36 female and 39 male conceptuses each measured once when collected at known times between six and 15 days after ovulation. The conceptuses were sexed cytogenically during the course of a previously reported study. The overall rates of growth (increase in conceptus diameter) were not significantly different for males and females. However, on any given day there was great variation in size amongst embryos and much overlap between the sizes of males and females. It is concluded that comparison of the growth rates of individual embryos, obtained by repeated echographic measurements, might reduce this variability and be a more useful means of continuing this investigation.

Uterine influences on embryogenesis and early placentation in the horse revealed by transfer of day 10 embryos to day 3 recipient mares

“…In normal pregnancy, once the embryo enters the uterus on day 6, its growth is exponential from day 6 until approximately day 15 (Ginther 1983a, Leith & Ginther 1984. Ultrasonographically, the embryonic vesicle can be seen to expand rapidly between days 11 and 15 of gestation (Ginther et al 1985, Ginther 1986, Romagnano et al 1989) after which expansion slows and then plateaus at around day 18. The delayed rapid expansion phase noted in the Figure 2 The mean (GS.E.M.)…”

The effects of an advanced uterine environment on embryonic survival in the mare

“…Note how the transferred embryos are retarded in diameter for their age, and that 3 of them were no longer visible when they were aged 18 days. Mean embryonic vesicle sizes reported for 75 individual conceptuses (᭹) by Romagnano et al[74] and from 9 embryos measured at 2 day intervals ( ) by Wilsher and Allen[12] are depicted for comparison. (a) Unicornuate asynchronous twins created by transfer of a Day 8 embryo to a Day 11 pregnant mare.…”

Post fetal death development of endometrial cups in a Jenny donkey (Equus asinus)

“…The timings of these important developmental events have not been studied previously in the horse-in-donkey and donkey-in-horse extraspecies models, and in the present horse-in-donkey pregnancy, the embryonic vesicle, when first scanned, had a diameter consistent with its own age (Romagnano et al 1989) rather than that of the uterus which was 2 days behind. Thereafter, however, it slowed its developmental rate to that of the uterus, as has been reported previously in horse-in-horse embryo transfers ( and Allen, 2009;Wilsher et al 2010;Gibson et al 2017).…”