Luteogenic and luteotropic effects of eCG during pregnancy in the mare

eCG concentrations, luteal structures, return to cyclicity, and postabortion fertility in embryo transfer recipient mares

“…Only the primary CL, which originated from the ovulation(s) before embryo transfer, was detected. This finding contrasts with other studies in which all mares were found to have at least one supplementary CL during pregnancy [25]. Considering that the mares were only available for study from 60 to 75 days of gestation, it is possible that one or more supplementary CL could have developed at a later stage.…”

“…Several mares with no supplementary CL had relatively high concentrations of eCG at the time of the scan (median, 20 IU/mL). Therefore, the absence of supplementary CL in these mares was not explained by the low eCG concentration as it has been proposed [25]. It is worth noting, however, that the majority of these mares (60%) were transferred early in the breeding season (September).…”

Review of the reproductive endocrinology of the pregnant and parturient mare

“…Equine chorionic gonadotropin is secreted by the endometrial cups, explants of binucleate trophoblast that detach from the chorionic girdle of the conceptus and colonize the endometrium. Secretion begins in the sixth week of equine pregnancies long after maternal recognition of pregnancy has occurred (prevention of programmed luteolysis), providing direct luteotrophic support [79,80] but at a much later stage of pregnancy than does the CG of primates. Primate CG is secreted at the late blastocyst stage within a day or two of endometrial attachment, preventing programmed luteal regression that otherwise maintains nonpregnant females in a cyclic state [81,82], the primate maternal recognition of pregnancy in other words.…”

“…Secretion of eCG is extremely variable among mares and is influenced by a variety of factors [74] including nutrition [86], uterine environment [87], and genetics [88], but it is highly correlated with maternal progesterone concentrations and numbers of accessory corpora lutea between weeks 5 and 20 of gestation [47,62,79]. The decline in luteal tissue weight, that begins as early as GD 60 [62], occurs in concert with regression of the endometrial cups, decreasing eCG concentrations [89] and with concomitant development of the allantochorion [90].…”

Effect of month of conception on fertility of mares inseminated with jackass semen

“…Trying to assess the role of eCG in pregnant mares inseminated with stallions or jackasses, Boeta and Zarco (2012) compared the primary and supplementary corpora lutea, in both groups, as well as the concentrations of eCG and progesterone. No differences were found in progesterone or eCG concentrations between mares with mule pregnancies that accumulated different numbers of supplementary corpora lutea.…”