Luteal vascularity and embryo dynamics in mares during early gestation: Effect of age and endometrial degeneration

Abstract

Contents The present study characterized the luteal status and the dynamic of the conceptus during the first 20 days of gestation in mares with different ages and degrees of endometrial degeneration. Total area of the corpus luteum (CL), luteal vascularity, CL area with blood signals, progesterone concentrations (P4), embryonic vesicle diameter, number of embryonic location changes, embryonic fixation position and uterine contractility were evaluated. In Experiment 1, mares ≤6 years of age (Young group, 5.6 ± 0.2 years, n = 7 mares) and mares ≥15 years of age (Old group, 17.2 ± 0.9 years, n = 6 mares) were used to investigate the effect of age. In Experiment 2, the luteal and embryonic parameters were compared between mares with minimal (Mild group, endometrial category I, n = 9 mares) and severe (Severe group, endometrial category III, n = 7 mares) endometrial degeneration. The Old and Severe groups had greater (p ≤ 0.04) total CL area and reduced luteal vascularity (p ≤ 0.04) than the Young and Mild groups, respectively. However, P4 levels and CL area with blood signals were similar (p ≥ 0.8) between the groups. A negative effect of age (p < 0.01), but not of endometrial degeneration (p = 0.6), was found for the embryonic vesicle diameter. The conceptus mobility was high (p > 0.1) until day 14 of gestation in the Severe group, while a reduced number of changes of the embryo location was detected earlier (p < 0.05) in the Old group. In conclusion, the newly formed CL of aged mares and mares with severe endometrial degeneration suffered a structural remodelling to safeguard the local blood supply and the continuous P4 output during early gestation. Moreover, an earlier reduction of the embryonic mobility and a delayed development of the conceptus were associated with advanced age, regardless of the degree of endometrial degeneration.

Maternal age affects equine Day 8 embryo gene expression both in trophoblast and inner cell mass

“…Their inhibition is detrimental for embryo development 87 . Thus, both reduced ATP production and disturbed ion channels’ function may impact embryo growth, although effects of mares’ age on embryo growth are controversial 24–28 .…”

Spectral Doppler ultrasound in selecting an equine embryo receiver

“…Disagreeing with Lemos et al (2018), age was not a factor that influenced none of the indices that evaluated in the study. As demonstrated by Ferreira et al (2019), the newly formed CL in old mares undergoes compensatory structural remodelling to ensure local blood supply and continuous P4, which maintain during early pregnancy without being influenced by the age effect. Also, we believe that age has not influenced these mares either, due to the use of balanced feed that meets the needs of embryo-receiving mares and the fact that the mares included in elderly mare group is not in the extreme within the category, not presenting worthy circulatory changes that would cause greater problems pregnancy within the normal range.…”

Maternal age affects equine day 8 embryo gene expression both in trophoblast and inner cell mass

“…Moreover, a reduced quantity of mitochondrial DNA, but not genomic DNA, has been reported in Day 7 blastocysts from mares older than 16 years of age compared to younger counterparts, suggesting a reduction in mitochondria/cell ratio in old mares’ blastocysts [ 23 ]. Taken together, these alterations could lead to the alterations in embryo mobility and/or day of fixation that have been observed in some studies [ 9 , 28 ].…”

“…The effect of maternal age on embryo size is not so clear, as studies demonstrated a reduction of embryo diameter in old mares at several developmental stages [ 24 – 28 ] while others did not detect any effect [ 9 , 13 , 25 , 29 ] of maternal aging on embryo size. In these studies, however, the developmental stage was not uniform and the method to measure embryo size could be different (direct measurement or using ultrasonography).…”