Effect of breeding season and age on follicular dynamics and hemodynamics in embryo donor mares subjected to luteolysis after embryo flushing

Abstract

Background: Mares are the only companion animal simulating women in the large diameter of their follicle, the effect of aging on reproduction and even mares are more sensitive to summer heat stress as they can sweat like human. Aim: The current study aimed to investigate the dominant and subordinate follicular dynamics and hemodynamics and circulating ovarian hormones in embryo doner mares spontaneously ovulated, after inducing ovulation using human chorionic gonadotropins (hCG), and after inducing luteolysis using prostaglandin F2α (PGF2α) following embryo flushing with studying the differences age (young vs senile) and season (cold vs hot). Methods: Spontaneous estrous cycles of young mares (<10years; N=6) or senile (>20 years; N=5), cold season (October to April), hot season (May to August), after inducing ovulation using hCG, and after inducing luteolysis using PGF2 α were studied each other day using Doppler ultrasound with blood sampling. Estradiol (E2), progesterone (P4), nitric oxide (NO), total cholesterol, and lactate dehydrogenase (LDH) were measured in blood serum. Results: A decrease in the dominant follicle antrum diameter (P>0.05) and LDH (P=0.016) was observed after inducing luteolysis. Both hCG and PG increased dominant follicle area (P=0.0001), antrum area (P=0.001), perimeter (P=0.001), granulosa area (P=0.0001), Cholesterol (P=0.0001), NO (P=0.0001), and E2 (P=0.0001). The hot season increased (P=0.0001) dominant follicle area, antrum area, perimeter, color area, granulosa area, LDH, cholesterol, NO, and E2 but decreased the circulatory % (P=0.0001). Senile mares had lower dominant follicle area (P=0.002), antrum area (P=0.0001), granulosa area (P>0.05), LDH (P=0.001), cholesterol (P=0.0001), NO (P=0.0001), and E2 (P=0.0001) but higher circulatory % (P=0.0001) and color area %(P=0.023). The dominant follicle possesses the largest diameter, area, perimeter, granulosa area, and color area but the lowest circulatory % during spontaneous estrous cycles, after inducing ovulation, or luteolysis with significant effects of the Day of the spontaneous estrous cycles on their dynamics and hemodynamics. Conclusion: Senile mares can be used for as embryo or oocyte donners and during the hot season.