Reproductive patterns and follicular waves in postpartum lactating versus non-postpartum cycling mares

Follicular Dynamics and Pregnancy Rates during Foal Heat in Colombian Paso Fino Mares Bred under Permanent Grazing

No studies have evaluated the peripartum follicular dynamics resulting in foal heat under tropical environments. We aimed to assess retrospectively the peripartum follicular dynamics in Colombian Paso Fino mares that were inseminated at the foal heat, becoming pregnant or not. Records including follicular dynamics of pregnant mares prepartum and from foaling until foal heat ovulation were assessed in Colombian Paso Fino mares (CPF, n = 24) bred under permanent grazing in a tropical herd in Colombia. The number of ovarian follicles >10 mm before foaling and the largest follicle (F1) growth rate (mm/day) from foaling until the F1 reached the largest diameter (pre-ovulatory size) at the foal heat were assessed. Mares were inseminated at foal heat with 20 mL of semen (at least 500 million live spermatozoa) with >75% motility and 80% viability from a stallion of proven fertility. Ovulation was confirmed the day after follicles had reached the largest diameter. Quantitative data from follicular growth, the day at ovulation, from mares that became pregnant (PM) or not (NPM) at 16 days post-insemination were compared by one-way ANOVA, repeated measures ANOVA (follicle growth rate data) or Chi-square test (edema and cytology scores data). Epidemiological data, gestation length, and the number of follicles on third prepartum days did not significantly differ between PM and NPM (p > 0.05). Seventy-one percent of mares (17/24) got pregnant. Ovulatory follicles grew faster in the NPM group (n = 7), which ovulated between the seventh and ninth postpartum days, compared to PM (n = 17), which ovulated between the 11th and 13th postpartum days. Pre-ovulatory follicle diameter in PM (48.57 ± 0.8 mm) was significantly larger than in NPM (42.99 ± 1.0 mm) (p < 0.05). In addition, the PM edema score (2.93 ± 0.32 mm) on ovulation day was significantly lower (p < 0.05) than NPM (4.47 ± 0.05 mm). First postpartum ovulation occurred at 12.6 ± 0.3 and 8.5 ± 0.4 days (p < 0.05) in PM and NPM, respectively. Colombian Paso Fino mares bred under permanent grazing under tropical rainforest conditions with no foaling or postpartum complications showed a 71% gestation rate when inseminated at foal heat when ovulation occurs between the second and third postpartum week.

Structural and Functional Dynamics of the Ovary and Uterus during the Estrous Cycle in Donkeys in the Eastern Caribbean

Eight non-bred, non-pregnant, regularly cycling Caribbean jennies were examined daily via transrectal ultrasound to define the ovarian and uterine dynamics during four consecutive estrous cycles. Blood samples were collected every other day for progesterone analysis. The mean (±SD) overall inter-ovulatory interval across all donkeys and cycles was 22.93 ± 1.99 days. The maximum follicular diameter was 34.6 ± 2.9 mm. A two-wave pattern was evident in 97% (30/31) of the cycles. The emergence of the future dominant follicle and the largest subordinate follicle of the major primary wave coincided on Day 5.7 ± 3.6 post-ovulation, whereas the secondary wave emerged on Day 19.8 ± 2.9 during estrus of the previous cycle or early diestrus. The secondary wave was often minor (93%, 28/30 cycles). Follicular deviation occurred 8.2 ± 1.4 days before the subsequent ovulation. Luteal volume increased for the first four days after ovulation and reached a maximum volume of 8.5 ± 2.7 mm3 at Day 5.4 ± 0.4, before gradually regressing after Day 15. Serum progesterone concentration increased from Day 1 after ovulation, peaking at 27.0 ± 9.6 ng/mL between 7 and 10 days after ovulation. Progesterone concentration dropped precipitously around Day 15 after ovulation and was below 2 ng/mL around Day 17 ± 2. A day effect (p < 0.0001) was observed for corpus luteum’s volume, progesterone concentration, and uterine tone, but not for endometrial edema (p > 0.05). This study helps to clarify and define normal estrous characteristics of jennies in the Eastern Caribbean.