1. Investigación

Ovum pick-up (OPU) by transvaginal ultrasound guided follicle aspiration in mares is a common assisted reproductive technique used for oocyte recovery and in vitro production of horse embryos. There has been relatively little research into the factors influencing oocyte recovery in OPU from live mares. The objective of this study was to compare oocyte recovery and morphology of ultrasound-guided follicle puncture and aspiration in live mares and in postmortem excised ovaries, in order to validate an experimental model for research purposes of the efficiency of OPU in mares. Data from OPU performed in 12 mares from a commercial program (follicle numbers, oocyte recovery and oocyte morphology) were compared to that obtained from ultrasound-guided follicle puncture of 13 postmortem excised ovaries from slaughtered mares processed within 2 h of slaughter. In both groups, the OPU was performed by the same operator using the same equipment and OPU technique. The recovered oocytes per aspirated follicle was higher (P < 0.05) in the postmortem group (105/166, 63.2 %) than in live mares (138/261, 52.9 %). There was more (P < 0.05) expanded cumulus oocyte complexes in the postmortem than in the live mares (18 % vs. 2.9 %). Several oocytes (5 oocytes from 81 aspirated follicles) were found in the leaked fluid which overflowed during follicle flushing of postmortem ovaries. In conclusion, the higher recovery rate obtained in the excised ovaries and the finding of oocytes in the leaked fluid during OPU, suggests that there is still room for improvement in the in vivo OPU technique. Utilizing postmortem excised ovaries could offer an alternative for further research into factors affecting oocyte recovery and oocyte leakage during OPU procedures.

Two experiments were conducted in the Northern (UK) and Southern (Brazil) hemispheres to determine the effect of season (month of conception) on the development of supplementary CL (SCL) and the relationship with pregnancy loss. In experiment 1, 199 pregnancies were followed between Day 14 and term, to determine the number of SCL and pregnancy viability (Northern Hemisphere). From the 199 pregnancies, 178 were obtained from inseminations during the breeding season (March–September), while the rest, 21 pregnancies resulted from conceptions in the non-breeding season (October to February). Pregnancies conceived in the breeding season were more likely (P < 0.01) to have at least 1 SCL (75.8 %, 135/178) than pregnancies from the non-breeding season (33 %, 7/21). However, the pregnancy loss between Days 35 and 120 of pregnancy in mares with no SCL was similar (3.5 %, 2/57; P >0.1) than from mares with SCL (1.4 %, 2/142). In Experiment 2 (Southern Hemisphere), three groups of recipients were used based on their ovarian activity at the time of embryo transfer: Anestrus (n = 8), transitional (n = 7) and cyclic (n = 7) recipient mares. While all transitional and cyclic mares developed at least 1 SCL, only 50 % of anestrous recipients (4/8) developed SCL by 120 of gestation. In conclusion, the development of SCL in pregnant mares is influenced by the time of season of conception, therefore it appears to be regulated by the photoperiod and the endogenous seasonal variation in gonadotropin concentrations. Mares with no SCL were not at increased risk of pregnancy loss.

The effect of embryo reinsertion immediately after embryo flushing was studied. In Experiment 1, eight mares were used during 32 cycles (8 cycles in each group). For the first two groups, inseminated mares were flushed 8 days after ovulation and prostaglandin F2α was not administered: in group EF-ET (embryo flushing and embryo transfer) the embryo was reinserted in the same donor mare, while in the EF group, no further procedure was performed. In the third group (ET), non-inseminated mares (recipients) received a Day 8 embryo. Progesterone concentration was measured before EF/ET and 72 h after in the three groups. In Experiment 2, twelve mares were used during 17 cycles in two groups, EF-ET (n = 11) and ET (n = 6), as in Experiment 1, except that every mare was flushed 24 h after embryo transfer to retrieve the embryo. Fewer pregnancies resulted after transfer in EF-ET cycles (0/8, 0%) than in the ET group (6/8, 75%). Progesterone concentration decreased significantly (p = 0.05) 72 h after EF-ET but not in EF or ET cycles (p > 0.1). Three mares from the EF-ET showed full luteolysis and signs of endometritis. In Experiment 2, more (5/6; p = 0.08) grade 1 embryos were recovered in the ET compared to the EF-ET group (3/7); 4 embryos were graded 3–4 (were broken or had signs of degeneration) in the EF-ET group but none in the ET group. In both groups, capsule fragments were obtained as indicative of the presence of a recently destroyed embryo in the EF-ET (n = 3) and ET (n = 1) groups. Positive bacterial cultures were obtained in 2/11 and 1/6 embryo flushes from the EF-ET and ET groups, respectively.

The aims of this study were to determine the effect of the embryo flushing technique and the number of flushing attempts performed by operators of different experience on embryo recovery (ER). Ten non-lactating mares were inseminated with the same stallion in six cycles each (n = 60). Embryo flushing (EF) was performed 7–9 days after ovulation by three operators (OP; 20 EF cycles each): OP1 had performed >500 EF before the study, while OP2 and 3 had performed 0 EF. Each EF was performed with 2 flushing attempts (FA) using 1L of ringer's lactate “in-and-out” using two EF techniques: 1) uterine massage (UM): continuous ballottement and massage of the uterus per rectum during ringer lactate recovery, 2) gravity flow (GF): the ringer lactate was allowed to flow back without massaging the uterus. In both groups, 20 IU of oxytocin were administered at the second FA and the ringer lactate was allowed to remain in the uterus for 3 min before recovery. An extra FA was performed in each group using 0.5 L of ringer lactate and uterine massage. More embryos (P < 0.05) per ovulation were recovered in the UM (17/33, 0.51) than in the GF group (8/36, 0.22). For the UM group, 16/17 embryos (94.1 %) were recovered in the first FA, while only one embryo in the second FA (1/17, 5.9 %). In the GF group, 4 embryos were recovered in each FA. No embryo was found in the extra FA in the UM group, while seven additional embryos were found in the GF group (5/7 flushed by OP1; P < 0.05). The overall ER per cycle was 70, 40, and 45 % for OP1, 2 and 3, respectively. In conclusion, highest embryo recovery is achieved in EF performed with UM, with the majority of embryos being flushed in the first FA.

Background: PGF2α is commonly given at the end of embryo flushing (EF) to shorten the interval to the next oestrus and ovulation. Objectives: To determine the effect of repeated EF on plasma progesterone concentration, percentage of mares with endometritis, unwanted pregnancy and subsequent fertility in mares flushed without the use of PGF2α. Study design: Controlled experiments. Methods: Nine mares were inseminated in seven consecutive cycles (n = 63), to either perform an EF (n = 54) 7–9 days after ovulation or left pregnant (n = 9). PGF2α was not used to induce oestrus. Ultrasound examination and blood sampling were performed just before the EF and 72 h later to determine changes in progesterone concentration and signs of endometritis. Results: The overall percentage of positive EF/pregnancy was 55.5% (30/54) and 66.7% (6/9), respectively. The likelihood of pregnancy/positive EF in the first three cycles was 55.5% (15/29). This was not different (p > 0.1) from the fertility of the last four cycles (69.4%, 25/36). In five EF cycles (9.3%), mares had signs of endometritis and early luteolysis (progesterone <2 ng/mL) 72 h after EF. The reduction in progesterone concentration by 72 h after EF was greater (p < 0.05) for Day 9 (−2.3 ± 0.7 ng/mL) than Day 7 (−1.0 ± 0.8 ng/mL) or Day 8 (−1.3 ± 1.1 ng/mL) cycles. The progesterone concentration in non-flushed mares did not vary significantly during the sampled period (Day 7–12). There were 5 cycles in which the donor mare remained pregnant after the EF, although four were from a single mare. Main limitations: The mare population was limited to barren and maiden mares. The cycle order and operator allocation to each EF were not randomised. Conclusions: EF induces a subtle, but significant reduction in progesterone concentrations compared with non-EF cycles. However, the percentage of mares with EF-induced full luteolysis is low (9.3%). The fertility of mares after repeated EF without administration of PGF2α was unaffected; however, there is a considerable risk of unwanted pregnancy (5/27 = 18.5%) in donors from which an embryo was not recovered.