Cellular damage suffered by equine embryos after exposure to cryoprotectants or cryopreservation by slow-freezing or vitrification.

REASONS FOR PERFORMING STUDY: Equine embryos are cryopreserved by slow-freezing or vitrification. While small embryos (<300 µm) survive cryopreservation reasonably well, larger embryos do not. It is not clear if slow-freezing or vitrification is less damaging to horse embryos. OBJECTIVES: To compare the type and extent of cellular damage suffered by small and large embryos during cryopreservation by slow-freezing vs. vitrification. STUDY DESIGN: Sixty-three Day 6.5-7 embryos were subdivided by size and assigned to one of 5 treatments: control, exposure to slow-freezing or vitrification cryoprotectants (CPs), and cryopreservation by either technique. METHODS: After thawing/CP removal, embryos were stained with fluorescent stains for various parameters of cellular integrity, and assessed by multiphoton microscopy. RESULTS: Exposing large embryos to vitrification CPs resulted in more dead cells (6.8 ± 1.3%: 95% confidence interval [CI], 3.1-10.4%) than exposure to slow-freezing media (0.3 ± 0.1%; 95% CI 0.0-0.6%: P = 0.001). Cryopreservation by either technique induced cell death and cytoskeleton disruption. Vitrification of small embryos resulted in a higher proportion of cells with fragmented or condensed (apoptotic) nuclei (P = 0.002) than slow-freezing (6.7 ± 1.5%, 95% CI 3.0-10.4% vs. 5.0 ± 2.1%, 95% CI 4.0-14.0%). Slow-freezing resulted in a higher incidence of disintegrated embryos (P = 0.01) than vitrification. Mitochondrial activity was low in control embryos, and was not differentially affected by cryopreservation technique, whereas vitrification changed mitochondrial distribution from a homogenous crystalline pattern in control embryos to a heterogeneous granulated distribution in vitrified embryos (P = 0.05). CONCLUSIONS: Cryopreservation caused more cellular damage to large embryos than smaller ones. While vitrification is more practical, it is not advisable for large embryos due to a higher incidence of dead cells. The choice is less obvious for small embryos, as vitrification led to occasionally very high percentages of dead or damaged cells, but a lower incidence of embryo disintegration. Modifications that reduce the level of cellular damage induced by vitrification are required before it can be considered the method of choice for cryopreserving equine embryos.

Efficacy of transvaginal ultrasound-guided twin reduction in the mare by embryonic or fetal stabbing compared with yolk sac or allantoic fluid aspiration.

Transvaginal ultrasound-guided pregnancy reduction (TUGR) is a procedure described for the management of twins post-fixation in the horse. Success rates are often disappointing but are reported to be more favorable for bilaterally situated twins and when intervention takes place before day 35 of gestation. This study aimed to determine whether stabbing the embryo/fetus rather than aspirating conceptus fluids improved the likelihood of success, measured as the birth of a normal live singleton foal. Data from 103 TUGR interventions were analyzed by logistic regression analysis; method of treatment, relative conceptus location (i.e., uni- vs. bilateral), and stage of gestation were included as interdependent factors that potentially influence the outcome. Overall, 34/103 (33%) TUGR interventions resulted in a single live foal. There was no significant difference (P = 0.14) in the outcome between TUGR based on fetal stabbing (12/28: 42.9%) versus fluid aspiration (22/75: 29.3%). There was also no significant influence (P = 0.11) of the conceptuses being located unilaterally (19/65: 29.2%) versus bilaterally (15/38: 39.5%). However, TUGR was numerically more successful (P = 0.05) when performed ≤ Day 35 of gestation (21/53: 39.6%), as opposed to > Day 35 (13/50: 26%). Day 45 may represent an even more critical time point because only 2 out of 15 TUGRs (13.3%) performed beyond this day resulted in the birth of a live foal, compared with 11/35 (31.4%) performed between Days 36 and 45. Although the numbers are low, this suggests that TUGR is not the method of choice for reducing > Day 45 twins. Four pregnancy losses were recorded 1 to 7 months post-TUGR (4/38: 10.5%), and although it is tempting to attribute the losses to TUGR, this rate of late gestation pregnancy loss is normal. We conclude that TUGR by fetal stabbing does not offer significant advantages over fluid aspiration. However, TUGR should be performed before Day 35 of gestation and is considered primarily a salvage procedure to be used when re-breeding is not a viable alternative.

Maternal age and parity influence ultrasonographic measurements of fetal growth in Dutch Warmblood mares.

Ultrasonographic examination of the equine fetus in mid-late gestation is usually performed only if there are concerns about fetal or maternal health. Even then it is difficult to determine whether development is 'normal' for gestational age because the reference values include considerable error margins. This study examined maternal factors that influence fetal growth with the aim of producing more precise late gestation fetal growth curves for Dutch Warmblood horses. Fetal development was monitored at 2-week intervals from day 100 of gestation until term in 32 mares ranging from 4 to 18 years in age; seven of the mares were primiparous. Transrectal and/or transabdominal ultrasonographic measurement of the fetal eye orbit, cranium, aorta, heart rate and of the combined thickness of uterus and placenta (CTUP) were performed using a portable ultrasound machine equipped with 6 MHz linear and 3.5 MHz curved array probes. During days 100-250 of gestation, the CTUP was thicker in primiparous than multiparous mares (p<0.05). After day 220 the maximum cross-sectional area, but not diameter, of both the eye orbit and cranium were also greater in primiparous than multiparous mares (p<0.05). Fetal aorta diameter was not influenced by parity but was affected by maternal age, being smaller in mares > or =15 years of age than younger animals (p<0.05). Only biparietal cross-sectional surface area and aorta diameter increased linearly throughout late gestation. However, even allowing for the effects of parity and maternal age, the late gestational variation in fetal size is such that serial measurements may be required to definitively identify abnormal development.