Methods to enhance embryo quality and recovery rates in superovulated beef cows
Tyler M. Dohlman
Methods to enhance embryo quality and recovery rates in superovulated beef cows were investigated. In the first study, uteri from superovulated heifers on day of recovery were harvested immediately following exsanguination and sectioned into 3 segments per horn plus the oviduct (8 sections per total uterus). Each section was thoroughly flushed through individual filters, searched and evaluated. Sectioning of the uterine horns impacted location of embryos with the majority of embryos located in the tip and middle third of each horn. In comparing these two sections, a greater percentage of the embryos were in the tip than in the middle third. Interestingly, embryos were recovered in both the oviduct and the base of the uterine horns. Based on these data, at time of embryo recovery, an embryo transfer (ET) practitioner should focus their recovery efforts towards the tip and middle third of the horns and potentially incorporating the body of the uterus to be include all potential embryo locations.
In the second study, effects of endogenous progesterone (P4) concentrations on embryo production were evaluated. Beef cows were superovulated following a CIDR-based presynchronization coupled with ultrasound-guided dominant follicle ablation (DFA). Comparison of high progesterone (HP) concentrations to low progesterone (LP) concentrations was achieved by administration of prostaglandin F2α (PGF) at DFA to the LP group while HP maintained their CL during superstimulation. Superovulation protocol included decreasing dosages of follicle stimulating hormone twice daily over 4 days and timed artificial insemination performed twice (12 hours apart). A greater proportion of quality grade 1 embryos were recovered from the LP cows compared to the HP cows, which had a greater number of quality grade 3 and 4 (degenerate) embryos. Additionally, a greater proportion of embryos recovered were developmental stage 6 and 7 in the LP cows. It should be noted, however, that more total embryos were recovered from HP than LP cows. There were no differences in total transferrable quality embryos between treatments.
A third study was designed to evaluate the effects of stage and grade of embryos on embryonic sex. In vivo-derived embryos from d 7 superovulated recoveries were biopsied using a micromanipulator with a microsurgical blade and the sex was determined using PCR techniques. Despite differences in developmental stage between embryos, they were not found to impact sex determination. However, differences in quality grade impacted embryonic sex determination. Specifically, a greater proportion of quality grade 2 embryos were female while a greater proportion of grade 1 embryos were males.
In application of these studies, a practitioner with a cattle producer who wants to maximize embryo output and has recipient cows available for transferring fresh embryos at time of recovery could superstimulate the donor under the influence of uninhibited P4 concentration. This would be followed with recovery on d 7 with placement of the catheter at the base of each horn for horn flushing while potentially incorporating the uterus during the recovery to perform a thorough flush of the entire uterus. Ideally, this scenario should yield a greater number of embryos, however quality may be compromised, yet could be transferred fresh into recipients. Additionally, with the potential for an increase in quality grade 2 embryos from the recovery, our data suggests the potential for an increased number of heifer calves. On the other hand, if a seed stock producer wants to cryopreserve the best embryos from their donor, our data would suggest implementing a superovulation protocol under the influence of LP, followed by horn flushing method in which the catheter is placed at the base of each horn on d 6 -7. Our results would suggest this recovery would produce a greater proportion of freezable, grade 1 embryos which could increase the probability of producing bulls.