Are Efficiencies in ET Occurring
by Barb Baylor Anderson for Angus Productions Inc.
NASHVILLE, TENN. (Aug. 6, 2010) — When you consider all of the variables involved in embryo transfer (ET) with donors, recipients, the embryos and practitioners, much can influence the potential for success. John Hasler, Bioniche Animal Health Inc., provided an update on associated ET efficiencies during the Applied Reproductive Strategies in Beef Cattle (ARSBC) Conference in Nashville, Tenn.
"The actual success rates within the ET industry — as measured by the mean number of embryos recovered per donor or by conception rates following embryo transfer — have changed very little over the years," Hasler said. "Nevertheless, fundamental principles related to donor and recipient management and to ET procedures do profoundly influence the level of success."
Within the beef industry, Hasler noted, success rates in well-managed cattle herds already are quite high. Recent improvements involve only small, but important, increments.
"In a 1992 review I stated, 'There have been no significant improvements in techniques for the superovulation of cattle in the last 15 years,'" he said. "Eighteen years later, that statement remains largely true. For example, data show the number of embryos collected from beef cattle has not substantially changed. Embryo yields per donor remain in the range of 5 to 7."
Hasler said research finds embryo production is similar whether donor superovulation is initiated during mid-cycle or following the insertion of a CIDR at a random stage of the estrous cycle. He did add, however, that the use of CIDRs has led to a shorter inter-superovulation interval, so more embryos are produced per unit of time. At the same time, superovulation efficacy has not been influenced much by different FSH preparations used over the years.
Conference proceedings outline a number of other donor and recipient variables not covered by Hasler during his presentation. One area he did highlight with regard to the process is research that clearly shows sperm quality, sperm number and the timing of insemination are closely correlated with fertilization success in superovulated cattle. Most superovulated donors are inseminated with one unit of semen at 12 and at 24 hours post onset of estrus.
"Of equal importance to this fertilization is the ability of the embryos to establish pregnancies following transfer into recipients," he said. "Even after fertilization and development into morphologically good-quality embryos, differences in pregnancy rates relative to sperm quality and among different sires have been demonstrated."
Hasler addressed cryopreservation, observing that 68% of embryos are frozen today, which makes development of a reliable process a necessity. Many are now frozen in ethylene glycol, because the embryos require only one step of a warm water thaw prior to use.
"The highest conception rates in bovine ET are achieved with fresh, in vivo-derived embryos," he noted. "Frozen and manipulated embryos and embryos resulting from various in vitro systems, including cloned and transgenic embryos, are all associated with lower conception rates."
In addition to progesterone, a number of drugs and hormones have been used to try to increase conception rates in recipients. For the most part, those treatments have not done the job. The skill of technicians also can play a role. Hasler said a number of studies show both non-return rates and pregnancy rates vary widely among experienced technicians under similar conditions.
"Luck plays a part in the outcome of some ET procedures," he said. "Sometime opportunities exist for ET practitioners to make a meaningful contribution to improving or changing certain management programs. In other cases, change is either not welcome or not possible. Practitioners must make the best of the situation at hand. Donor and recipient quality and management are keys to success and the most important factors for ET."
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