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Embryo Transfer - Improving Bovine Pregnancy Rates
Unacceptable low pregnancy rates can be due to poor management practices of donors and recipients and not the often expected poor embryo technology. The most common practices causing stress can be divided into, incorrect condition of donors and recipients, transportation problems, rough handling of cattle, inadequate management of liquid nitrogen tanks and their contents, and unfortunately unknown causes.
When synchronizing recipients using the two shot prostaglandin (PG) system and only 30-40% show standing heat, that is the time to cancel the program. Usually after the second shot only 50-60% respond. In addition when those relative few recipients are implanted pregnancy rates are unacceptably low. These results are due to the demise of the corpus luteum (CL) by Day 21. Results such as these can be backed-up by a published study of Kunkel et al in Theriogenology in which pregnancy rates after artificial insemination are related to the physical condition of the cattle. For instance cows rated as a body score of thin #3 achieved a low 43% pregnancy rate, a #4 only achieved a 61% pregnancy rate, and a #6 achieved a very good 93% pregnancy rate, but as a fat #8 pregnancy rate was down to 50%. How many times are we presented with poor quality recipients, sometimes the rejects from the usual breeding program?
Shipping recipients immediately after transfer does not influence pregnancy rates. We had a chance to study this situation in our program at CSU. One client transported his donors and recipients from southern Colorado to Fort Collins, a 10 hour drive, while he slept we worked on his animals all day collecting and transferring embryos and then that night they were shipped back home. We compared embryo collection numbers from the donors and the pregnancy rates in the recipients to our resident donors and recipients and there were no significant differences.
Rough handling of donors and recipients will also yield poor results. This is thought to be due to increased release of cortisol, a stress hormone, which adversely affects other reproductive hormones leading to lower embryo collection rates, decreased quality of embryos, and lower pregnancy rates.
Another factor leading to disappointing results can be the management of liquid nitrogen tanks and the handling of frozen semen canes and straws. Considering the total costs of an embryo transfer program it is wise to evaluate the spermatozoa even if you just look for movement of sperm in a drop of the semen using the embryo stereozoom microscope itself. With these kinds of microscopes individual sperm cannot be observed, but in most cases out in the field movement is all that can be accomplished. Examples of damaged sperm can be excessive exposure of frozen straws when either changing tanks or selecting straws to use.
-Dr. Peter Elsden
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