A common failure in embryo transfer programs is the selection and preparation of recipients. I am often asked which breed should be selected for receiving embryos. To date there is no evidence that any Bos Taurus (British and European) breed is superior. However, many years ago we found Bos Indicus (African and Asian) cattle proved to be poor recipients but their crosses perform at a similar rate. Unfortunately, one-time, or first-time users of embryo transfer too often try using animals which have previously failed in their own breeding program with disappointing results. Sustaining programs select good quality animals resulting in consistent satisfactory pregnancy rates, e.g., 67% pregnancy rates transferring fresh embryos, and 50% for frozen thawed embryos initially graded as 1s and 2s. In one of our early frozen embryo programs we achieved 12% WEANED CALVES born when number 3 grade embryos were transferred.
A body score of 5 or 6 is optimum which can be achieved by feeding a comprehensive ration, comprised of at least a 12% protein and an all season mineral stock containing trace minerals. At Colorado State University we had a large herd of cross bred beef recipients fed good quality hay, minerals and no supplements and achieved a 65% pregnancy rate transferring embryo graded from 1 to 3. When we were offered Holstein heifers as recipients from a local feedlot we achieved a 70% pregnancy, but when we used failed recipients a second time still on a feed lot ration the pregnancy rate fell to 37%. They were too fat which results in difficult uterine palpation and demise of the corpus luteum by day 21. Minerals should be fed at least once a week, optimum intake is 4ozs. Special attention should be given to heifers and young cows as they can be energy deficient and the CL will disappear by day 21 and the pregnancy will be lost. Always remember the reproductive system is a ‘’luxury’’ and is the first to fail when some other factor is present. It is suggested that the normal nutrition levels should be increased about 2 to 3 weeks before embryos are transferred. Clean water is important and should be tested for high sulfates and nitrates.
Temperament is another factor to consider. They should remain in their own group to avoid establishment of a new pecking order when moved to a new group. Human-animal interactions can be detrimental when animals are treated inhumanely causing a release of a stress hormone which adversely affects reproductive hormones.
Shipping recipients after transfer is another question to consider. We had one client who shipped his recipients for 10 hours to us at night, then we transferred embryos that same day, and then they were shipped back that night. We took this opportunity to compare pregnancy rates with our own resident recipients, and we found that shipping on the day of transfer had no effect on pregnancy rate. However, recipients should not be moved from day 12 to 35 when maternal recognition occurs, and the embryo is attaching to the mother.
In conclusion use common sense with proven cattle management.
-Dr. Peter Elsden
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