Interpretive Summary: Embryo and cow factors affecting pregnancy per embryo transfer for multiple service, lactating Holstein recipients
By: Dr. Emily Taylor
Embryo transfer has become a widely used reproductive technique in the cattle industry. Ultimately, this gives producers a way to optimize performance by propagating the best genetics in the herd. Obtaining success while utilizing embryo transfer highly depends on both the quality of the embryo and the recipient animal. The current study evaluated embryo and cow factors that affect pregnancy per transfer in cows predisposed to infertility. Specifically, researchers wanted to determine whether pregnancy success after embryo transfer during heat stress in multi-service Holstein cows was dependent on characteristics of the embryo or the recipient.
Multiparous and primiparous lactating Holstein cows with at least two previous inseminations were used as recipient animals. During the heat stress season, a DoubleOvsynch estrous synchronization protocol was utilized, and cows were inseminated with an embryo 8 d following the last GnRH injection. Female embryos were produced in vitro and were cultured with either 0.0 (control) or 1.8 mM choline chloride and either transferred to a recipient fresh or frozen. Embryo type (frozen vs. fresh, choline vs. control, unknown breed vs. control + choline) and characteristics of the recipients were evaluated.
Successful pregnancy diagnosis was dependent on whether the embryo was fresh or frozen and whether the recipient had been previously diagnosed with metritis. Recipients receiving a frozen embryo had a lower pregnancy rate (3/43; 7%) than recipients receiving a fresh embryo (32/120; 26.7%). These results, however, were expected, due to previous research that has reported poor survival of in vitro produced embryos frozen using ethylene glycol. Cows previously diagnosed with metritis in the early postpartum period (2/28; 7.1%) also had lower conception rates. Parity, days in milk, milk production, retained placenta and mastitis had no effect on pregnancy. In addition, choline had no effect on the ability of the embryo to develop to the blastocyst stage.
In conclusion, the use of frozen embryos produced in vitro and recipients that were diagnosed with metritis reduced conception rates in cows during the heat stress season.
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