Friday, May 5, 2017

Selecting Recipients for Embryo Transfer

For commercial dairies looking to increase herd progress and improve their overall bottom line or purebred operations striving to produce the next great cow or bull, embryo transfer (ET) and in-vitro fertilization (IVF) programs are becoming increasingly common. Technologies, such as donor aspiration and IVF lab techniques, are contributing to the popularity of ET and IVF programs among many types of operations.

To establish an effective and efficient ET or IVF program, a dairy’s management team must consider both the donors and the embryo recipients. Selection and care of elite genetic merit donor animals is critical for obvious reasons, but the selection and maintenance of recipients has significant implications too. Selecting recipient animals based on health, genetics and fertility – and maintaining
optimal conditions throughout the pregnancy – results in more high genetic merit calves on the ground.

Consider these factors when selecting and caring for embryo recipients:

Health. The basics of a healthy recipient are like that of the donor; she must be reproductively and
nutritionally sound. Heifers serving as recipients should have reached puberty, have a sound reproductive tract and have exhibited a first heat. Ideally, cows should have calved without any problems and be free of ovarian cysts, metritis or other issues. As a general rule, recipient candidates should be on a good nutritional plane and have proper body condition to support a healthy pregnancy.

Genetics. The genetics of the recipient animal have often been disregarded since she is “only carrying the embryo.” Donors are selected based on their high genetic merit, but those same traits are not applicable to recipients. Instead, it is important to consider traits which might contribute to getting the most calves on the ground.

When looking at a group of lower genetic merit animals as potential recipients, the dairy management team should sort those animals by traits that can contribute to conception and calving rate. A reliable Daughter Stillbirth (DSB) and Daughter Pregnancy Rate (DPR) evaluation can more accurately determine which animals should be used to carry embryos of high genetic value with the most success.

Fertility. Numerous studies show conception rates in dairy cattle are typically higher when heifers
are used as recipients versus cows. This is true for several reasons. First, heifers do not have the lactational stress cows do, particularly first lactation cows which are transitioning for the first time and still growing to reach their mature size. Also, heifers typically have less reproductive issues such
as cysts or infections from a hard calving. However, using only heifers as recipients is usually not practical or viable either, and cows can make perfectly acceptable recipients.

Consider this scenario. Many dairies are genomic testing their females, and often cull older, low genetic merit cows in favor of younger, high genomic animals. Still, these older cows typically produce quite a bit more milk than their 2-year-old counterparts. In this scenario, it can make sense to use older, lower genetic merit cows as recipients. By serving as an embryo recipient, the cow gives birth to a valuable calf and remains in the herd contributing significant pounds of milk. When selecting which older cows should serve as recipients, DPR and DSB are again the traits on which to sort them.

In conclusion, as ET and IVF continues to become more common in strategic breeding programs, strive to use healthy heifers or lower-ranking cows with desirable DPR and DSB values to carry high value pregnancies. Higher genetic merit females can then be used as donors or bred with more valuable semen. Ultimately, the genetic progress made through ET and IVF can lead to profitable future generations and dollars in the producer’s pocket.

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