Embryo transfer (ET) is an increasingly important tool for improving production efficiency and accelerating genetic progress in beef cattle. As with any technology, the success of ET is influenced by several factors. One may argue that pregnancy outcomes following ET should be greater than those obtained with insemination, considering that ET bypasses several critical steps of the reproductive process, especially in the cow’s uterus, including ovulation, fertilization, and early embryo development. However, important biological differences exist between embryos produced under natural conditions and those produced by hormonal stimulation or in vitro. Even high-quality embryos can result in poor pregnancy rates if recipient selection, synchronization, embryo handling, or transfer technique are inadequate. This article highlights three key aspects that you should understand to improve pregnancy in beef cattle: the recipient, the embryo, and the technique.
The recipient
Recipient management is one of the most important factors in the success of ET. Many producers prefer using heifers as recipients because they reduce challenges associated with calf management. However, heifers may be at greater risk of dystocia, and their maternal ability remains unknown compared with that of mature cows. Therefore, using mature cows may help reduce the risk of dystocia and provide greater confidence in the cow’s future maternal ability.
In females in poor nutritional condition, hormonal changes can disrupt normal estrous cycles and reduce fertility. Excessive body condition can also reduce reproductive performance by negatively affecting oocyte quality, embryo development, and fetal survival. Body condition should be monitored and managed throughout the year, avoiding major dietary changes during the 45 days before and after ET.
From a health standpoint, the ideal recipient should be negative for enzootic bovine leukosis, Johne’s disease, bovine viral diarrhea, anaplasmosis, and neosporosis. These diseases can negatively affect pregnancy, fetal development, and calf health. Also, internal and external parasites should be controlled, and recipients should be maintained under an appropriate vaccination program.
Recipients should be examined before synchronization for uterine diseases and for ovarian pathologies. Also, careful evaluation of the cervix, including its size and shape, is extremely important.
Good hygiene during synchronization procedures is important. Applicators for intravaginal devices should be disinfected between cows, and a new needle should be used for each animal to help minimize the risk of disease transmission. With hormones, always follow label instructions for proper dosage and storage recommendations.
Synchronized recipients should be carefully managed and kept away from bulls, since many females will be in estrus simultaneously, and accidental natural breeding may occur. Recipients that exhibit visible signs of estrus during fixed-time ET protocols usually achieve higher pregnancy rates than those that do not.
Temperament can have important effects on growth, health, and reproductive performance and should also be considered when selecting recipients for ET programs. In general, calmer recipients tend to achieve greater pregnancy, calving, and weaning rates than more excitable animals.
The embryo
Embryos used in cattle ET programs can be produced either in vivo or in vitro. There are significant differences in pregnancy success among embryo types. In general, several research studies comparing pregnancies established with both techniques have reported pregnancy rates 10% to 40% lower for in vitro-produced embryos. Currently, this difference appears smaller, but it remains a key factor to consider.
In both systems, embryos can be transferred fresh or frozen in liquid nitrogen and stored for future use. Cryopreservation is associated with lower pregnancy rates. Across different studies, pregnancy per ET in cows receiving cryopreserved embryos has been approximately seven percentage points lower than in cows receiving fresh embryos.
The technique
The ET procedure requires careful attention to embryo handling, cleanliness, recipient manipulation, and accurate embryo deposition within the reproductive tract.
A good ET technique depends heavily on adequate facilities and proper animal restraint. Excessive animal movement, poor restraint, or inadequate chute systems can make the procedure more difficult, increase manipulation of the reproductive tract, and potentially reduce pregnancy success.
During thawing, the straw should be protected from direct sunlight and wind. This does not mean producers need a sophisticated laboratory setup at the ranch; however, making every effort to provide appropriate conditions can help improve pregnancy results.
Final take-home message
Embryo transfer is a powerful reproductive tool that can accelerate genetic progress and improve productivity. However, the success of an ET program depends on much more than embryo quality alone. Proper recipient selection, good herd health, adequate nutrition, effective synchronization, low-stress management, careful embryo handling, and good transfer technique all play critical roles in achieving consistent pregnancy success.
Remember, the difference between average and excellent results is often found in the small details.
Photo by Molly Sloan