Embryo transfer in cattle has gained considerable popularity with seed stock beef producers. While most modern applicable embryo transfer technology was developed in the 1970s and 1980s, the history of the procedure goes back considerably farther. ‘‘Walter Heape performed the first embryo transfer in Angora rabbits in 1890’’ (J. C. Remsberg, ‘Herdsmen and vets benefit from E. T. training’). ‘‘Embryo transfer in livestock began in the 1930s with sheep and goats, but it was not until the 1950s that Jim Rowson at Cambridge, England reported successful embryo transfers in cattle and pigs’’ (Bryan M.
‘Reproduction and the Science in Cambridge’). The first commercial embryo transfers (ET) in the United States were done in the early 1970s. Initially, embryos were recovered from valuable donors and transferred to recipient animals using surgical procedures. It was not until current non-surgical methods were developed in the late 1970s, the process became more affordable and the practice in general has grown in popularity. Current technologies have taken this a step further with successful cloning of embryos creating genetically identical animals. The reproductive potential of each normal newborn calf is enormous.
There are an estimated 150,000 potential “eggs” or ova in the female and countless billions of sperm produced by each male. By natural breeding, only a fraction of the reproductive potential of an outstanding individual can be realized. ‘‘The average herd bull will sire anywhere from fifteen to fifty calves per year and the average cow will have one calf per year’’ (John W. ‘what’s a good bull really worth? ’). With artificial insemination (AI), it is possible to exploit the vast numbers of sperm produced by a genetically superior bull, however the reproductive potential of the female has been largely unutilized.
‘‘She will produce an average of eight to ten calves in her entire lifetime under normal management programs” (Marlboro M. ‘The Cow-Calf Operation’). Like artificial insemination has done for the bull, embryo transfer is a technique that can greatly increase the number of offspring that a cow can produce. It has been said that to dramatically improve the genetic base of a given cow herd it will take ten to twenty years to accomplish using only natural service. Incorporating AI can see these improvements in seven to eight years. “Through the use of an aggressive ET program this change is accelerated to four to five years” (Marlboro M.
‘The Cow-Calf Operation’). Largely purebred breeders have implemented the use of ET in the beef industry with some growing use by show calf breeders. ‘‘The breeders who have utilized ET have been pursuing these basic goals: to improve genetic selection by increasing the number of progeny from females that are either proven or perceived to be superior under any number of criteria, to multiply the number of cattle in a program in order to expand the herd, or to meet market demands’’ (Dr. Doug M. ‘Embryo Transfer in Beef Cattle’). There have been additional reasons given to rationalize the use of ET.
Supply and demand will always result in semen with increased value. ET will allow a breeder to generate more offspring from rare and valuable female embryos. Current technologies even allow for the application of sexed semen and embryos to give further control over the selection process. It has also been stated that ET will increase the accuracy of selection traits. Even with the use of ET, cows will have fewer progeny than bulls, which results in breeding values with lower accuracies. ‘‘The breeder must keep in mind that the performance of ET calves is partially reflected by the milking ability of the recipient female’’ (Drew C.
‘Embryo Transfer and American Milking Devon Cattle’). Therefore, performance on ET calves is not directly credited to the performance evaluation of the donor female. However, the natural progeny from ET calves will eventually contribute to the original donor’s Expected Progeny Differences (EPDs) at a later date. Whatever the stated reason, ET has had a significant impact on the beef industry. Take for instance the Angus breed. Registrations of Angus cattle over the past 15 years indicate a substantial increase in the use of ET. ‘‘In 1987, 3. 6 percent (5,105 head) of all calves registered in the Angus breed were a result of embryo transfer.
In 2002, 25,093 calves resulting from ET were registered. This was 8. 9 percent of all calves registered’’ (Monette T. ‘Rancher uses embryo transfers to obtain ‘right kind of cattle’). While Angus is one of the largest breeds in the United States, similar numbers have been documented in other breeds as well, thus we know that the popularity is across the industry and has been recognized as an effective means for retaining exceptional genetics. References Bryan M. , “Reproduction and the Science in Cambridge. ” April 8, 2011, www. hps. com. ac. uk Dr. Doug M.
, “Embryo Transfer in Beef Cattle. ” June 15, 2011, www. southwestanimalhealthcentre. ca Drew C. , “Embryo Transfer and American Milking Devon Cattle. ” June 29, 2007, www. milkingdevons. org J. C. Remsberg, “Herdsmen and vets benefit from E. T. training. ” Sunday, 29 August 2010, www. progressivedairy. com John W. , “What’s a good bull really worth? ” March 2000, www. noble. org Marlboro M. , “The Cow-Calf Operation. ” April 27, 2012, www. thepioneerwoman. com Monette T. , “Rancher uses embryo transfers to obtain ‘right kind of cattle’. ” April 10, 2003, www. countryworldnews. com