Embryo transfer in cattle has gained considerable popularity with seed stock beef producers. While most modern applicable embryo transfer technology was developed in the 1970's and 1980's, 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.
