Ch. 6— Maintaining Animal Diversity Offsite • 153 



T?,ss(is;rK?.r, :r ,^ \iiwr . .> ?r. iTKW/sSv'i'tS'a s.^ 



Box 6-D.— Embryo Transfer 



Embryo transfer is a well-established practice in the beef and dairy cattle industries. More than 

 200,000 transfers are performed annually throughout the world, mainly in the United States and Can- 

 ada. Although the technique was first used with beef cattle, half the transfers are now in dairy cattle. 

 The objective is to increase the number of offspring of cows with valuable genetic traits, such as 

 rapid rates of growrth and high levels of milk production. Using this procedure, one valuable cow 

 can produce on average 12 offspring a year. 



The procedure involves inducing superovulation in a donor cow using gonadotrophic hormones, 

 so that she will produce six to eight eggs rather than one. The cow is artificially inseminated with 

 semen from a valuable, high-performance bull, and the embryos are collected by nonsurgically flush- 

 ing the uterus after 6 to 8 days. Embryos that appear viable and healthy by microscopic examination 

 are transferred to recipient cows that are also at the sixth to eighth day of their estrous cycle. Nor- 

 mally one embryo is transferred to each recipient. 



Several new technologies hold promise of making the process more efficient and increasing its 

 usefulness to animal agriculture. Among these is the ability to freeze bovine embryos. This procedure 

 is currently used by most embryo transfer companies, and 25 percent of the transfers in the United 

 States are with frozen embryos. Survival of the embryos is not perfect, however: Transfer of unfrozen 

 embryos average a 60-percent pregnancy rate, while frozen and thawed embryos can be expected 

 to yield pregnancy rates of 40 to 50 percent. 



Another interesting development in this industry involves cloning bovine embryos. Once devel- 

 oped, this technique would allow the multiplication of large numbers of calves from one valuable 

 embryo. The cloned embryos could be frozen while other embryos from some clonal hues are tested 

 to determine if the line is of high value; valuable ones could be replicated using the frozen clones, 

 providing a powerful tool for Hvestock improvement. Several research stations are also experiment- 

 ing with inserting genes for specific productivity traits, such as growth, into embryos before transfer. 

 The apphcation of these new biotechnologies is expected to expand the size and usefulness of the 

 cattle embryo transfer industry. 



Although embryo transfer could also be a useful tool in swine production, much of the technology 

 and the industry are not yet well developed. In swine, embryos must be collected and transferred 

 surgically. And the embryos do not survive freezing with present techniques. This procedure there- 

 fore has received little use in the swine industry. In addition, the cost of surgically recovering em- 

 bryos is likely to preclude wide-scale use of this technology in the near future. 



Based on the use of embryo transfer in cattle, research on the applicability of this technology 

 for wild species was begun in 1981. Although the nonsurgical collection techniques are similar, work- 

 ing with exotic species entails several unique problems, such as the need to administer drugs by dart 

 or pole syringe and the need for anesthesia to perform even the simplest procedures. The ultimate 

 goal was to develop methods for using a common wild species (e.g., the eland antelope) as a surrogate 

 mother for a less common species (e.g., the bongo antelope). 



In 1983, an eland calf was born to a surrogate eland mother, becoming the first nondomestic 

 issue of a nonsurgical embryo transfer. A transfer involving a frozen embryo was accomphshed soon 

 thereafter. These successes were followed by attempts at interspecies transfer (i.e., a donor and sur- 

 rogate of different species). Initial efforts for an eland-to-cow transfer were unsuccessful. The eland, 

 however, proved to be a suitable surrogate mother for an embryo collected from a bongo. This first 

 documented nonsurgical embryo transfer between two different species of wild animals indicates 

 that embryos can be gestated by surrogates of different species, offering hope for the future of endan- 

 gered wildlife (figure 6-1). 



SOURCE: Adapted from materials provided by Dr. Neal First, University of Wisconsin and Dr. Betsy Dresser, Cincinnati Wildlife Research 

 Federation. 



