Ch. 6— Maintaining Animal Diversity Off site • 755 



Figure 6-2.— Embryo Transfer Flowchart 



Recipient 



Synchronizalion of Estrous Cycles 



Necessary steps in preparing donor and recipient animals 

 for embryo collection and transfer. 



SOURCE: Betsy Dresser, Director of Researcti, Cincinnati Wildlife Researcfi Fed- 

 eration, 1986. 



to be identified in most other species. Donors 

 are mated naturally or by artificial insemina- 

 tion, and fertilized eggs are collected from the 

 female tract (surgically and nonsurgically) and 

 transferred (surgically or nonsurgically) to the 

 recipient female. 



Development of embryo transfer techniques 

 is important to maintenance of genetic diver- 

 sity within captive populations, given the con- 

 siderations of transfer and disease control pre- 

 viously discussed. In addition, surrogate 

 mothers confer passive immunity to offspring 

 developed from transferred embryos. Thus, ani- 

 mals moved into new environments or re- 

 introduced to the wild may benefit from being 

 carried by mothers acclimated to the new envi- 

 ronment. 



Several more-advanced techniques, studied 

 primarily in domestic animals, hold consider- 

 able potential for all species: 



• Embryo Culture: This technique involves 

 maintenance of fertilized eggs outside the 

 body during the early stages of embryonic 

 development. The appropriate culture me- 



dia for development differ among species, 

 but reliable techniques to culture embryos 

 for up to 24 hours exist for cattle, rabbits, 

 mice, sheep, and humans. Successful em- 

 bryo culture is usually prerequisite to more 

 sophisticated in vitro embryo manipu- 

 lation. 



Embryo Storage: This technology involves 

 holding embryos in arrested development 

 for up to several days. Again, specific stor- 

 age media must be developed for each 

 species. Embryo storage procedures can 

 greatly facilitate transfer of embryos over 

 long distances and in vitro embryo manipu- 

 lation. 



In Vitro Egg Maturation: This technique 

 involves the culturing of immature eggs to 

 maturity. Coupled with in vitro fertiliza- 

 tion, this technique could dramatically in- 

 crease the number of offspring that a given 

 female might produce. The reproductive 

 lifetime of the female is also lengthened be- 

 cause ova suitable for culturing can be ob- 

 tained prior to sexual maturity as well as 

 after a female is no longer able to conceive 

 naturally. 



In Vitro Fertilization: In a few species, it 

 is possible to remove unfertilized ova from 

 a female, mix them with semen in vitro, 

 and produce fertilized ova that will develop 

 normally when transferred back into a fe- 

 male. In cases of unexpected death of ge- 

 netically valuable animals, ova can even 

 be collected from ovaries shortly after 

 death. 



Embryo Splitting: A single embryo can, 

 under the proper conditions, be split into 

 two or four, and each part can subsequently 

 develop into a live offspring. Although the 

 offspring are genetically identical, this 

 process allows a much larger number of 

 offspring to be produced from each embryo 

 collection. 



Interspecific Embryo Transfer: This in- 

 volves transfer of embryos between related 

 species. Thus, embryos of a rare species 

 could be carried to term by a female of a 

 more common species. This technology 

 has enjoyed some success, but much more 

 research is needed. To date, successful in- 



