Ch. 6— Maintaining Animal Diversity Offsite • 149 



Photo credit American Breeders Semce 



Liquid nitrogen storage vessels (above) contain enough frozen bull semen to inseminate 4.5 million cows. 

 Liquid nitrogen maintains the temperature at -196° C (-320° F). 



of the frozen material. Samples from current 

 populations would likewise periodically be 

 added to the frozen store to retain new vari- 

 ants produced by natural selection or mutation. 

 This process would be particularly important 

 in domestic populations, in which selection 

 could make preserved individuals economically 

 obsolete. 



Breeding Technologies 



The goals of a propagation program can be 

 defined in terms of how much genetic diver- 

 sity is to be maintained and for how long. Ta- 

 ble 6-3 shows the number of animals required 

 to ensure retention of various proportions of 

 genetic diversity for subsequent generations. 

 Ideally, all of the genetic diversity present in 

 the source population would be maintained in- 

 definitely in the captive population. Table 6-3 



Table 6-3.— Captive Animals Required for a 



Fixed Proportion of Genetic Diversity 



Over a Number of Generations 



Percentage of .. ^ z 



genetic diversity Number of generations 



maintained 50 100 200 1,000 



50 36 72 145 722 



75 87 174 348 1,738 



90 238 475 949 4,746 



95 488 975 1,950 9,748 



99 2,488 4,975 9,950 49,750 



SOURCE: Adapted from D.R. Notter and T.J, Foose, "Concepts and Strategies 

 To Maintain Domestic and Wild Animal Germ Plasm," OTA commis- 

 sioned paper, 1985. 



suggests that this goal (i.e., retention of 99 per- 

 cent for 1,000 generations) would require up 

 to 50,000 animals. These numbers are consist- 

 ent with the guidelines in table 6-1, which sug- 

 gests natural populations of fewer than 100,000 

 should be carefully monitored. 



