Ch. 9— Advances in Reproductive Biology and Their Effects on Animal Improvement • 1 73 
I lie dt'\ aiul applii ation ol ('(M tain 
kt‘\ lfrhiu)l()f'ies will alteft rt'laloil tei'hnol- 
ogies— e.g., the a\ ailahiliU’ of reliable estrus 
detection and estrus synchronization methods 
should inci'ease the use of Al and emhr\o trans- 
fer in beef anti tlair\ cattle, thereby spreatling 
genetic advantage. Further pi'ogress in the 
freezing of eml)ryos sliould facilitate the genetic 
ev aluation of cows and heifers. 
Other ti'ends that mav influence U>chno- 
logical change include the shifting av ailahilitv of 
I'eseai'ch funds, changing consumer tastes, and 
gi’ovv th of rt'gulations (for instance, stricter con- 
trols on environmental (|uality or hormonal 
treatments). Th(‘ e.xpansion of an animal rights 
movement may influence the degree to vvliich 
confinement housing, and therefore controlled 
hret'ding, is acceptable. .And increased energy 
costs may (‘ithei- encoui'age development of the 
technologies (through efforts for greater effi- 
citMicv ) or discourage them (through greater use 
of foi'age and e.xtensive systems). 
Technologies 
Sexual reproduction is a game of chance. Be- 
cause s[)erm and ova each contain only a ran- 
dom half of the gtMies of each paiaMit. tlie num- 
ber of |)ossihle combinations that can result is 
nearlv infinite. Some pi-og(MU aiv likelv to sur- 
vive and reproduce: others die either before 
birth or vv ithout ()roducing offs|)ring. 
rhe great variation achieved through sexual 
reproduction produces certain animals that 
satisfy the needs and desires of the breeder far 
more than others. On the other hand, the off- 
spring of these outstanding animals are usually 
less so than their parents, although they are 
generally still ahov e av erage. 
Animal breeders hav e inv ested great effort in 
improv ing succeeding generations of domestic 
animals, both by limiting the differences due to 
the chance associated vv ith sexual reproduction 
and by taking adv antage of the favorable combi- 
nations that occur. E.xamples of these efforts in- 
clude keeping records, establishing progeny 
testing schemes, amplifying the reproduction of 
outstanding indiv iduals by .A I and embryo trans- 
fer, and establishing inbred lines to capitalize on 
their more reliable ability to transmit charac- 
teristics to their offspring. 
Because of these efforts, and because dairy 
cattle breeders hav e adopted innovativ e tech- 
nologies through the vears, far more is known 
about reproduction in the cow than in other 
farm animals. The demand for milk and beef 
has provided an impetus for the speedy intro- 
duction of technologies that might prove eco- 
nomically adv antageous. 
Several observations can be made about the 
state of the art for 1(S technologies that enhance 
the inherited ti’aits of animals. (See also app. 
Il-C.) 
The technologies are at different stages of re- 
search and development. 
The practice of ,AI in dairy cattle has had the 
greatest practical impact of all the genetic tech- 
nologies used in the breeding of mammals. In 
contrast, not a single farm animal has been suc- 
cessfully raised after a combination of in vitro 
fertilization and embryo transplant. The use- 
fulness of several of the technologies for animal 
production, such as recombinant DNA (rDNA) 
and nuclear transplantation, is purely specu- 
lative at this writing. 
The usefulness of the technologies differs from 
species to species. 
These differences can often be explained by 
biological factors— e.g., sperm storage capabil- 
ities are currently limited for swine because 
freezing kills so many of the sperm. Manage- 
ment techniques are important as well; exten- 
sive beef-raising systems have in the past made 
estrus detection and synchronization imprac- 
tical, thereby limiting the use of AI. (Fewer than 
5 percent of the U.S. beef herd are artificially in- 
seminated, compared with 60 percent of the na- 
