Ch. 9— Advances in Reproductive Biology and Their Effects on Animal Improvement • 185 
in^ animals wilh littln rn^ard lor g(MuMic poU’ii- 
tial. 
Kmhi'u) transtor ma\ pay tor ilsell in 
ItM'iiis ol milk proiluc'tion ot tht* animals pro- 
(liK'tnl exc'opt iiulirorlK through hulls. Kalhor, it 
is used mostly to produce outstanding row s tor 
sale. Other eommereial a{)pIieations tor eattle 
inelude ohtaining progein trom otherwise in- 
tei'tile rows, exporting t'liihi xos instead of ani- 
mals. and tt'sting toi’ reeessi\ (‘ genetic traits. 
Kmhryo transfer progeny must he worth 
each to justity tlu> costs and risks, .\hout 
SI. 500 of this represiMits costs due to emhrxo 
transfer and SI. 000 the costs of proilucing 
cakes normally. If genetic gain from emhryo 
transfer comes onl\ from dam paths, the e.\- 
[)ected gain ox er M alone is 70 Ih \ r. K.xtra gain 
at SO. 05 II) ahox e feed cost would hax e to ac- 
cumulate for 79 years before added gain w ould 
equal exen a S300 embryo transfer cost per 
[)iegnancx. If less semen is neetled lalloxxing 
more intensix e hull selection), the e.\j)ected gain 
of 129 Ihyr must accumulate for 40 years to 
balance an emhiyo transfer cost of S300 per 
pregnancy. 
Emhrxo transfer and perfect se.xing of semen 
XX ould combine to im[)i ox e genetic gain (in milk 
production) slightlx. The use of less semen 
might be possible through application of in x itro 
fertilization. Hoxxexer, feasibility based on 
genetic gain xxould still require holding all costs 
doxx n to around S50 to S90 per conception. The 
general conclusion is that costs of emhi yo trans- 
fer must he greatly reduced to he economically 
feasible if only genetic gain is considered. 
Estrus Synchronization.— The ax ailability 
of an effectixe estrus synchronization method 
XX ould prox ide strong impetus for increased use 
of .AI and embryo transfer in dairy cattle. The 
detection of estrus is an e.xpensix e operation; ef- 
fectix e control of estrus cycling also requires in- 
tensixe management, adequate handling facil- 
ities, and close cooperation betxxeen the pro- 
ducer, x eterinarian, and .AI technician. 
Summary.— 
• Proper application of progeny testing xvith 
selection and AI can increase the genetic 
gain for milk yield more than Ixxo times 
fast(M' than is occurring today. Improxed 
exaluation of coxxs, pro|)er economic em- 
phasis on other traits, and strict adherence 
to .seUu’tion stanilards are the keys. Bio- 
logical limitations to this rate of genetic im- 
proxement cannot he anticipated in the 
foreseeable future. 
• AI of dairy cattle, xxith the present intensi- 
ty of sire .selection, should increase the net 
xxorth or |)rofit of animals (increased x'alue 
minus extra costs of the -A I pi'ogram) about 
SlO.OO head per year. By 1990, « million 
daily coxxs in ,AI programs xxould he xxorth 
about S800 million (8 X i()« X $i() X 10 
years) more at current market pi'ices as a 
result of continued u.se of AI. 
• Se.xing of semen xxhen used xxith A I may 
pax for it.self if the cost per breeding unit 
can h(' kept biMxx een $10 and $20. 
• Emhryo transfer is unlikely to pay for itself 
genetically unless the cost is reduced to be- 
txxeen $50 and $90 i)er conception. Hoxv- 
ex er, des|)ite its high costs, it is used to pro- 
duce animals of e.xceplionally high x^alue. 
(See app. ll-(] for an exjtlanation of reasons 
other than genetics xvhy embryo transfer is 
used.) 
• Estrus synchronization is noxx' ax ailable for 
use xxith heifers, and should increase the 
use of ,AI and consequently the genetic im- 
prox ement of dairy cattle. 
• ,A secondary benefit of all technologies is 
the increased number of skilled persons 
xx ho can prox ide technical skills as well as 
educate dairymen in all areas. Also, a 
unique pool of reproductive and genetic 
data has been accumulated. 
BEEF CATTLE 
There is no single trait of overriding im- 
portance (like milk production in dairy cows) to 
emphasize in the genetic improvement of beef 
cattle, the rate of growth is a possibility.* It is 
also difficult to select for several traits at once, 
'Beef and dairy cattle are usually different breeds in the United 
States. In the literature and in research they are often referred to 
as different species. In other countries, notably in VX’estern Europe 
and in Japan, so-called "dual purpose" cattle are used to produce 
both beef and milk. In the United States, old dairy cows usually be- 
come hamburger. 
