Ch. 9 — Advances in Reproductive Biology and Their Effects on Animal Improvement • 187 
It has piviliftfil tlial tlu> a\ ailahility ot 
prosta^laiuliii a^'ents tor regulating estrus eoulcl 
increase tlie numlier ol heel eal\es horn trom 
superior hulls hy ID times, and that perhaps 20 
[lereent ol the I S. heel eow herd coukl reeei\ e 
at least one insemination aiiilii ally hy 1090.-' It 
this lead to a ">0-lh inerease in weight tor 10 [)er- 
eent ot the (\il\t*s hoi'ii. it shoulil ht* worth SI 14 
million to St 22 million each \ear. assuming 80 
or 8a [lereent net call ei’op and SOO per hun- 
ilreilw eight 
The implementation of reeiMith ilexeloped 
estrus s\ nehronization teehnologx might in- 
ereast' the numht*r ot heel eow s hred artit'ieially 
In 4,000.t)00 in the I'nitetl States. Such a pro- 
gram shoulil he sueeesstui in athaneing the 
caking date In one week (hy decreasing the 
cak ing interx all. and in increasing the i|uality of 
the cak es produced. These new cak es could he 
vvoi'th about SI 00 million annually, less about 
SaO million ilue to e.vtra costs associated with 
the s\ nehronization j)rogram. 
Sex Control. — Se.\ control would have a 
dramatic effect on the beef industry. In 1971, it 
was projected that In 1980 sex control could 
ha\ e an annual potential benefit of S200 million 
based on 10 million female cakes being re- 
placed In male calves produced through the 
sexing of semen.-- .At the time of the prediction, 
the market \ alue for steers was about S20 more 
than for heifers. (Steers w ean hea\ ier and gain 
more efficiently.) Now the margin is much 
greater— approximately S50. This potential 
method of biological control is more attractixe 
than the use of additixes like steroids or im- 
plants because of the possible hazards associ- 
ated XX ith them that preclude their use. 
Embryo Transfer. — The possibilities for 
genetic improxement in beef cattle using em- 
bryo transfer haxe been analyzed. It appears 
that embryo transfer programs can be dexel- 
oped to increase the rate of genetic progress for 
-'H. D. Hal's. "Potential Impact of Prostaglandin on Prospects for 
food From Dairy Cattle." Proc. Luialyse Symposium, J. XX'. Lauder- 
dale and J. H. Sokolowski leds.) (Kalamazoo. Mich.: Upjohn, 1979), 
pp. 9-14. 
“R H. Foote and P. Miller. XX hat Might Se.x Ratio Control Mean 
in the .Animal XX orld." Symposium, Am. Soc. of Animal Science, 
1971. pp. 1-10. 
groxx th rate: but the programs are much too ex- 
pensixe to he used oxer the entire population. 
One problem is that the economic xalue of the 
product of a beef coxx is around 2o percent (or 
exen less) of that of a dairy coxx'. Nexei'theless, 
in populations in xxhich ,\l is usetl, embryo 
transfer xxas found to he useful for obtaining 
more hulls from (op coxvs. The females pro- 
duced hy emhi’xo transfer xxould he xxorth mar- 
ginally more than females produced conxen- 
tionally, hut the costs and influence of males 
could spread oxer the population through the 
use of AT The extent of this use of embryo 
transfer xxould be xery small; only a fexv hun- 
dred hulls xxoultl he produced per year for x ery 
large populations, and oxer 99 percent of the 
population xvould reproduce conxentionally. 
Iloxxexer, such programs could haxe consider- 
able economic benefit. Ciive. must be taken to 
minimize increased inbreeding of the popula- 
tion XX ith such a breeding scheme. 
Su miliary.— 
• A1 could substantially improx e economical- 
ly important traits in beef herds. Hoxvever, 
because of the dixersitv of traits consid- 
ered important by different breed groups 
and tbe lack of a national beef testing and 
recording system comparable to NCDHIP, 
economic estimates of its value have not 
been dex eloped. 
• A sexing technology to produce mostly 
males (they groxv faster than heifers) could 
be of enormous potential benefit to the 
beef industry. Hoxvever, no successful 
technique yet exists. 
• Estrus cycle regulation could lead to a sub- 
stantial increase in the number of beef cat- 
tle in A1 programs. The net benefit of this 
technology, coupled with AI, may be as 
high as S50 million per year. Similarly, the 
availability of reliable progeny records 
xvould add to the beneficial impact of AI in 
beef and xvould probably contribute sig- 
nificantly to its use in beef cattle. 
OTHER SPECIES 
Swine. — Much progress has been made in 
improving the overall biological efficiency of 
pork production in the United States. Improved 
