Appendix ll-C— Animal Fertilization Technologies: *311 
SI \ll ()l IMh \HT 
Siirijiriil. I’rf^iuiiu \ ralrs ol 51) to 75 [WiTent 
art- arhi«‘\ ahlf m fov\> sfut*[), goats, pigs, and 
hoiM'-* Surgu al transtcr is tin* onlv piMi tical nu*tho<i 
in shi*fp goals anil jiigs and is lh«* pivdoininant 
in«‘thod tor » ov\ s and hoi srs \ nuin()(*r of factors 
d»‘t»*rmini‘ itu* smiTss ot surgical transfer: age and 
(|u.ilit\ of eiiif)r\os >iti* of transfer, ift*grt*t* of s\n- 
chroiu fH'lween eNlroiis cycles of the donor and re- 
(ipients nuinfier of emfiryos transferred in \itro 
culture conditions skill ot jM’rsoniiel. and manage- 
m»*nt l**cfmi(|ues I tie 50- to HO jiercent success rate 
in cattle comjiarf's witfi M sin cess rales at first ser\ • 
iie (I’regnam v rales stiould not fie confused with 
suri \\ al rates hich mav fie mucfi low er I 
Nonsiirgicul. - I his method is an adaptation of 
\l Rejnirted succevs rates are much lower tfian 
those wilfi surgical transfer .\onsurgical transfer is 
not useil in sfi*t*p go.its or pigs 
\l)\ AN I \(;i s 
1 Ofitainmg offspring fmm females unalile to su[i- 
(Mirt pregnanc\ 
2 Ofitaming more offspring from valuafile females. 
3 U ilh a homo/.ygous donor undesirahle riH-essii e 
traits among animals used for \l can he rapidiv 
detivteil 
4 Introducing new genes into s}M*cific pathogen-free 
sw me herds 
5. foupletl with short- or long term emhrvo storage. 
trans()ortation of animals as emfir\(is 
H Increasing the (lopulation fiase of rare or endan- 
geretl breeds of animals hv use of closely related 
breeds for ret'ipienls 
7. Separation of embryonic and maternal influences 
in research 
ms \n\ \ NT AGES 
f. Personnel requirements in surgical transfer ac- 
count for a large share of high costs and thus limit 
applicability in animal agriculture. 
2. Prm ision of suitable recipients is the greatest 
single cost in embryo transfer. 
FI Tl RE 
Surgical transfers will remain the method of 
choice for sheep goats, and pigs in the foreseeable 
future. For cows and horses, however, nonsurgical 
methods will be increasingly used rather than sur- 
gical techniques (and this will be apparent) within 
the ne.xt year or two. It is likely that half of the com- 
mercial transfer pregnancies in cattle in North .Amer- 
ica in 1980 v\ill be done nonsurgically, even if suc- 
cess rates are only 60 to 80 percent of those obtain- 
able with surgical transfer. .Among future appli- 
cations. a role for embryo transfer can be predicted 
in progeny testing of females, obtaining twins in beef 
cows, obtaining jirogeny from prepubertal females, 
and in combination with in \'itro fertilization and a 
\ariety of manipulative treatments (e.g., production 
of identical tw ins, selling, genetic engineering, etc.) 
Embryo storage 
DEFINITION 
•Maintenance ot embryos for several hours or days 
(short-term) or for an indefinite length of time (freez- 
ing). 
STATE OF THE ART 
Short-U?rni.— The requirement for embryos 
from farm animal species has not been defined, 
although adequate culture systems for the short in- 
ter\al between recovery and transfer have been 
developed by trial and error. Whereas the important 
parameters of culture systems have been identified 
(e g., temperature, pll, etc.), optimal conditions have 
not been determined. Cow embryos may be stored 
for three days in the ligated oviduct of the rabbit. 
Long-lemi (I'rtiezing).— No completely adequate 
protocol e.xists for freezing embryos of farm species. 
One-third to two-thirds of embryos are killed using 
present methods. Pregnancy rates of 32 to 50 per- 
cent for cattle, sheep, and goats have been reported 
after freezing. No successful freezing of swine or 
horse embryos followed by development to term has 
been reported. Despite disadvantages (one-half of 
embryos are often killed) advantages are such that in 
some situations embryo freezing, and embryo sell- 
ing. are already profitable. 
ADVANTAGES 
1. .Amplification of advantages of embryo transfer. 
2. Elimination of requirements for large recipient 
herds when embryo transfer is being used. 
3. Reduction of costs in animal transport. 
4. Control of genetic drift in animals over prolonged 
time interx’als. 
FUTURE 
Anticipated development of embryo culture tech- 
nology w'ould be of significance in efforts toward in 
\'itro maturation of gametes, in vitro fertilization, sex 
determination, cloning, and genetic engineering, all 
of which involve prolonged manipulation of gametes 
and embryos outside of the reproductive tract. 
As freezing rates improve, nearly all embryos re- 
covered from cattle in North America will be frozen. 
Probably as many as half of the embryos will be 
deep-frozen for 2 to 3 years. It is unlikely that suc- 
cess rates will ever approach 90 percent of those 
