Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
2/28/01
Contacts:
Curt Youngs, Animal Sciences, (515) 294-5541, cryoungs@iastate.edu
Elaine Edwards, Continuing Education and Communication
Services, (515) 294-5168, eedwards@iastate.edu
ISU Professor Examines Future of Cattle Breeding
OTTUMWA, Iowa -- Despite the myriad of forces that will change the usual way of doing business for beef producers, a few technologies are certain to play an important role in the future of cattle breeding programs. Curt Youngs, associate professor of animal science, Iowa State University, outlined these technologies and the future of cattle breeding at the 2001 Cornbelt Cow-Calf Conference.
"Three of these technologies are predetermining the sex of offspring, using genetic markers in selection systems and propagating genetically elite animals via nuclear transfer, most commonly referred to as cloning," Youngs said.
Sex of offspring
There are three methods for predetermining the sex of
offspring at birth. One method is ultrasound generally used
at day 60 of gestation. With 98 percent accuracy, many
veterinary clinics offer this service to their clients.
However, a drawback to fetal sexing is that producers have
to decide whether or not to terminate the pregnancy if a
fetus is the undesired sex, Youngs said.
A second option is embryo sexing. "By determining the sex of an embryo prior to its transfer to a recipient female, it is possible to avoid the major objection to fetal sexing because only embryos that will produce the desired sex will be used to establish pregnancies," Youngs said. However, approximately 50 percent of embryos will still be the undesired sex.
The third method, sperm sexing, offers the advantage of minimizing production of offspring of the undesired sex. Sperm sexing technology using a flow cytometer was developed at the U.S. Department of Agriculture research center in Beltsville, Md. "Sexed sperm will soon be available to cattle producers; however, the cost of sexed semen and its cost effectiveness in the beef cattle industry remains to be decided," Youngs said. In addition, other techniques are being developed to segregate sperm possessing an X versus Y chromosone, including the use of antibodies or timing of artificial insemination.
Genetic markers
"In an ideal world, cattle producers would select their
breeding stock based on an animal's genotype," Youngs said.
"However, because the cattle genome has not yet been
completely sequenced, producers cannot select animals based
on their genotype but instead must select animals on an
estimate of their genetic worth."
Youngs said one of the uses of molecular genetic information will be marker assisted selection. "As a part of the cattle gene mapping project, known sequences of DNA dispersed across all 60 chromosomes have been identified. Many of these DNA sequences, called genetic markers, are known to vary from animal to animal and are called polymorphic," Youngs said.
Geneticists are examining the relationship between these DNA polymorphisms and animal performance, with the hopes of identifying certain genetic markers associated with enhanced animal performance.
"Although it would be wonderful to identify the genes that impact traits such as tenderness or marbling, it may not actually be necessary. Some of the genetic markers may be located so close to genes of economic importance that the genetic markers and the gene of interest are inherited in a package deal," Youngs said. "These relationships are known to be a cause of genetic correlations among traits, and in the future it will be possible to select animals based on favorable linkage combinations if the animal's genotype is known."
Youngs said molecular genetics also makes it possible to verify parentage. In the future, breed associations may require parentage verification before offspring may be registered, he said.
Nuclear transfer
One advance in cell biology in the past five years is
somatic cell nuclear transfer, otherwise known as cloning,
which involves the transfer of a compete set of chromosomes
from one cell to a different cell whose chromosomes have
been removed.
In 1997, the world was shocked by the announcement from researchers in Scotland concerning the creation of Dolly, the world's first nuclear transfer offspring produced by using a cell taken from an adult animal as the donor cell. "This breakthrough opened a whole new gamut of possibilities for livestock breeding," Youngs said.
"With somatic cell nuclear transfer, cells from an adult of proven genetic merit may be used as the donor cells," he said.
"In the future, it will be possible to knock-out certain genes which are known to be harmful and to insert, at specific sites in specific chromosomes, genes to enhance an animal's structure or function.
Youngs spoke to cow-calf producers and trade industry representatives at the 30th annual Cornbelt Cow-Calf Conference held in Ottumwa Feb. 24. For more information on the conference, contact Byron Leu, ISU Extension beef field specialist, (641) 472-4166.
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