...From the pages of Agricultural Research magazine
Revolutionizing Turkey Production:
Consumers give many thanks for the estimated 5.6 billion pounds of
turkey brought to market each year. U.S. farmers meet that demand by
producing close to 300 million turkeys annually.
For decades, turkey breeders have produced bigger, meatier birds by
using advanced genetic selection. The resulting difference in size between
males, or toms, and females, or hens, requires producers to rely solely
on artificial insemination for reproduction. It's a labor-intensive
and tricky process.
Because an average turkey farm has about 33,000 sexually mature hens to inseminate, scientific advancements are in demand.
Scientists at the ARS Biotechnology and Germplasm Laboratory in Beltsville, Maryland, are using functional genomics to improve reproductive methods used by turkey farmers. Functional genomics is the study of the function of genes in a particular cell and how these gene functions adjust within the cell under changing conditions.
At the Biotechnology and
Germplasm Laboratory in
physiologists Julie Long
and Kurt Zuelke evaluate
whether turkey sperm are
alive or dead in studies
to improve the lifespan
of stored turkey sperm.
|The researchers are focusing on
differences in gene expression within cells in a special site inside the
hen's reproductive tract, called the oviductal sperm-storage tubules (SSTs).
Turkey hens are able to store and keep sperm alive in their SSTs for
up to 75 days. But sperm collected for artificial inseminationthrough
a process called "milking"can stay alive for only 8
to 10 hours outside SSTs. And that's after they're protected in vials
and buoyed by a mixture of nutrients and other fluids called "extenders."
Such a narrow window of opportunity in which to use or lose the sperm poses difficult time limits for farmers.
A SAGE Approach
The researchers are delving into the mystery of how sperm stay healthy for so long inside a hen's reproductive tract. This information could help improve the capability of keeping sperm alive outside the SSTs after milking.
Physiologist Kurt Zuelke (left)
and biologist Wes Garrett select
turkey sperm storage tubule
proteins from a two-dimensional
gel for analysis by mass
spectrometry as a followup
to SAGE analysis.
| Several years ago, while attending
a seminar, reproductive physiologist Kurt A. Zuelke, who heads the Beltsville
lab, heard about a new, computerized, digital method for practicing functional
genomics. It's called SAGE (Serial Analysis of Gene Expression), and Zuelke
has since found it to be spectacularly effective for researching livestock
"In terms of today's genetics research, functional genomics is
where the rubber meets the road," says Zuelke. His team is using
SAGE to study alterations in gene expression when turkey sperm are present
Expressed genes are those genes that are "switched on"that
is, making important proteinsat a given time. Using the SAGE method,
the researchers can count the number of RNA transcripts, or copies,
made by expressed genes. Many transcripts signal high expression; few
transcripts suggest low expression.
"The beauty of SAGE is that it counts close to exactly the number of transcripts of every expressed gene in the entire turkey genome at a particular moment by using digital technology," says Zuelke. "If you have 20 transcripts, then in theory you have 20 SAGE tags."
Improving Sperm Preservation
To maintain a fertility rate of 90 percent or more on turkey farms,
each hen is inseminated once a weekwith about 200 to 300 million
sperm each timefor 5 months. Each collected dose of turkey semen
yields about 9 billion to 12 billion sperm per milliliter.
"Lengthening the time that these sperm stay alive outside the
tom would translate into significant savings for the commercial turkey
industry," says Zuelke.
The first breakthrough study was conducted by Zuelke, reproductive
physiologist Julie Long, and ARS researchers at the Bovine Functional
Genomics Laboratory, also in Beltsville.
The scientists ran two SAGE analyses-one on tissue taken from
turkey SSTs when sperm were present and one when sperm were not present.
They reported that more than 214 genes were expressed at different levels
within SSTs when sperm were present compared to when sperm were not
This was the first report in scientific literature that indicated that
the presence or absence of sperm in the reproductive tract could affect
gene expression within the SSTs. The breakthrough lays a foundation
for understanding which proteins are produced from the expressed genes.
"SAGE technology allows us to study thousands of genes simultaneously,
measure their expression, and quickly identify genetic differences between
cells in the presence and absence of sperm," says Zuelke.
During the study, the team found a particular gene, named "avidin,"
which corresponded to a SAGE tag. Avidin had already been identified
and well studied in chickens. Since the SAGE technique had never been
used in poultry before, avidin was chosen to help validate SAGE in turkeys.
"Now that we have the avidin gene, we can use it as a model for
analyzing other genes expressed in the presence of sperm," he says.
Learning which genes are switched on when sperm are present in the SSTs can help identify which proteins are produced under those special circumstances. Those proteins could then be put into extenders to help prolong the life of sperm outside the SSTs.
The scientists consider the milestone of identifying key expressed
genes as opening a door to further research. They hope that their discoveries
will lead to further knowledge that will eventually allow them to freeze
"If we could extend their survival rate to 24 hours, allowing
them to stay viable overnight, that would open wider transportation
and storage options for better reproductive management," says Zuelke.
The newly developed turkey SAGE tag data has been donated to a database
called SAGE-Map, which is maintained by the National Center for Biotechnology
Information, part of the National Institutes of Health, in Bethesda,
Maryland. SAGE-Map is available to both public and private scientists
for further research and can be accessed at www.ncbi.nih.gov.By
Rosalie Marion Bliss,
Agricultural Research Service Information Staff.
This research is part of Food Animal Production, an ARS National
Program (#101) described on the World Wide Web at www.nps.ars.usda.gov.
"Revolutionizing Turkey Production: Functional genomics is the driving force" was published in the September 2004 issue of Agricultural Research magazine.