Protecting Our Genetic Base

Our 19th research edition is rich with new information. It is our hope that this special edition will make management of your hog operations better, more efficient and, eventually, more profitable. We tip our hats to the many university researchers and graduate students in the United States and Canada who have contributed to this effort and we extend our thanks. One very special program that you may

Our 19th research edition is rich with new information.

It is our hope that this special edition will make management of your hog operations better, more efficient and, eventually, more profitable.

We tip our hats to the many university researchers and graduate students in the United States and Canada who have contributed to this effort — and we extend our thanks.

One very special program that you may not be very familiar with is the National Animal Germplasm Program (NGAP) — the livestock and poultry arm of the larger National Center for Genetic Resources Preservation — launched by the target="_new">USDA Agricultural Research Service (ARS) in 1990. The goal of this initiative is to collect and preserve plant and animal germplasm for future research and use in their respective industries.

One simple example will suffice: Did you know that the rootstock on which most U.S. peaches are grown was originally collected in China — in 1898?

Now, pigs and peaches are two completely different things — but imagine if those peach trees had been wiped out by disease. There would be no peach pie, no peach preserves, no peach anything.

Taken a step further, imagine if all but a few trees died — and those few survivors were resistant to the blight?

That's where preservation comes in — and it applies to livestock as well as lima beans.

By the late '90s, NAGP members began assessing animal genetic resources across species. From this assessment, concerns about a narrowing genetic base began to emerge.

Interest in the shrinking genetic base of the swine industry became particularly keen as artificial insemination gained popularity. The need for fewer boars selected with greater selection intensity fueled concerns that some valuable genetic baselines might be lost.

I have always been a strong advocate for preserving as broad a genetic base as possible in the swine industry for the simple reason that we otherwise may never know if that one special line carries the gene(s) for resistance to the PRRS virus or the key to better pork quality, for example.

Therefore, this month's editorial column is part opinion and part progress report from the folks spearheading the swine portion of the NAGP project.

10-Year Progress Report

The swine committee, formed at the inception of the NAGP, has been one of the most active. Representatives from universities, breeding companies and the purebred associations have helped prioritize and develop collection strategies or research projects that address genetic diversity or the preservation and utilization of cryopreserved gametes (mature sperm or egg).

The primary focus of the NGAP preservation effort is to stockpile the germplasm of breeds or industrial lines needed to reconstitute the genetic base should a disease, such as a foot-and-mouth disease outbreak, decimate the national herd. The program also provides a diverse set of genetics that can be accessed to reintroduce genetics — for production or disease-resistant purposes — that otherwise may have been lost. Similarly, the U.S. research community can access the collection to reconstitute or develop new research lines, or as a source of DNA for exploring the pig genome.

In the decade-old program, the swine collection represents 34% of the livestock samples collected, the largest segment in the repository. As of November 2009, there were 1,165 animals represented by semen or embryos and 183,229 total units of germplasm (semen and embryos).

Table 1 lists the 16 swine breeds, represented by 393 boars. In addition, there are 25 industrial or research genetic lines representing 630 boars. These populations are principally composites that have undergone intensive selection by the various U.S. swine breeding companies and research institutions.

Boars are targeted for sampling based on pedigree information maintained by the purebred breed associations. Pedigrees are used to calculate a boar's genetic relationship to other boars in the breed and to boars in the repository. This vetting process helps assure that the breadth of the breed's genetic variability is being captured.

The NAGP Swine Committee's goal is to collect semen from at least 100 boars per breed from different genetic clusters. Key challenges include establishing the genetic diversity within each breed and how the collection can be kept current.

Preservation Process

Research at Purdue University has shown it is critical that semen be maintained at 62.6 °F during transport to the NAGP cryopreservation and storage facility in Fort Collins, CO. When semen samples stray from a relatively narrow temperature and pH range during shipping, the percentage of motile sperm in frozen-thawed semen samples decreases rapidly.

In 2006, Purdue University, Newsham Choice Genetics and NAGP evaluated the post-thaw viability of four composite-line populations. No significant difference between genetic lines was found, but boar-to-boar variation and the source of the semen were important variables. These findings indicate that the cryoprotectants do not have to be modified for different pig populations, and it underscores the importance of semen handling protocols.

While boar-to-boar variation is important, it is not cost effective to change freezing protocols from one boar to the next. Still, knowing the viability of a boar's frozen-thawed semen or the amount of semen cryopreserved, and/or adjusting the number of sperm needed for a single insemination can be made.

Future of Frozen Semen

The use of frozen-thawed semen in the swine industry has been limited due to low fertility rates and reduced litter size. Whether more sperm per insemination could overcome these limitations remains a question. Naturally, NAGP wants to maximize the success rates whenever stored germplasm is used to reconstitute a population.

In a collaboration with the University of Illinois, Purdue University and NAGP, a trial was conducted in which gilts were inseminated either once or twice with one, two or four billion sperm. Results show that the number of sperm and number of inseminations had no impact on pregnancy rate or litter size. These results are encouraging because it indicates that cryopreserved semen can be effectively used and the target quantities of germplasm stored for each breed can be lowered. Still, the number of germplasm collections for most breeds needs to be increased to ensure the breeds can be reconstituted if the need arises.

New and additional efforts are needed to further strengthen the collection of germplasm and better understand the genetic diversity of U.S. swine populations. These efforts will include: 1) Evaluating the genetic diversity of swine populations using DNA markers, as such an effort will help guide collection development; 2) Continuing to improve the post-thaw viability of boar sperm; and 3) Expanding the capacity of the Animal Germplasm Resources Information Network (GRIN) database to incorporate genomic information and phenotypic data of the animals stored in the repository. This will allow researchers to utilize samples in their evaluation of the pig genome.

The NAGP swine committee is grateful to swine owners/breeders, stud managers and staff, and the breed associations for their assistance with the project. The swine committee is chaired by Terry Stewart, Purdue University. For more information, contact NAGP's Harvey Blackburn by phone (970) 495-3268 or e-mail, or visit the NAGP Web site:

Table 1. Swine Germplasm Collection by Breed
Breed Units of Semen Number of Boars % of Goal (18,750)
Berkshire 8,007 30 42.7
Duroc 13,975 51 74.5
Hampshire 7,665 35 40.9
Landrace 8,599 30 45.9
Yorkshire 26,526 92 141.5
Chester White 5,487 20 26.8
Poland China 105 1 0.5
Spotted 1,764 9 9.4
Hereford 4,871 22 26.0
Mulefoot 722 1 3.8
Red Wattle 997 1 5.3
Wessex Saddleback 508 2 2.7
Tamworth 2,193 9 11.7
Fengjing 545 22 10.9*
Meishan 7,061 43 125.0*
Meishan embryos 449 - -
Ming 524 20 10.5*
*The Fengjing, Ming, and portions of the Meishan collection are from the original importation into the United States. No further collection activities are currently planned for these breeds.