Avian Genetic Stock Preservation: An Industry Perspective 1

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1 Avian Genetic Stock Preservation: An Industry Perspective 1 J. E. Fulton 2 Hy-Line International, Dallas Center, IA ABSTRACT There are different types of poultry genetic sperm. Thus, the W chromosome and the mitochondria, resources including mutants, inbred lines, specialized/ selected stocks, standard breeds, and elite commercial pure lines. These resources differ in their degree of value to the poultry industry. There is considerable concern within poultry breeding companies about the continuing losses of these genetic resources, particularly as this loss seems to have escalated over the past decade. Varied genetic stocks can provide fundamental information regarding gene function, genetic interactions, and genetic pathways. This information is important for efficient improvement of commercial poultry performance. Equally important is the role of these genetic resources in teaching and the education of students and future researchers. Currently, the only practical preservation method for birds in the poultry industry involves live bird conservation. Flocks of elite commercial stocks are maintained at multiple locations, providing insurance against disease outbreak and the possibility of quarantine restrictions. The current cryopreservation methods apply only to which are contributed by the female gamete, cannot be preserved. Cryopreserved semen shows considerable variation in both fertility and hatchability rates, not only among lines, but also among males within lines. The biological basis for this variation is unknown, and there is concern that the use of cryopreserved semen may result in unintended selection and loss of genetic variability. Cryopreservation cannot be applied in the poultry breeding industry until methodologies are developed that produce high viability for both male and female avian preserved gametes. More research is needed in the areas of sources of variation in viability following freeze/thaw, female gamete cryopreservation, and embryo preservation. Because there are currently no appropriate methods of cryopreservation available to the poultry industry, the long-term preservation of commercial elite stocks must continue to rely on live bird conservation. Because of the high costs of this live bird preservation, stocks with no perceived current economic value will not be maintained. Key words: genetic resources, cryopreservation, industry perspective 2006 Poultry Science 85: INTRODUCTION Over the past 3 decades, a considerable portion of avian genetic stocks has disappeared (Pisenti et al., 1999; Fulton and Delany, 2003). The poultry breeding industry is concerned about the loss of the reservoir of genetic variability. The current status of preservation, which must utilize live animal stocks, has contributed to the loss of genetic resources. Future preservation utilizing gamete or embryo cryopreservation will be done once appropriate technologies are developed. The comments in this article are primarily from the perspective of the author from within the egg-layer breeding industry, although the author did have discussions 2006 Poultry Science Association, Inc. Received September 12, Accepted September 20, Paper for the Poultry Science Association Ancillary Scientists Symposium, July 31, 2005, Auburn, Alabama, Conservation of Avian Genetic Resources: Current Opportunities and Challenges, organized and chaired by Dr. Muquarrab Qureshi. 2 Corresponding author: jfulton@hyline.com with geneticists from within the broiler breeding industry. The majority of these comments apply specifically to chickens. The status of the genetic resources for other avian species, such as turkeys, ducks, geese, and quail, is not covered in this article. However, the problems and issues outlined here are considerably amplified for these other avian species, as there are even fewer genetic resources available and the development of methods for preservation is behind the current application levels for the chicken. TYPES OF GENETIC RESOURCES The poultry genetic stocks can be divided into 4 categories: the mutant stocks, inbred lines and specialized or selected strains, standard breeds, and elite commercial pure lines. These different resources each have different value to the industry, but all have an important function. MUTANT STOCKS The mutant stocks include the numerous single-gene phenotypic variants such as polydactyly, creeper, and 227

2 228 FULTON restricted ovulator. These mutants are mostly held at public institutions, although some of these mutant phenotypes are also found within specific breeds in the hands of poultry fanciers (e.g., henny feathering in the Sebright and Campine breeds; polydactyly in Dorking and Houdan, ptilopody in Cochin and Sultan). Historically, a few of these mutants have been utilized for commercial poultry production. The naked neck gene is utilized by some breeders to produce birds with better heat tolerance. The barring gene from the barred Plymouth Rock has been used in the past for 1-d-old chick sexing, but is not in common use today. Commercial broilers utilize dominant white to produce non-pigmented birds. The dwarfism gene was used in the broiler industry to provide more efficient parent stock. Today, color sexing of the commercial brown egg-producing stocks utilizes the gold and silver alleles at the sex-linked silver locus. The sex-linked feathering rate gene is used extensively for rapid determination of sex in 1-d-old commercial white egg-laying stocks. This mutation probably did not originate within the White Leghorn breed used for commercial white egg production, but was probably crossed in from one of the other breeds. Are these mutant stocks of value to the industry today? Those genes of greatest commercial value have probably already been utilized by the commercial production industry. However, these mutants do have further intrinsic value. It is only by understanding the genetic causes of phenotypic variation that we can really understand how genes function. Understanding the underlying causes in different pigmentation genes (Kerje et al., 2004) allows DNA tests to be developed that can then be used to remove low levels of pigmentation-producing alleles in broiler stocks that can cause occasional undesirable pigmentation in carcasses. Understanding the underlying genetic causes of slow feathering (Bacon et al., 1988) explained the low level of revertants observed in all slowfeathering stocks and allowed for the development of a DNA test to identify carriers (Okimoto, 1998). These mutant stocks are also a source of entry-level interest in genetics, as they are ideal teaching tools. Industry is having an increasingly difficult time finding recent graduates with knowledge in poultry genetics. There are fewer students with poultry experience, which is, in part, related to fewer poultry resources. Recent industry hires are coming from dairy or swine genetics background. SPECIALIZED STRAINS The specialized strains have been developed at public institutions as research tools to understand various biological phenomenona. Many of these stocks were developed over the lifetime of a researcher, requiring multiple generations of phenotypic selection (Abplanalp, 1992) org/chantecler.htm; These lines cannot be regenerated. In many cases, the initial genetic resources that were used no longer exist; in addition, long-term research support is no longer available. Inbred lines were developed at numerous locations to gain understanding of inbreeding depression and to replicate the successful gains made in subsequent outcrossing as observed for commercial plant breeding. The development of inbred lines is very labor intensive, with a high attrition rate of lines within the first few generations. All commercial breeding stocks today utilize heterosis by crossing different strains. Congenic lines have been developed to identify genes involved in disease resistance (Bacon et al., 2000). Stocks with differences in various virus receptors allow the specific-pathogen-free breeding industry to isolate and identify specific virus strains. Recently, specialized strains have been used in QTL mapping, including genes of economic importance. The information from this type of research has been integrated into commercial breeding programs. STANDARD BREEDS The standard breeds include all of the breeds recognized by the various breed associations throughout the world. Some of these breeds trace back several centuries and to specific regions of the world [e.g., Phoenix and Shamos from Japan, Aseel from India, Campine from Belgium, Sultans from Turkey (American Poultry Association, 2001)]. The crested Paduan or Polish chicken is described by Aldrovandi in 1600 (Lind, 1963 translator). Some of the newer breeds were developed by poultry fanciers (e.g., Sebright bantams by Sir John Sebright in the UK, Buckeye by Nettie Metcalf in Ohio). The Chantecler was developed in Canada to provide a bird that was better able to survive harsh Canadian winter conditions. The Holland breed was developed by Rutgers Breeding Farm to produce a dual-purpose bird that laid white-shelled eggs. 3 The standard breeds are the source of all existing commercial stocks. All commercial white egg lines are from line crosses involving the White Leghorn breed. Commercial brown eggs are produced from a breed cross utilizing the Rhode Island Red breed and a synthetic White Plymouth Rock. The modern commercial broiler stocks were developed from crosses utilizing Cornish and White Plymouth Rock breeds. Thus, all commercial production birds of today derive from very few of the standard breeds. Has all of the commercially useful genetic material been gathered from these breeds? The answer is unknown. No commercial breeding company has an infallible crystal ball. Breeding companies respond to the needs of their customers. Future requirements are unknown. Are the commercial breeding companies concerned about the loss of these resources? Yes, if these resources are gone, then they can never be utilized. As company mergers occur in the commercial breeding industry, cost-cutting measures mean that lines are eliminated. Today, independent sources of new germplasm are very scarce.

3 ANCILLARY SCIENTISTS SYMPOSIUM 229 PRESERVATION OF GERMPLASM Live Animal Preservation Currently, all commercial breeders use live animal reserves as their method of preservation of elite commercial stocks. These are additional birds of the pedigreed pure lines that are housed in different geographical locations. These duplicated stocks actually serve 2 different purposes. Biological Security. Protection of the elite commercial lines against various natural disasters is of great concern. Housing of pedigree lines at remote locations is security against losses caused by fire, tornado, or other physical disaster. Also, disease outbreaks can kill or reproductively damage valuable breeding stocks. Multiple locations are insurance against these types of losses. Economic Security. This has become a very important issue within the past 3 yr. Outbreaks of disease, such as avian influenza, exotic Newcastle Disease, and lymphoid leucosis have resulted in importation restriction for hatching eggs or chicks by some countries. These embargoes are frequently politically based, as disease-affected flocks may be hundreds of miles away from the source of the hatching eggs or chicks to be exported. These embargoes can completely halt the export of breeding stock, effectively closing down all international business. The embargo boundaries are politically defined. Thus, these additional flocks must be located in different countries. Cryopreservation Germplasm cryopreservation would be a very valuable tool for the poultry industry as well as for the successful preservation of the poultry genetic resources that still exist. Lines not in use today by the industry could be stored via cryopreservation and regenerated as needed in the future. The current generation of elite line breeding stock could be stored as protection against natural disasters and insurance against inbreeding and inadvertent changes in breeding direction. In addition, cryopreservation would allow the inexpensive maintenance of control strains useful for accurately measuring genetic progress over time. Consistent and reliable semen storage would be helpful for keeping genetic potential from additional males, for measuring of trait improvement through progeny testing, for transporting frozen semen, and for the ability to quickly apply improved male genetics worldwide. Semen Preservation. The current state of cryopreservation technology for poultry is inadequate for use by the commercial poultry breeding industry. The fertility rates of cryopreserved semen are very low, generally <30%. This rate is very line dependent, with some lines providing 0% fertility. Causes of this variability are unknown, and there is concern within the industry that utilization of only those lines with successful cryopreservation will result in inadvertent selection of other undesirable traits. In addition, there is considerable within-line variation in fertility rates following cryopreservation. Most cryopreservation studies with poultry semen are done using pooled semen. It is known that not all males contribute equally in progeny from pooled semen (Birkhead et al., 1999; Donaghue et al., 2003). The underlying genetic causes of differences in male fertility are not known. There is concern that the use of cryopreserved semen could result in an increase in inbreeding, as not all birds genetic contribution could be preserved. There are probably numerous genetic causes as well as environmental factors (including diet and age) that influence success rates of fertilization following cryopreservation. More information is needed on these factors before cryopreservation can be successfully utilized by the commercial poultry breeding industry. Female Gamete Preservation. Currently, there is no way to preserve the female avian gamete. The large yolky egg is not amenable to current cryopreservation methods. This is a very serious issue for line preservation, as a line cannot be preserved without both the male and female contributions. Lack of the female gamete means that not only are we missing one entire chromosome (W chromosome is in females only), but also the entire mitochondrial genome. Whole Embryo Preservation. There is some exploratory work being done on the cryopreservation of primordial germ cells. These cells can be used to reconstitute gonadal tissues with germ cells from a donor line. Currently, this technique provides very low yields of chimeric chicks with reconstituted gonads and very low levels of subsequent donor gametes. This method is not useable at this time for whole embryo preservation (Petitte, 2005). RESPONSIBILITY Who should be responsible for the preservation of poultry genetic resources? Four different groups have been proposed as the appropriate venues for preservation. Poultry Fanciers These are the breed societies and organizations that are organized around the poultry fancier exhibition shows. Birds are kept for exhibition purposes or for small-scale farm flocks and selected primarily for phenotype. There are only a small number of breeders who provide chicks to fanciers. Flock numbers are small and under considerable flux as people move in and out of the hobby. Disease control is minimal. Not all breeds are well represented, and many breeds are in constant danger of being lost. We do not house the Library of Congress in the basements of private homes. Neither should we place our genetic variation in the backyards of private homes. Industry It has been suggested that industry should be maintaining poultry genetic resources, as industry has gained

4 230 FULTON the most from the use of this variation, and they can afford to maintain it. However, the poultry breeding industry consists of a very small number of highly competitive companies. They have very tight financial responsibilities. Lines not performing at required economic levels will be eliminated. Every merger between breeding companies results in elimination of lines with lesser economic efficiency. Industry is not the location for preservation of genetic variation of limited value today, but with potential value tomorrow. Land Grant Universities Most of the remaining genetic resources are at Land- Grant universities. Historically, this has been where the special lines have been developed and maintained. This is where these resources have been used most effectively as teaching and research tools. However, the role of the Land-Grant universities has changed over the past few decades. Most of their physical facilities for animal housing have not been updated, meaning that biosecurity of the few remaining facilities is woefully inadequate. There are insufficient funds and other resources to maintain the genetic resources at the Land-Grant institutions. The proposal in the President s 2005 budget to eliminate experimental station research funds is another sign of this change. Passage of this bill will eliminate the few remaining genetic resources at Land-Grant institutions. Government The most logical source of support is government. The consumer has benefited the most from the historical use of genetic resources. Today, chicken meat and eggs are a very inexpensive source of high quality protein. The success of the poultry industry has been based on the use of appropriate genetic foundation stocks, the application of heterosis, and the use of improved breeding techniques. Only a governmental agency can provide the long-term view and stable support needed to preserve the existing avian genetic resources. The National Animal Germplasm Program (NAGP) was developed within the USDA to fulfill a congressional mandate of animal germplasm preservation within the US. This program is responsible for animal germplasm for all agriculturally important animal species, including cattle, goats, sheep, swine, chickens, turkeys, geese, and ducks as well as numerous aquatic species. This program is currently funded with $850,000/yr. The NAGP exists currently as a repository for cryopreserved gametes and embryos. The low level of funding does not allow for any other aspects of germplasm preservation. Because cryopreservation is not a current option for the preservation of poultry germplasm, the NAGP does not fulfill the germplasm preservation needs for avian species. Either the NAGP funding needs to expand to include live animal preservation or some other means of national support needs to be provided. The avian genetic resources described here have considerable value outside of the realm of agriculture. There are many examples of avian species used as model organisms for biomedical research (Fulton and Delany, 2003). It seems appropriate that these genetic resources should be supported through funding sources not exclusively from USDA. In addition, research funds need to be made available to improve cryopreservation methods for all avian species. This research is crucial to the agricultural community for those avian species utilized for human food production. This research is also of importance to the zoological community for conservation and preservation of other avian species. Numerous endangered bird species could benefit greatly from improved understanding of the issues involving sperm development and cryopreservation of both male and female gametes. CONCLUSIONS There is concern that new avian genetic resources are not being developed because of lack of long term-commitment in planning, funding, or physical facilities. Disease pathogens change over time, becoming increasingly more virulent. Metabolic challenges change as production demands fluctuate. With no new resources being developed, it is becoming increasingly difficult to answer the questions that arise with today s genetic stocks. With few historical resources remaining, it is becoming increasingly difficult to determine if new problems are arising because of changes in environment or genetics. The resources need to be available to answer production questions that arise in today s modern production systems. An adequate preservation program, utilizing both live birds and cryopreservation, needs to be developed. This will aid considerably in the maintenance of existing genetic stocks, minimize further losses of genetic diversity, and encourage continued resource development for understanding the challenges of the modern commercial chicken. REFERENCES Abplanalp, H Inbred lines as genetic resources of chickens. Poult. Sci. Rev. 4: American Poultry Association American Standard of Perfection. Am. Poult. Assoc., Mendon, MA. Bacon, L. D., H. D. Hunt, and H. H. Cheng A review of the development of chicken lines to resolve genes determining resistance to diseases. Poult. Sci. 79: Bacon, L. D., E. Smith, L. B. Crittenden, and G. B. Havenstein Association of the slow feathering gene (K) and an endogenous viral (ev21) gene on the Z chromosome of chickens. Poult. Sci. 67: Birkhead, T. R., J. G. Martinez, T. Burke, and D. P. Froman Sperm mobility determined the outcome of sperm competition in the domestic fowl. Proc. Biol. Sci. 2666(1430): Donoghue, A. M., J. D. Kirby, D. P. Froman, S. P. Lerner, A. N. Crouch, L. M. King, D. J. Donoghue, and T. S. Sonstegard Field testing the influence of sperm competition based on sperm mobility in breeder turkey toms. Br. Poult. Sci. 44: Fulton, J. E., and M. E. Delany Poultry genetic resources Operation rescue needed. Science 300:

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