2010 Annual Report
Combining and analyzing sheep DNA from Brazil and the US. Understanding the genetic distinctness of US sheep breeds in relation to those in other countries can impact conservation strategies and breeding programs. Using genotypes generated in our respective countries, ARS scientists at the National Animal Germplasm Program in Fort Collins, Colorado and Brazilian scientists explored methods to combine and analyze genetic differences of sheep breeds found in the US and Brazil. The approach used to merge the data was successful and we were able to determine genetic distances and show how breeds were grouped together based upon physiological function (meat vs wool/hair production). Importantly this study showed that the Brazilian and US hair breeds are substantially different from one another suggesting different countries of origin. As a result, US breeders interested in Brazilian breeds (and vice versa) could expect substantial hybrid vigor by importing and crossing these breeds; and that countries can leverage information generated independently and use that information in their conservation programs.
Securing Holstein germplasm - Collections in France, The Netherlands, and US. Globally, Holstein is the predominant dairy cattle breed and has been shown to have a small effective population size (< 36 animals). Therefore the three countries wanted to know how well Holstein is secured and the diversity represented in the three countries’ gene banks. Working with scientists from France and the Netherlands an ARS scientist provided information on the US Holstein collection, suggested analytical approaches, interpreted the results, and co-authored a proceedings paper. This project indicated that among the three gene banks the US collection was the largest in terms of number of bulls represented, and had the lowest genetic relationships when compared to the French and Dutch collections. Using the effective number of founders to compare gene bank collections to each country’s set of active bulls it was determined that the US collection with 784 founders, exceeding our current population of active bulls with 115 founders. Given these results, we can state that the US collection is the largest and most diverse collection among the three countries. In addition, the US collection is more diverse than the current breeding population of US Holsteins and therefore the gene bank has secured the Holstein breed in the event of a disaster or need to reintroduce genetic variation.
Efficient Use of Cryopreserved Boar Semen. Germplasm collected and stored in a gene bank will become a limited resource as it is used over time. Therefore, optimizing the number of motile cells to inseminate in a sow is important. To address this issue, an experiment evaluating the optimal insemination dose (1.0, 0.75, 0.5, and 0.25 billion sperm) for boar semen was performed. Scientists with National Animal Germplasm Program, in Fort Collins, co-designed, cryopreserved all boars’ samples, performed pre-freeze and post-thaw analysis of the semen samples, provided input into statistical analysis and prepared an abstract with university collaborators. The experiment found no statistical differences in pregnancy rate. However, the 0.25 treatment had numerically fewer pregnant sows. To ascertain the dose most appropriate to use if semen is limited, the total number of fetuses per sow inseminated was multiplied by the number of potential doses available if only one billion motile sperm cells existed. The results suggest that the optimal dose of semen to utilize per insemination was between 0.50 and 0.75 billion motile sperm cells. Such information significantly aids the National Animal Germplasm Program in planning germplasm collections and assures that effective use of stored germplasm can be made when needed. From an industry perspective the results suggest that inseminating sows with one or two billion cells may exceed what is needed to create a pregnancy with a sufficient litter size.
Genetic security increased. Globally, genetic diversity is contracting across livestock species. Development of comprehensive ex-situ-cryopreserved germplasm collections in genebanks offers a level of genetic security for the livestock industry and research community. By building and expanding the germplasm collection the livestock industry and research community are able to access the collection’s genetic resources as needed.
Blackburn, H.D., Silversides, F., Purdy, P.H. 2009. Inseminating fresh or cryopreserved semen for maximum efficiency: implications for gene banks and industry. Poultry Science. 88:2192-2198.
Purdy, P.H., Song, Y., Silversides, F.G., Blackburn, H.D. 2009. Evaluation of Glycerol Removal Techniques, Cryoprotectants, and Insemination Methods for Cryopreserving Rooster Sperm with Implications for Breed and/or Line Regeneration. Poultry Science. 88:2184-2191
Purdy, P.H., Moce, E., Stobart, R., Murdoch, W.J., Moss, G.E., Larson, B., Ramsey, S., Graham, J.K., Blackburn, H.D. 2009. The fertility of ram sperm held for 24 hours at 5 ºC prior to cryopreservation. Animal Reproduction Sciences. 118:231-235.
Moce, E., Purdy, P.H., Graham, J.K. 2009. Treating ram sperm with cholesterol-loaded cyclodextrins improves cryosurvival. Animal Reproduction Sciences. 118:236-247.
Welsh, C.S., Stewart, T.S., Schwab, C., Blackburn, H.D. 2010. Pedigree Analysis Of Five U.S. Swine Breeds And The Implications For Genetic Conservation. Journal of Animal Science. 88:1610–1618.
Spencer, K.W., Purdy, P.H., Blackburn, H.D., Spiller, S.F., Stewart, T.S., Knox, R.V. 2010. Effect of number of motile frozen-thawed boar sperm and number of fixed-time inseminations on fertility in estrous-synchronized gilts. Animal Reproduction Sciences. 121:259-266.