Location: Animal Disease ResearchTitle: Ovine leukocyte profiles do not associate with variation in the prion gene, but are breed-dependent Author
|Johnson, W Carl - Carl|
|Taylor, Joshua - Bret|
|Knowles, Donald - Don|
Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2015
Publication Date: 6/22/2015
Citation: Mousel, M.R., White, S.N., Herndon, D.R., Reynolds, J.O., Gonzalez, M., Johnson, W.C., Ueti, M.W., Taylor, J.B., Knowles Jr, D.P. 2015. Ovine leukocyte profiles do not associate with variation in the prion gene, but are breed-dependent. Animal Genetics. 47(1):136-37. Interpretive Summary: Modern genetics can be used to improve the health and welfare of livestock. Improved livestock health and welfare will increase the efficiency of producing human foods. Thus, studies are underway to identify genes associated with health and fitness traits. This study reports no association of sheep total white blood cell, lymphocyte, neutrophil, monocyte, eosinophil, or basophil counts with detected DNA variations in the prion gene. This is important as disease status is often dependent on the functionality of the immune system and if selection for a specific prion variation changed any of the white blood cell counts this could have increased susceptibility to other diseases. Interestingly, Suffolk sheep had greater total white blood cell, lymphocyte, neutrophil, monocyte, and basophil counts compared with the other breeds. Rambouillet sheep had the lowest counts. Similar to humans and other mammals, total white blood cell and lymphocyte counts went down as the sheep increased in age over years. Sheep producers can continue to genetically select for resistance to scrapie without changing circulating white blood cell counts.
Technical Abstract: Prion genotype in sheep confer resistance to scrapie. In cattle, lymphocyte profile has been found to be associated with prion genotype. Therefore, the aim of this study was to determine if variations in the sheep prion gene were associated with leukocyte populations as measured by complete blood cell counts (CBC). Blood was collected from 589 ewes (Columbia, Polypay, Rambouillet, Suffolk) aged 2-6 years over 3 years (2011, 2013, and 2014) at the U.S. Sheep Experiment Station, Dubois, ID. DNA was extracted, CBC were recorded, and the prion coding region was sequenced for each ewe. A reduced statistical model, which included breed, genotype, and age as fixed effects with year CBC was recorded and sire as a random effects, was analyzed with the mixed procedure of SAS 9.3. There were no associations (P>0.10) of any prion genotype with any leukocyte count except for the variant at nucleotide position 335 with monocytes (P<0.023). This difference is likely due to only 10 heterozygotes represented within this population of sheep. These results are contrary to a cattle study however, we did not differentiate the lymphocyte population into B cells, CD4+, and CD8+ T cells. Breed of sheep impacted (P<0.01) all leukocyte CBC measurements. Generally, Rambouillet ewes had lower leukocyte counts compared with the other breeds and Suffolk had the greatest. Younger sheep had greater (P<0.01) white blood cell and lymphocyte counts compared with older sheep. Ewe age did not affect (P>0.16) monocyte, neutrophil, basophil or eosinophil counts. This study did not find an association of leukocyte counts, as determined by CBC, with the 10 prion genotypic variations detected in this study.