Association of a nucleotide variant in Tenascin X with objective milk production traits in US dairy sheep

Authors: HEMMERLING, KANEESHA - Washington State University; Murphy, Thomas - Tom; HERNDON, MARIA - Washington State University; MASSA, ALISHA - Washington State University; ULAS CINAR, M - Washington State University; THOMAS, DAVE - University Of Wisconsin; White, Stephen; Mousel, Michelle

Submitted to: International Society for Animal Genetics (ISAG)
Publication Type: Abstract Only
Publication Acceptance Date: 5/17/2019
Publication Date: 7/7/2019
Citation: Hemmerling, K.M., Murphy, T.W., Herndon, M.K., Massa, A.T., Cinar, M.U., Thomas, D.L., White, S.N., Mousel, M.R. 2019. Association of a nucleotide variant in Tenascin X with objective milk production traits in US dairy sheep [abstract]. International Society for Animal Genetics (ISAG). Abstract #P65 (Abstract Book p. 81). Available: https://www.isag.us/Docs/Proceedings/ISAG2019_Proceedings.pdf

Interpretive Summary:

Technical Abstract: With the world population growing by 83 million people annually, it is vital to select livestock that efficiently produce high quality products to meet increasing worldwide nutritional needs. The US is the largest importer of sheep milk cheeses in the world, and has a small, but growing dairy sheep industry. Currently there is no genetic evaluation program in the US. Therefore, identifying genomic regions that positively influence milk quantity and quality would be beneficial. In meat and wool breeds, a variation in the Tenascin X (TNXB) gene, E2004G, was associated with subjective milk score and mature bodyweight. To determine if there was an association between TNXB E2004G and objective 180 day adjusted milk production traits, 216 ewes originating from a US dairy sheep research flock were genotyped. Ewes were 2 to 6 years old and consisted of East Friesian (E), Lacaune (L), Awassi (A), and Katahdin (K) purebreds and crosses. The traits analyzed included individual milk, fat, and protein yield, and fat and protein percentage. A reduced mixed model was used with fixed effects of age, breed composition, and TNXB genotype and a random effects of sire nested within breed type and year of lactation. The effect of genotype on protein yield approached significance (P<0.06) with AG ewes producing more protein than GG ewes. There was a numerical trend for each additional A to increase milk, protein, and fat yield but the low number of AA animals reduced the power to detect statistical differences. No genotype effects for the other traits were observed (P>0.10). As expected, age impacted milk, protein, and fat yield (P<0.01) with 5 year olds produced more than 4, 3, and 2 year olds. EL crossbreds had greater milk yield than ELA and ELK ewes (P<0.04). Additional studies need to be conducted with more balanced genotype frequencies to validate these results. Gene expression in mammary tissue is being evaluated to determine whether differences in genotype affects expression. Understanding how TNXB E2004G impacts milk production may allow producers to use TNXB genotypes as a selection tool to improve dairy sheep production.