Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: April 21, 2005
Publication Date: July 1, 2005
Citation: Sonstegard, T.S., Van Tassell, C.P. 2005. Characterization of fezl effects on scs in a sample of north american Holsteins [abstract]. ADSA/ASAS Joint Meeting. p. 248.
Previous mapping studies using overlayed daughter designs had identified a putative quantitative trait nucleotide (QTN) affecting somatic cell count within the coding region of the forebrain embryonic zinc finger-like (FEZL) gene. Cows inheriting the variant of FEZL with a glycine stretch of amino acids reduced from 13 to 12 amino acids tended to have lower somatic cell counts during first lactation. In order to validate the utility of this potential QTN in selection for dairy health, we conducted a substitution analysis on a sample of North American dairy sires. Bovine sequence traces were obtained for regions of FEZL flanking the QTN. PCR amplicons from genomic DNA were sequenced to design primers to assay QTN genotypes. FEZL QTN genotypes were generated for 2,379 dairy bulls. The deletion variant of FEZL was not identified in a group of influential Jersey sires (N=49). In Holsteins, the allele frequency of the deletion variant was less than 3% (N=2,325). Estimates of allele substitution effect were obtained using MTDFREML with a model that included a polygenic effect and a FEZL genotype effect with daughter deviations for somatic cell score as the phenotypic data. The estimates were based on the differences between estimated genotypic effects of the heterozygote and the common homozygote because only six homozygotes for the deletion variant were observed. The heritability of the trait was estimated to exceed 90%, because the deviations have been adjusted for all non-genetic effects and accumulated across daughters. The estimated allele substitution effects were 0.006, 0.005, 0.018, 0.026, and 0.043 units of SCS for heritabilities of 0.95 (REML estimate), 0.50, 0.10, 0.05, and 0.01, respectively. Previous analyses of the DGAT1 QTN showed allele effects that were much more robust to heritabilities using a similar analysis model. The extreme allele frequency of FEZL may be partially responsible for this phenomenon. Further analysis of this QTN is necessary before selection based on FEZL variants can be recommended.