No abstract

Aim of the present study was to confirm previously quantitative trait loci (QTL) affecting somatic cell score (SCS) on Bos taurus autosomes (BTA23) chromosomes and how can make selection by markers linked with QTL for SCS in Friesian cows in Egypt. A granddaughter design with selective genotyping was implemented that included haf-sibs from 6 sire-families cows. All sires have at least 200 daughters. Animals were genotyped for 5 microsatellites markers on BTA23. Heterozygosity on locus showed wide variation among five microsatellite markers among families. Across 6 families, the most likely QTL positions for SCS were all mapped at 48 cM, close to BM1443. Results for trait SCS, QTL with chromosome-wide significance within and across families studied identified the QTL allele substitution effects estimated for each family while fixing the QTL at the most likely position (48 cM) in 95% confidence interval (CI) QTL position. Sire families have significant QTL effect on SCS. The calculated overall QTL sire effect values across the six families (-0.154 ± 0.422), indicated decreased SCS among all families. The fact that such genotypes are found in relative high frequencies in Friesian cattle may reflect the combined breeding goal that is characterized by SCS selection to resistance mastitis. The identification of these markers raises the possibility of overcoming the unfavourable genetic correlation between milk production, SCS and mastitis traits through markerassisted selection.