Detection and analysis of quantitative trait loci affecting production and secondary traits on chromosome 7 in Israeli Holsteins

A total of 5,459 Israeli Holstein cows, daughters of 11 sires, were genotyped for 29 microsatellites spanning chromosome 7 and analyzed by the daughter design for 9 economic traits: milk, fat, and protein yield, fat and protein percentage, somatic cell score, female fertility, herd life, and milk persistency. Quantitative trait loci at chromosome-wise 0.05 significance were obtained for fat and protein yield, fat percentage, somatic cell score, and female fertility. Peak F-values were obtained at 29 cM for fat and protein yield and fat percentage, at 60 cM for somatic cell score, at 74 cM for herd life, and at 11 cM for female fertility. The 0.95 confidence intervals for quantitative trait loci locations were 20 cM for kilograms of fat, 27 cM for fertility, and 51 cM for somatic cell score. Two loci affecting fertility at opposite ends of the chromosome are apparently segregating in the population. A quantitative trait locus for fertility near the centromere was confirmed by application of the modified granddaughter design to a single family. Estimated frequency of the economically favorable allele in the Israeli Holstein cattle was less than 0.5. Significant genetic gain for fertility seems possible by marker-assisted selection.