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We report on a complete genome scan for quantitative trait loci ( QTL) affecting milk protein percentage ( PP) in the Italian Holstein- Friesian cattle population, applying a selective DNA pooling strategy in a daughter design. Ten Holstein- Friesian sires were chosen, and for each sire, about 200 daughters, each from the high and low tails of estimated breeding value for PP, were used to construct milk DNA pools. Sires and pools were genotyped for 181 dinucleotide microsatellites covering all cattle autosomes. Sire marker allele frequencies in the pools were obtained by shadow correction of peak height in the electropherograms. After quality control, pool data from eight sires were used for all subsequent analyses. The QTL heterozygosity estimate was lower than that of similar studies in other cattle populations. Multiple marker mapping identified 19 QTL located on 14 chromosomes ( BTA1, 2, 3, 4, 5, 6, 8, 9, 12, 14, 17, 20, 23 and 27). The sires were also genotyped for seven polymorphic sites in six candidate genes ( ABCG2, SPP1, casein kappa, DGAT1, GHR and PRLR) located within QTL regions of BTA6, 14 and 20 found in this study. The results confirmed or excluded the involvement of some of the analysed markers as the causative polymorphic sites of the identified QTL. The QTL identified, combined with genotype data of these candidate genes, will help to identify other quantitative trait genes and clarify the complex QTL patterns observed for a few chromosomes. Overall, the results are consistent with the Italian Holstein population having been under long-term selection for high PP. [ABSTRACT FROM AUTHOR]

Improvement of milk production traits in dairy sheep is required to increase the competitiveness of the industry and to maintain the production of high quality cheese in regions of Mediterranean countries with less favourable conditions. Additional improvement over classical selection could be reached if genes with significant effects on the relevant traits were specifically targeted by selection. However, so far, few studies have been undertaken to detect quantitative trait loci (QTL) in dairy sheep. In this study, we present a complete genome scan performed in a commercial population of Spanish Churra sheep to identify chromosomal regions associated with phenotypic variation observed in milk production traits. Eleven half-sib families, including a total of 1213 ewes, were analysed following a daughter design. Genome-wise multi-marker regression analysis revealed a genome-wise significant QTL for milk protein percentage on chromosome 3. Eight other regions, localized on chromosomes 1, 2, 20, 23 and 25, showed suggestive significant linkage associations with some of the analysed traits. To our knowledge, this study represents the first complete genome scan for milk production traits reported in dairy sheep. The experiment described here shows that analysis of commercial dairy sheep populations has the potential to increase our understanding of the genetic determinants of complex production-related traits. [ABSTRACT FROM AUTHOR]

A Chinese Holstein population with daughter design was analyzed using 14 microsatellites covering a map distance of 557 cM on chromosome 6 to fine map QTL for five milk production traits. 26 paternal half-sib families with 2356 daughters were involved. Two different approaches, linear regression approach and variance component approach, were employed, with a one-QTL model and two-QTL model fitted. With a one-QTL model, the linear regression approach revealed a QTL near BMS470 with effects on milk yield, fat yield, protein yield, and fat percentage, and another QTL near BMS2460 for protein percentage. The variance component approach confirmed the results of linear regression approach for the three yield traits, with the exception that the QTL for fat yield was mapped to a different position near BMS1242. The 95% confidence intervals resulted from linear regression, obtained by bootstrapping, were generally large, ranging from 31 to 53 cM, whereas the variance component approach revealed very small confidence intervals, calculated by LOD drop-off method, for the three yield traits, only 4-5 cM. With a two-QTL model, both approaches provided strong evidence for the existence of two QTLs for the three yield traits. Along with the QTLs identified in one-QTL model analyses, the linear regression approach revealed a second QTL near BP7 with effects on all the three yield traits, whereas the variance component approach located the second QTL near ILSS035, BMS470, and BP7 for the three traits, respectively. [ABSTRACT FROM AUTHOR]

Presents abstracts of several studies on animal breeding and genetics. "A Computerized Approach to Minimize Inbreeding of Breeding Plans," by John R. Garbe and Yang Da; "Efficiency of Selection on Multiple QTL in a Crossbred Population," by N. Piyasatian, R. Fernando and J. Dekkers; "Detection and Characterization of Microsatellite Loci Based on PCR," by H. Y. Chung, J. M. Ha, S. J. Oh and S. W. Lee.