Linkage disequilibrium and selection response in two-stage marker-assisted selection of dairy cattle over several generations.

A stochastic simulation was carried out to investigate the advantage of marker-assisted selection (MAS) in comparison with traditional selection over several generations. The selection goal was a sex-limited trait or a linear combination of traits with a polygenic component, two unlinked additive QTL and a non-genetic component. The simulated QTL were moderate or large and the allele frequencies were varied.

Evidence for quantitative trait loci affecting twinning rate in North American Holstein cattle.

Twinning in dairy cattle has been associated with many negative health and reproductive events that cause economic loss to the producer. Reports have suggested that twinning rates are increasing and that there may be a positive relationship between milk production and twinning frequency. Putative quantitative trait loci (QTL) for twinning and ovulation rate on bovine chromosomes 5, 7, 19 and 23 have been previously identified in other populations.

Indirect prediction of herd life in Guernsey dairy cattle.

Production and type data were used to investigate the relationships of these traits with herd life data in US Guernsey cows that calved from 1985 through 1990. Two definitions of herd life were used: actual days from birth to disposal (true herd life) and herd life adjusted for milk production (functional herd life). Genetic parameters were calculated with data from cows that had an opportunity to reach 84 mo of age (n = 18,725).

Twinning rates for North American Holstein sires.

Calving data of North American Holsteins were analyzed using a linear sire model and a threshold sire model to estimate fixed effects and sire predicted transmitting abilities (PTA) for twinning rate. The data were 1,324,678 births of 37,174 sires of cows from the National Association of Animal Breeders (NAAB) calving ease database. All twins were assumed to be dizygotic.