Superiority of QTL-Assisted Selection in Dairy Cattle Breeding Schemes

Abstract

The superiority of selection schemes employing information about a known quantitative trait locus (QTL) over conventional schemes is examined for dairy cattle breeding schemes. Stochastic simulation of a dairy cattle population with selection practices, structures, and parameters similar to the US Holstein population was implemented. Additive genetic effects were estimated by an animal model. Two schemes were compared: a QTL-assisted selection scheme in which the genotype of a known QTL was accounted for in the animal model as a fixed factor, and a QTL-free selection scheme in which the QTL was simulated but was not fit separately in the animal model. Under the QTL-assisted selection scheme, all animals in the mixed model were assumed to be genotyped for the QTL. The effect of using QTL information on the genetic response, the frequency of the favorable QTL allele, and the accuracy of evaluation were examined. Moreover, the effect was studied in four distinct paths of selection: active sires, proven young bulls, bull dams, and first-lactation cows. Average superiority values of 4.6, 7.6, 11.7, and 1.1% for genetic response were observed over 16 yr of selection for active sires, young bulls, bull dams, and first-lactation cows, respectively. Frequency of the favorable QTL allele changed faster in bull dams than males, and was the slowest in first-lactation cows. Finally, accuracy of evaluation under the QTL-assisted selection scheme was higher than under the QTL-free selection scheme. Young bulls ofthe QTL-assisted selection scheme on average had 0.049 higher accuracy, and first-lactation cows had on average 0.185 higher accuracy than corresponding animals of the QTL-free selection scheme.

Quantitative trait loci mapping in dairy cattle: review and meta-analysis

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“…There is general agreement from theoretical and simulation studies that application of MAS has the potential to increase the rate of genetic gain especially if traditional selection is less effective [1,59]. In dairy cattle MAS could be used to pre-select young candidate bulls prior to progeny testing, thus increasing selection differentials, shortening generation interval and increasing genetic gain [45].…”

Investigation of the Use of Alternative Economic Indices and QTL-Assisted Selection for the Genetic Improvement of Production and Health Traits in Bangladeshi Dairy Cattle

“…The differences in the rate of genetic gains for somatic cell score might be due to the QTL-assisted selection that was considered on the somatic cell score basis. Traits that considered QTL-assisted selection have an impact on genetic gains, as were reported by Abdel-Azim and Freeman [11].…”

“…However, the benefits of MAS are greatest for traits with low heritability. Marker identification and use should enhance future prospects for breeding of such traits as tolerance or resistance of the environmental stresses, including diseases [11]. In addition, more benefits could be expected from MAS with more specific applications, such as early selection of animals, or by the application of dynamic procedures, i.e., letting the respective weights to QTL and polygenic values in the selection criterion vary across generations.…”

“…Several simulation studies on the impact of using QTL information has been reported in the literature (e.g., Meuwissen and van Arendonk, [13]; Ruane and Colleau [14]; Spelman and Garrick [10]; Spelman et al [15]; Abdel-Azim and Freeman [11]. Out of them, Spelman et al [15] tests the additional genetic gains of MAS, and they observed limited benefit (1.8% genetic gain) of MAS in conventional progeny testing schemes through a deterministic approach.…”