Breeding values for identified quantitative trait loci under selection

International audienc

Optimizing purebred selection for crossbred performance using QTL with different degrees of dominance

A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing

Performance of Growing Pigs Fed Using Electronic Versus Commercial Feeders

The effect of electronic feeders on performance of growing boars and gilts was evaluated. Yorkshire boars and gilts (n=475) were randomly assigned to pens with single-space FIRE (electronic) feeders and pens with fivespace SMIDLEY feeders. Pigs began and ended test at an average body weight of 39 and 116 kg. Over the whole test period, pigs on electronic feeders did not differ significantly in growth rate, backfat thickness, and loin muscle area from pigs on commercial feeders. They did, however, use less feed and converted this more efficiently. Further inspection of growth and feed intake curves revealed that gilts on electronic feeders used less feed and grew slightly slower, in particular during early growth, but no differences were found for boars. Results indicate that electronic feeders may cause a genotype by environment interaction for gilts but not for boars

Regression on markers with uncertain allele transmission for QTL mapping in half-sib designs

International audienc

Analysis of Body Weight and Feed Intake Curves in Selection Lines for Residual Feed Intake in Pigs

A selection experiment for reducing residual feed intake (RFI= feed consumed over and above expected requirements for production and maintenance) in Yorkshire pigs consists of a line selected for lower RFI (LRFI) and a random control line (CTRL). Using 64 LRFI and 87 CTRL boars from generation 5 of the selection experiment, cubic polynomial random regression with heterogeneous residual variance for daily feed intake (DFI) and with homogeneous residual variance for bi-weekly body weight (BW) were identified as the best linear mixed models to describe feed intake and body weight curves. Based on the Gompertz model, significant differences in the decay parameter for DFI and in mature body weight and the inflection point for BW were observed between the lines. In conclusion, selection for lower RFI has resulted in a lower feed intake curve toward maturity, lower mature body weight, and earlier inflection points for growth

Comparison of invariant metrics and distances on strongly pseudoconvex domains and worm domains

We prove that for a strongly pseudoconvex domain $D\subset\mathbb C^n$, the infinitesimal Carath\'eodory metric $g_C(z,v)$ and the infinitesimal Kobayashi metric $g_K(z,v)$ coincide if $z$ is sufficiently close to $bD$ and if $v$ is sufficiently close to being tangential to $bD$. Also, we show that every two close points of $D$ sufficiently close to the boundary and whose difference is almost tangential to $bD$ can be joined by a (unique up to reparameterization) complex geodesic of $D$ which is also a holomorphic retract of $D$. The same continues to hold if $D$ is a worm domain, as long as the points are sufficiently close to a strongly pseudoconvex boundary point. We also show that a strongly pseudoconvex boundary point of a worm domain can be globally exposed, this has consequences for the behavior of the squeezing function

Interval mapping of quantitative trait loci with selective DNA pooling data

Selective DNA pooling is an efficient method to identify chromosomal regions that harbor quantitative trait loci (QTL) by comparing marker allele frequencies in pooled DNA from phenotypically extreme individuals. Currently used single marker analysis methods can detect linkage of markers to a QTL but do not provide separate estimates of QTL position and effect, nor do they utilize the joint information from multiple markers. In this study, two interval mapping methods for analysis of selective DNA pooling data were developed and evaluated. One was based on least squares regression (LS-pool) and the other on approximate maximum likelihood (ML-pool). Both methods simultaneously utilize information from multiple markers and multiple families and can be applied to different family structures (half-sib, F2 cross and backcross). The results from these two interval mapping methods were compared with results from single marker analysis by simulation. The results indicate that both LS-pool and ML-pool provided greater power to detect the QTL than single marker analysis. They also provide separate estimates of QTL location and effect. With large family sizes, both LS-pool and ML-pool provided similar power and estimates of QTL location and effect as selective genotyping. With small family sizes, however, the LS-pool method resulted in severely biased estimates of QTL location for distal QTL but this bias was reduced with the ML-pool