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In a series of papers, alternative models for QTL detection in livestock are proposed and their properties evaluated using simulations. This first paper describes the basic model used, applied to independent half-sib families, with marker phenotypes measured for a two or three generation pedigree and quantitative trait phenotypes measured only for the last(More)
Classical selection for increasing prolificacy in sheep leads to a concomitant increase in its variability, even though the objective of the breeder is to maximise the frequency of an intermediate litter size rather than the frequency of high litter sizes. For instance, in the Lacaune sheep breed raised in semi-intensive conditions, ewes lambing twins(More)
Canalising selection is handled by a heteroscedastic model involving a genotypic value for the mean and a genotypic value for the log variance, associated with a single phenotypic value. A selection objective is proposed as the expected squared deviation of the phenotype from the optimum, of a progeny of any candidate for selection. Indices and approximate(More)
Simulations were used to study the influence of model adequacy and data structure on the estimation of genetic parameters for traits governed by direct and maternal effects. To test model adequacy, several data sets were simulated according to different underlying genetic assumptions and analysed by comparing the correct and incorrect models. Results showed(More)
Bovine dermatophilosis is a severe skin infection of tropical ruminants inducing a severe loss in productivity and a 15% mortality rate. This disease is caused by the actinomycete bacterium Dermatophilus congolensis associated with the tick Amblyomma variegatum. Currently there are no prospects for a vaccine, and acaricide or antibiotic control is hampered(More)
Susceptibility to scrapie is largely controlled by the PRNP gene in mice and in several other species. However, individuals with identical scrapie susceptibility Prnp alleles may have very different incubation periods, suggesting the influence of other environmental and genetic factors. To detect loci influencing susceptibility to TSE, two mouse lines(More)
In this paper, we compare four different methods of dealing with the unknown linkage phase of sire markers which occurs in the detection of quantitative trait loci (QTL) in a half-sib family structure when no information is available on grandparents. The methods are compared by considering a Gaussian approximation of the progeny likelihood instead of the(More)
Inheritance of the ovulation rate (OR) in the Lacaune meat breed was studied through records from a small nucleus of 36 hyper-prolific ewes screened on farms on the basis of their natural litter size, and from progeny data of three selected Lacaune sires. These sires were chosen at the AI centre according to their breeding values estimated for the mean and(More)
The objective was to evaluate the potential use of genotype probabilities to handle records of non-genotyped animals in the context of survival analysis. To do so, the risks associated with the PrP genotype and other transmission factors in relation to clinical scrapie were estimated. Data from 4049 Romanov sheep affected by natural scrapie were analyzed(More)
With dense genotyping, many choices exist for methods to detect quantitative trait loci (QTL) in livestock populations. However, no across-species study has been conducted on the performance of different methods using real data. We compared three methods that correct for relatedness either implicitly or explicitly: linkage and linkage disequilibrium(More)