A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge

This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A short-term divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following artificial and natural infection were 0.49 and 0.70 respectively within a period of one week, and 0.22 and 0.41 respectively for periods separated by intervals of 7 weeks; the heritabilities of the single egg count were 0.22 and 0.38 respectively. The genetic correlation was 0.87: the FEC recorded under natural or artificial infection appear to depend on the same genetic potential

Genetic analysis of emotional reactivity in sheep: effects of the genotypes of the lambs and of their dams

A total of 1347 weaned lambs from eight genotypes were tested over five consecutive years: Romanov (ROM) and Lacaune (LAC) pure breeds, the two F1 crossbreeds (RL and LR) and the offspring of ewes from these four genotypes sired with Berrichon-du-Cher rams (BCF). The lambs were individually exposed to three challenging tests involving novelty, human contact and social isolation. Ten synthetic variables were used to express social reactivity (i.e., active vs. passive strategy), exploratory activity and reactivity to humans. BCF crossbreds were more active (i.e., high bleats, locomotion and attempts to escape) than purebreds and F1. In contrast, ROM expressed more passive responses (i.e., low bleats and vigilance postures) than LAC and BCF crossbreds. In addition, ROM approached a motionless human less and had longer flight distances to an approaching human than did LAC and BCF crossbreds. When restrained, ROM, and to a lesser extent B×ROM and B×LR, avoided human contact more than did LAC, RL and B×LAC. Most of these differences were explained by direct additive genetic effects while maternal influences or heterosis effects were rarely significant. The highest heritability was for high bleats (h2 = 0.48). Females were more active and avoided human contact more than did males

Simulation analysis to test the influence of model adequacy and data structure on the estimation of genetic parameters for traits with direct and maternal effects

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 that omission of one of the random effects leads to an incorrect decomposition of the other components. If maternal genetic effects exist but are neglected, direct heritability is overestimated, and sometimes more than double. The bias depends on the value of the genetic correlation between direct and maternal effects. To study the influence of data structure on the estimation of genetic parameters, several populations were simulated, with different degrees of known paternity and different levels of genetic connectedness between flocks. Results showed that the lack of connectedness affects estimates when flocks have different genetic means because no distinction can be made between genetic and environmental differences between flocks. In this case, direct and maternal heritabilities are under-estimated, whereas maternal environmental effects are overestimated. The insufficiency of pedigree leads to biased estimates of genetic parameters

Genetic resistance of sheep to gastrointestinal strongyles

Selective breeding of animals resistant to gastrointestinal strongyles is one of the possible answers to increasing anthelmintic resistance in sheep farming. It is currently feasible, based on the estimation of the faecal egg count in natural or experimental infections. However, this technique is too complicated for very large herds. The identification of genetic markers or mutations associated with resistance could predict the genetic value of each individual without measuring phenotypes. Molecular tools for this genetically-assisted selective breeding are currently under development. Potential limits of selective breeding for host resistance to gastrointestinal nematodes, such as an increased susceptibility to other pathogens (virus, bacteria and protozoa) or a possible adaptation of these parasites to resistant hosts, are discussed.La sélection génétique d'animaux résistants aux strongles gastro-intestinaux est une des réponses possibles au développement des résistances aux anthelminthiques dans les élevages ovins. Sa mise en oeuvre pratique est possible dès maintenant grâce à l'estimation de l'intensité de l'excrétion d'oeufs dans les matières fécales en infestations naturelles ou artificielles. Toutefois, cette technique est trop lourde à développer sur de très grands effectifs. La sélection assistée par marqueurs proches de gènes de résistance ou encore mieux par les mutations des gènes eux-mêmes pourrait prédire la valeur génétique d'un individu à la naissance sans passer par une mesure ultérieure de son phénotype. Les outils moléculaires de cette sélection sont actuellement à l'étude. Les limites potentielles de la sélection génétique sur la résistance aux nématodes gastro-intestinaux, comme une plus grande sensibilité à d'autres pathogènes (virus, bactéries ou protozoaires) ou une adaptation des parasites à des hôtes résistants, sont abordées et discutées

Network on « Genetics of adaptation and animal welfare »

Relations between genetics and animal welfare raise numerous questions as genetic characteristics are involved in many aspects of animals’ abilities to adapt to farming conditions, whether intensive or extensive. These questions are related to the genetic mechanisms of adaptation, to the consequences on animal welfare of the selection implemented up until now, and to the future improvements of the selection process. A network on the genetics of adaptation and animal welfare was built up within the multidisciplinary project “Agri Bien-être Animal” to review current knowledge. It aims also at providing usable references for regulatory discussions, as well as promoting synergies and exchanges between research units, development organisations and breeders.Les interrogations sur les relations entre génétique et bien-être des animaux sont d'autant plus nombreuses que les caractéristiques génétiques interviennent dans de nombreuses composantes des capacités d'adaptation des animaux à leurs conditions d'élevage, que celles-ci soient intensives ou extensives. Les questions portent à la fois sur les mécanismes génétiques de l'adaptation, les conséquences en matière de bien-être des sélections opérées jusqu'à présent et la conduite à tenir dans les futurs schémas de sélection. Un réseau Génétique de l'adaptation et bien-être a donc été créé au sein du programme interdisciplinaire INRA « Agri Bien-être Animal » pour faire le point des connaissances acquises. L'objectif est de fournir ainsi des références utilisables lors des discussions réglementaires et de faciliter les synergies et les échanges entre unités de recherche, organismes de développement et professionnels de la sélection

Quantitative trait loci linked to PRNP gene controlling health and production traits in INRA 401 sheep

In this study, the potential association of PrP genotypes with health and productive traits was investigated. Data were recorded on animals of the INRA 401 breed from the Bourges-La Sapinière INRA experimental farm. The population consisted of 30 rams and 852 ewes, which produced 1310 lambs. The animals were categorized into three PrP genotype classes: ARR homozygous, ARR heterozygous, and animals without any ARR allele. Two analyses differing in the approach considered were carried out. Firstly, the potential association of the PrP genotype with disease (Salmonella resistance) and production (wool and carcass) traits was studied. The data used included 1042, 1043 and 1013 genotyped animals for the Salmonella resistance, wool and carcass traits, respectively. The different traits were analyzed using an animal model, where the PrP genotype effect was included as a fixed effect. Association analyses do not indicate any evidence of an effect of PrP genotypes on traits studied in this breed. Secondly, a quantitative trait loci (QTL) detection approach using the PRNP gene as a marker was applied on ovine chromosome 13. Interval mapping was used. Evidence for one QTL affecting mean fiber diameter was found at 25 cM from the PRNP gene. However, a linkage between PRNP and this QTL does not imply unfavorable linkage disequilibrium for PRNP selection purposes

Genetic parameters for�resistance to the Salmonella abortusovis vaccinal strain Rv6 in sheep

An experimental population (1216 lambs from 30 sires) of the Inra401 sheep was created in an Inra flock to allow QTL detection for susceptibility to Salmonella infection, wool and carcass traits. The Inra401 is a sheep composite line developed from two breeds: Berrichon du Cher and Romanov. At 113 days of age on average, the lambs were inoculated intravenously with 10(8 )Salmonella abortusovis Rv6 (vaccinal strain). They were slaughtered 10 days after the inoculation. Several traits were measured at inoculation and/or slaughtering to estimate the genetic resistance of the lambs to Salmonella infection: specific IgM and IgG1 antibody titres, body weight loss, spleen and pre-scapular node weights and counts of viable Salmonella persisting in these organs. This paper presents a quantitative analysis of the genetic variability of the traits related to salmonellosis susceptibility. The heritabilities of the traits varied between 0.10 and 0.64 (significantly different from zero). Thus, in sheep as well as in other species, the determinism of resistance to Salmonella infection is under genetic control. Moreover, the correlations between the traits are in agreement with the known immune mechanisms. The genetic variability observed should help QTL detection

Les objectifs et les critères de sélection. Adaptation des ovins aux conditions de milieux difficiles

National audienceLes qualités d’adaptation des animaux aux conditions de milieu ne sont pas prises en compte actuellement de façon explicite dans les schémas de sélection, ni dans l’organisation du croisement, ni dans la production ovine en général. Ces caractères d’adaptation ou de rusticité sont cependant a priori des facteurs primordiaux de réussite économique de l’élevage en milieu contraignant ou peu maîtrisé. De telles formes d’élevage sont appelées à se développer dans le cadre des grandes orientations européennes de revalorisation de zones marginales et de protection de l’environnement, et il importe d’adapter sinon de redéfinir les programmes génétiques en fonction de ces nouvelles données. Une approche de ces problèmes (Bibé et Vissac) consiste à faire l’hypothèse que les performances zootechniques sont la résultante, sinon la somme, des expressions globales de "gènes de production" et de "gènes d’adaptation" dans le milieu d’élevage ; une sélection basée sur le contrôle des performances dans les conditions de la production permettrait alors de progresser globalement sans trop d’erreurs, à la fois sur les aptitudes de production et les qualités d’adaptation requises. Cette démarche est cependant imparfaite, particulièrement dans le cas de productions en milieux difficiles, car les contraintes d’environnement y sont par définition mal maîtrisées, et par conséquent les parts respectives des qualités d’adaptation et de production dans l’expression des performances sont fluctuantes. D’un autre point de vue, il est a priori plus efficace de travailler sur les composantes d’un phénomène plutôt que sur leur résultante dans la mesure où elles ne sont pas étroitement corrélées. Une autre approche consiste donc à étudier les éléments de la rusticité au même titre que les performances zootechniques classiques, pour tenter de valoriser leur éventuelle variabilité génétique intra ou inter races selon les méthodes d’amélioration génétique adéquates. Les actions dans lesquelles la SAGA (Station d’amélioration génétique des animaux - INRA) est impliquée, portant sur les caractères d’adaptation des ovins relèvent de cette double réflexion

Les sols et l'élevage

National audienc

High genetic correlation between resistance to Haemonchus contortus and to Trichostrongylus colubriformis in INRA 401 sheep

International audienc