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

Segregation of a major gene influencing ovulation in progeny of Lacaune meat sheep

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 the variability of their daughters' litter size. Non-carrier Lacaune dairy ewes were inseminated to produce 121 F1 daughters and 27 F1 sons. Twelve sons (four from each sire) were used in turn to inseminate non-carrier Lacaune dairy ewes providing 260 BC progeny ewes. F1 and BC progeny were brought from private farms and gathered after weaning on an experimental farm where ovulation rates were recorded in the first and second breeding seasons. With an average of 6.5 records each, the mean OR of hyper-prolific ewes was very high (5.34), and 38.4% of records showed a rate of 6 or more. F1 data showed high repeatability of OR (r = 0.54) within ewe, with significant variability among ewes. High OR (≥ 4) were observed in each family. A segregation analysis provided a significant likelihood ratio and classified the three founders as heterozygous. BC ewes also displayed high repeatability of OR (r = 0.47) and the mean OR varied considerably between families (from 1.24 to 1.78). Seven of the 12 BC families presented high-ovulating ewes (at least one record ≥ 4) and segregation analysis yielded a highly significant likelihood ratio as compared to an empirical test distribution. The high variability of the mean ovulation rate shown by a small group of daughters of BC ewes inseminated by putative carrier F1 rams, and the very high ovulation rate observed for some of these ewe lambs, confirmed the segregation of a major gene with two co-dominant alleles borne by an autosome. The difference between homozygous non-carriers and heterozygous ewes was about one ovulation on the observed scale and 2.2 standard deviations on the underlying scale

L'association mais-soja en culture fourragere.

National audienc

Les leçons d'une épidémie de tremblante du mouton

"Chantier qualité spécifique "Auteurs Externes" département de Génétique animale : uniquement liaison auteur au référentiel HR-Access "National audienc

Organisation à l’Inra des observations et expérimentations sur des animaux modèles ou agronomiques infectés par une encéphalopathie spongiforme transmissible

National audienceThe investments at INRA for the study of transmissible spongiform encephalopathy (TSE) in animal populations, on farms or in experimental conditions are described : a large scale PrP gene genotyping laboratory, the experimental farm of Langlade where sheep submitted to natural scrapie are followed, an important protected animal building (Installations Nationales Protégées pour l’étude des Encéphalopathies Spongiformes Transmissibles “INPREST”) for large farm animals, the sheep house of the Toulouse National Veterinary School (ENVT), the protected rodent buildings on the INRA sites of Nouzilly and Jouy-en-Josas and Toulouse (ENVT). All these investments give scientists the means necessary to carry out their investigations on the physiopathology of animal TSE, the genetic determinants of the sensitivity/ resistance of these pathologies, the nature of the pathogenic agent and notably its variability as well as the evaluation of risks and the diagnostic.Les investissements mis en place par l’INRA pour aborder l’étude des Encéphalopathies Spongiformes Transmissibles (EST) dans les populations animales, de ferme ou en conditions expérimentales, sont décrits : laboratoire de génotypage du gène PrP à grande échelle, domaine expérimental de Langlade où sont suivis des ovins soumis à une tremblante naturelle, très grande animalerie protégée (Installations Nationales PRotégées pour l’étude des Encéphalopathies Spongiformes Transmissibles « INPREST ») pour les gros animaux de ferme, bergerie protégée de l’Ecole Nationale Vétérinaire de Toulouse (ENVT), animaleries rongeurs protégées sur les sites INRA de Nouzilly et Jouy-en-Josas, et de Toulouse (ENVT). Cet ensemble d’investissements donne aux scientifiques les moyens de mener à bien leurs investigations sur la physiopathologie des EST animales, les déterminants génétiques de la sensibilité/résistance à ces pathologies, la nature de l’agent pathogène et notamment sa variabilité, ainsi que sur l’évaluation des risques et le diagnostic

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

International audienc

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

Génétique de la sensibilité à la tremblante ovine: recherches en cours et perspectives

National audienceIn several species (man, mouse, sheep), the susceptibility to transmissible subacute spongiform encephalopathies is highly regulated by the host genotype, A major part of the observed genetic variability depends on one gene, This gene is likely the Prn-p gene, which codes for the host prion protein PrP, According to an hypothesis supported by several authors, this protein could be the causal agent of these diseases or it could be associated with the causal agent, Molecular analysis of the structure of the Prn-p gene in sheep demonstrates segregating alleles that differ from each other by a single mutation, It could be interesting, therefore, to examine the possibility of controlling scrapie in sheep by selective breeding on the basis of laboratory analyses of the Prn-p gene polymorphism. Before selecting against this susceptibility however, different questions need to be answered: Could resistant animals act as a source of infection? Could animals resistant to one scrapie strain be susceptible to another? How expensive would such a selection scheme be? How should the selection be organised in practice?Dans plusieurs espèces (homme, souris, mouton), la sensibilité aux encéphalopathies spongiformes subaiguës transmissibles (ESST) est largement contrôlée par le génotype de l’hôte. Une part majeure de la variabilité génétique observée vient d’un gène, dont plusieurs arguments permettent de penser qu’il s’agit du gène Prn-pcodant pour la protéine prion PrP, qui pourrait, selon certains auteurs, être l’agent causal de ces pathologies ou être associé à ce dernier. L’analyse moléculaire de la structure du gène Prn-p chez le mouton montre la ségrégation d’allèles différant les uns des autres par une mutation ponctuelle. Une sélection pour la résistance à la tremblante, basée sur des analyses en laboratoire du gène Prn-p, est donc envisageable dans cette espèce. La mise en place d’une telle sélection pose cependant plusieurs problèmes théoriques et pratiques : les animaux résistants pourraient-ils constituer un réservoir d’infection ? Les animaux résistants à une souche de tremblante pourraient-ils se révéler sensibles à une autre ? Le coût de cette sélection est-il acceptable ? Comment l’organiser au mieux