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The performance of two crosses each including a line of Egyptian origin (Fayoumi x Leghorn and ISA x Mandarah) and a third utilizing an experimental line selected for low feed consumption during the laying phase (ISA x R-) were compared to those of a brown-egg-type commercial cross (ISA brown). The hens were kept in cages (three per cage) in a laying house equipped with windows and no specific isolation. During two periods, 20 to 35 and 45 to 50 weeks of age, the hens were fed a commercial diet. Only half of each cross were fed that diet from 36 to 44 weeks of age. In all cases, the performance of the two crosses with a local line (Fayoumi x Leghorn and ISA x Mandarah) was lower at all times compared to the other two crosses for egg laying rate, average egg weight and feed efficiency. Differences between the ISA x R- cross and the commercial Isabrown cross for the same variables were rather small, some in favor of the Isabrown (earlier age at point of lay, average egg weight, laying rate during the first weeks), others in favor of the experimental cross (laying rate after 35 weeks, and overall feed efficiency in spite of a higher body weight). The mortality rate measured at early stages or cumulated over time was always lowest for the ISA x R- cross, highest for the Isabrown cross, and intermediate for the other two crosses. In conclusion, the ISA x R- cross was overall the best in the conditions of this trial.

Abstract Chicks of both sexes issued from the cross of heterozygous K/k+ cocks for the slow-feathering sex linked K allele with k+ (rapid feathering) hens, were compared from the age of 4 to 10 weeks at two ambient temperatures. In individual cages, 30 male chicks of each genotype (K/k+ and k+/k+) were raised at 21°C, and 60 others, distributed in the same way, were raised at 31°C. 71 K/W females and 69 k+/W females were raised in a floor pen at 31°C till 10 weeks of age. In the males, the body weight, feed consumption and feed efficiency at different ages were influenced only by temperature (lower growth rate and feed intake at 31°C); no significant effects of the genotype at locus K nor genotype × temperature interaction were observed. In females, all at 31°C, the genotype (K/W or k+/W) had no significant effect on growth rate. Plumage weight and weight of abdominal fat (absolute or related to body weight) were measured on half of the males of each group in individual cages, at 10 weeks of age. Moreover, on 36 males and 48 females of the two genotypes, in a group battery at 31°C, the absolute and relative weight of plumage were measured on a sample every two weeks between 4 and 10 weeks. In the first case, no significant effect of genotype appeared. In the second case, an interaction between age and genotype was suggested from plumage weight: its growth, especially in male chicks, appears to be temporarily and unexpectedly faster from 4 to 6 weeks of age for the K/k+ and K/W genotypes.

Abstract Two Rhode Island Red egg-laying lines have been divergently selected on residual food intake (low intake R- line, high intake R+ line) for 19 generations. In addition to direct response, correlated responses have altered several other traits such as carcass adiposity and lipid contents of several tissues, the R+ animals being leaner than the R- ones. In a search for the biological origin of the differences observed in fat deposit, the hepatic mRNA amounts of genes involved in lipid metabolism were investigated. No difference was found between lines for mRNA levels of ATP citrate-lyase, acetyl-CoA carboxylase, fatty acid synthase, malic enzyme and CCAAT/enhancer binding protein α, a transcription factor acting on several lipogenesis genes. The genes coding for stearoyl-CoA desaturase and apolipoprotein A1 displayed significantly lower mRNA levels in the R+ cockerels compared to the R-. All together these mRNA levels explained 40% of the overall variability of abdominal adipose tissue weight, suggesting an important role of both genes in the fatness variability.

Les performances de ponte et d'efficacité alimentaire de la race Mandarah d'origine égyptienne, ont été comparées chez des poules en cages individuelles à deux températures constantes (21°C et 31°C) de l'entrée en ponte à l'âge de 47 semaines. La race Mandarah apparaît modérément affectée par la chaleur pour l'ensemble des critères (respectivement -10 et -6 % pour la masse d'oeufs et le poids moyen des oeufs).

Abstract This study compares laying performances between two environments of dwarf laying hen lines segregating for the naked neck mutation (NA locus), a selected dwarf line of brown-egg layers and its control line. Layers with one of the three genotypes at the NA locus were produced from 11 sires from the control line and 12 sires from the selected line. Two hatches produced 216 adult hens in Taiwan and 297 hens in France. Genetic parameters for laying traits were estimated in each environment and the ranking of sire breeding values was compared between environments. Laying performance was lower, and mortality was higher in Taiwan than in France. The line by environment interaction was highly significant for body weight at 16 weeks, clutch length and egg number, with or without Box-Cox transformation. The selected line was more sensitive to environmental change but in Taiwan it could maintain a higher egg number than the control line. Estimated heritability values in the selected line were higher in France than in Taiwan, but not for all the traits in the control line. The rank correlations between sire breeding values were low within the selected line and slightly higher in the control line. A few sire families showed a good ranking in both environments, suggesting that some families may adapt better to environmental change.

L’augmentation du poids de tissus adipeux présents dans les carcasses de poulet de chair a incité à en rechercher les causes, afin de pouvoir maîtriser ce caractère défavorable, tant pour les producteurs que pour les consommateurs. La comparaison de lignées expérimentales génétiquement grasses et maigres a permis d’identifier les différences métaboliques majeures entre animaux gras et maigres. Elles sont rappelées dans cet article. Les résultats les plus récents concernant le métabolisme hépatique, analysé à différentes étapes (catabolisme des acides aminés, lipogenèse proprement dite, maturation et sécrétion des lipides) par des mesures d’activités enzymatiques ou de quantités d’ARN messagers, sont rapportés. Ils montrent que beaucoup de ces paramètres sont plus élevés chez les animaux gras comparés aux maigres. L’hypothèse d’une régulation commune pour ces différentes étapes du métabolisme est avancée. Cependant, chaque étape peut aussi être individuellement responsable des différences d’engraissement, comme cela semble être le cas pour l’enzyme glutamate déshydrogénase.