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Little is known about epigenetic mechanisms in birds with the exception of the phenomenon of dosage compensation of sex chromosomes, although such mechanisms could be involved in the phenotypic variability of birds, as in several livestock species. This paper reviews the literature on epigenetic mechanisms that could contribute significantly to trait variability in birds, and compares the results to the existing knowledge of epigenetic mechanisms in mammals. The main issues addressed in this paper are: (1) Does genomic imprinting exist in birds? (2) How does the embryonic environment influence the adult phenotype in avian species? (3) Does the embryonic environment have an impact on phenotypic variability across several successive generations? The potential for epigenetic studies to improve the performance of individual animals through the implementation of limited changes in breeding conditions or the addition of new parameters in selection models is still an open question.

Genetic parameters of traits related to hepatic lipid metabolism, carcass composition, and product quality of overfed mule ducks were estimated on both parental lines of this hybrid: the common duck line for the maternal side and the Muscovy line for the paternal side. The originality of the statistical model was to include simultaneously the additive genetic effect of the common ducks and that of the Muscovy ducks, revealing a greater genetic determinism in common than in Muscovy. Plasma metabolic indicators (glucose, triglyceride, and cholesterol contents) were heritable, in particular at the end of the overfeeding period, and heritabilities increased with the overfeeding stage. Carcass composition traits were highly heritable in the common line, with values ranging from 0.15 for liver weight, 0.21 for carcass weight, and 0.25 for abdominal fat weight to 0.32 for breast muscle weight. Heritabilities of technological outputs were greater for the fatty liver (0.19 and 0.08, respectively, on common and Muscovy sides for liver melting rate) than for the pectoralis major muscle (between 0.02 and 0.05 on both parental sides for cooking losses). Fortunately, the processing industry is mainly facing problems in liver quality, such as too high of a melting rate, than in meat quality. The meat quality appraisal criteria (such as texture and cooking losses), usually dependent on pH and the rate of decline of pH, were also very lowly heritable. This study demonstrated that genetic determinism of meat quality and ability of overfeeding is not similar in the common population and in the Muscovy population; traits related to fattening, muscle development, and BW have heritability values from 2 to 4 times greater on the common line than on the Muscovy line, which is relevant for considering different selection strategies.

-The analysis concerned 546 ejaculates from 65 bucks from two strains ('1601', a duplicate of the 'Verde' strain from INIA-Valencia, Spain-and '2066' from INRA, France) and their two reciprocal crosses, recorded during a 210 day period spanning from August 1996 to February 1997. Two ejaculates were collected from each buck every three weeks and semen traits were recorded every six weeks when the semen was used for insemination. All semen traits were recorded for both ejaculates except concentration, which was recorded only for the ejaculate selected for insemination (the better of the two ejaculates for mass motility). On average, mass motility (scale of Petitjean, 1965 [24]) was 6.75 (standard deviation 1.01), pH 7.28 (0.33), volume 0.62 mL (0.19 mL), percent of motile spermatozoa (PMS) 70.1% (7.5%), concentration 492 × 10 6 spz·mL -1 (142 × 10 6 ), the total number of spermatozoa per ejaculate (TSE) 321 × 10 6 (110 × 10 6 ) and the number of motile sperms per ejaculate (MSE) 231 × 10 6 (83 × 10 6 ). Both strains had similar performances except for the volume of the ejaculate (1601: 0.67 ± 0.04 mL; 2066: 0.52 ± 0.04 mL) and PMS (1601: 69.8 ± 1.4%; 2066: 66.4 ± 1.4%). There was a significant heterosis effect for concentration (37.5% of the parental average), mass motility (6.8%) and PMS (4.1%). Heterosis for the synthetic criteria TSE and MSE amounted to 37.6% and 42.3%, respectively. Strain differences in maternal effects were evidenced: strain 1601 exhibited favourable maternal effects on volume, PMS and mass motility.rabbit / semen / heterosis / maternal effects Résumé -Hétérosis et effets maternels sur les caractéristiques de la semence de lapin. L'analyse concerne 546 éjaculats issus de 65 mâles de deux souches ('1601', issue par duplication de la souche 'Verde'de l'INIA-Valencia, Espagne-et '2066'de l'INRA, France) et de leurs deux croisements réci-proques, contrôlés pendant 210 jours entre août 1996 et février 1997. Les mâles sont prélevés toutes les 3 semaines (2 éjaculats), mais les caractéristiques de la semence sont mesurées toutes les 6 semaines, lors de l'insémination. Tous les caractères sont contrôlés sur les 2 éjaculats sauf la concentration, mesurée uniquement sur l'éjaculat sélectionné pour l'insémination (le meilleur des 2 sur la motilité (0)5 61 28 53 53; e-mail: brun@toulouse.inra.fr massale). En moyenne, la motilité massale (échelle de Petitjean, 1965 [24]) est de 6,75 (écart-type de 1,01), le pH de 7,28 (0,33), le volume de 0,62 mL (0,19 mL), le pourcentage de spermatozoïdes motiles (PMS) de 70,1 % (7,5 %), la concentration 492 × 10 6 spz·mL -1 (142 × 10 6 ), le nombre total de spermatozoïdes par éjaculat (TSE) de 321 × 10 6 (110 × 10 6 ) et le nombre de spermatozoïdes motiles par éjaculat (MSE) de 231 × 10 6 (83 × 10 6 ). Les deux souches ont des performances identiques sauf pour le volume de l'éjaculat (1601 : 0,67 ± 0,04 mL ; 2066 : 0,52 ± 0,04 mL) et PMS (1601 : 69,8 ± 1,4 % ; 2066 : 66,4 ± 1,4 %). On observe un effet d'hétérosis significatif sur la concentration (37,5 % de...

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