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Guelph's extender as compared to BL, significantly improved sow fertility after 3 days of storage (72.4 p. 100 versus 62.5 p. 100 for Guelph and BL!, respectively (p < 0.001). Use of Guelph's extender might allow to preserve semen until 4 days after collection without any sudden decrease in fertility and prolificacy. Fertility was significantly improved when using the total fraction of ejaculate instead of the rich one (67.9 p. 100 versus 60.7 p. 100) (p < 0.02). It was also significantly improved when using a strong dilution instead of a weak one (67.2 p. 100 versus 61.2 p. 100 for 30 and 120 X 10" spz/ml, respectively (p < 0.05).

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However, the rate of increase showed wide individual variation.At 80 kg liveweight, backfat androstenone content was not affected by the social condi-itions during rearing. At 95 kg (slaughter weight in experiment 1), the mean adrostenone content was unaffected by the social conditions : however, the proportion of animals exhibiting no increase in androstenone content between 80 and 95 kg was significantly higher in those reared with no contact with females ( fig. 2). At 107 kg (slaughter weight in experiment 2), the mean androstenone content was significantly higher when the animals were reared in collective pens (table 3).Neither experiment showed any relationship between backfat androstenone content and production parameters (feed intake, growth performance, feed efficiency). The coefficients of correlation between androstenone and carcass characteristics were not significant in experiment 1. In experiment 2, where the androstenone content was higher, a positive significant relationship was observed between the androstenone and the parameters closely related to the proportion of carcass muscle (table 4).Introduction.

les performances de croissance et les caractéristiques de la composition corporelle a été étudiée chez le Rat blanc après le sevrage. A cet effet, l'amidon de maïs et le saccharose ont été introduits, seuls ou en association, dans des mélanges alimentaires renfermant 12 , 14 ou 1 6 p. 100 de protéines sous forme de caséine. L'association des deux glucides en quantités égales dans les mélanges alimentaires permet d'augmenter le niveau spontané de leur consommation. A un taux azoté donné (14 p. 100), la vitesse de croissance est améliorée de 22 p. 100 par rapport à celles observées lorsque les régimes contiennent un seul glucide, que celui-ci soit l'amidon ou le saccharose. D'autre part, l'évolution selon l'âge de la consommation après le sevrage provoque, avec les régimes riches en saccharose, une augmentation des teneurs en lipides des carcasses, lorsque le taux azoté est faible (12 p. 100). Cette différence de la composition corporelle par rapport à celle obtenue avec les régimes riches en amidon n'apparaît p 3 .S lorsque le taux azoté est élevé (1 6 p. 100).