RESUMEN
1. A total of 655 mule ducklings were produced in three hatches by artificial insemination of common duck females Brown Tsaiya and Pekin "Alienor" and of their 2 reciprocal crossbreds with Muscovy semen. 2. They were fed ad libitum until 6 weeks, then restricted to one meal per day until day 75 and afterwards preforce fed until day 84 and subsequently forced fed by 2 crammers, twice a day, from the age of 85 d and for a maximum of 13 d. 3. Body weight at hatching, 28 d, 56 d, 75 d, 84 d and at slaughter, the number of force-fed meals, the "paletot" weight, the fatty liver weight, the fat release rate after sterilisation of a 60 g portion of liver and the serous melting rate were measured individually. 4. Significant dam genotype and hatch effects were present for all traits. The crammer effect on force feeding traits was also significant. For mule ducks from Brown Tsaiya, Tsaiya x Pekin, Pekin x Tsaiya and Pekin dams respectively, mean body weight was 2356, 3219, 3137 and 3801 g at 12 weeks, "paletot" weight was 1585, 2111, 2110 and 2470 g, fatty liver weight was 441, 585, 563 and 641 g, fat release rate was 35.1, 40.5, 38.2 and 46.0%. 5. The estimated differences between Pekin and Tsaiya genetic effects in their mule progeny were significant and in favour of the Pekin, except for the number of force fed meals and for the serous melting rate.(ABSTRACT TRUNCATED AT 250 WORDS)