GENETIC-PARAMETERS FROM FACTORIAL CROSS BREEDING IN 2 DUCK STRAINS (ANAS-PLATYRHYNCHOS) BROWN TSAIYA AND PEKIN, FOR GROWTH AND FATTY LIVER TRAITS

1. A total of 655 mule ducklings were produced in three hatches by art ificial insemination of common duck females Brown Tsaiya and Pekin ''A lienor'' and of their 2 reciprocal crossbreds with Muscovy semen. 2. T hey 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 subsequ ently force fed by 2 crammers, twice a day, from the age of 85 d and f or 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'' we ight, 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 prese nt 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 darns 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 relea se rate was 35.1, 40.5, 38.2 and 46.0%. 5. The estimated differences b etween Pekin and Tsaiya genetic effects in their mule progeny were sig nificant and in favour of the Pekin, except for the number of force fe d meals and for the serous melting rate. Grandmother genetic effects w ere not significant, but maternal heterosis h(m) was in general signif icant and favourable: it was 8.5% for birth weight, about 4% for growt h traits and ''paletot'' weight, 6.2% for fatty liver weight and -2.8% (not significant) for fat release rate. A crossbreeding system betwee n a heavier Pekin breed and Tsaiya would be worth considering to impro ve the fatty liver production of mule ducks.