Effect of lnbreeding and Crassing on Laying Performance ot Egg-ducks

In this research,the inbred lines of different inbreeding levels were established by usingthe source of Putian Black Duck. The egg-laying performance by duck at the age of 300 days wasdetermined and the result showed that 12.5% inbreeding levels had less influence on economiccharacters.When the inbreeding levels increased by 10% each time,the average depression rates ofthe three kinds of characters,i.e. the initial laying age,egg number and egg weight at 300 day agewere 18.3%, 14.2% and 2.0% respectively. In this experiment,when the inbreeding level was21.9%, the characters showed serious inbreeding depression. The selected inbred line with excel-lent performance was crossed with generation-selecting line W and M and the progeny F1 showedgood hybrid superiority. The rates of above-mentioned superiority of the three kinds of characterswere-6.83%,15.26% and 4.75% respectively and the crossing effects of W line was better thanthat of M line. The crossing effects produced by top cross and bottom cross were different. Thesuperiority rates of the egg number at 300 day age were 3.84% and 17.49% respectively. The ef-fect of bottom cross was better than that of top cross. The feasibility of applying the inbred line tobreeding combination was approached in this paper.