The possibility of use a.f.b. rumen contents in duck feed was studied. The experimental program included a control group, fed ad libitum with duck pellets, and two experimental groups: the first fed rationed pellets and ad libitum rumen contents, and the second only with rumen contents ad libitum. The parameters observed during the trial indicate that the provision of only a.f.b. rumen contents is not sufficient for duck growth, and that the provision of ad libitum rumen contents and rationed pellets not only doesn't permit a saving of valuable feed but also has a negative effect on slaughtering traits.