7Ekurem E, Ryohei Y, Koji T. Comparative studies on growth and meat production of ducks malland, cheng valley and their crassbred free ranged in paddy fields[J]. Jpn. Poult. Sci., 1996,33:198 -204.
8Yoshitakao, Takafumi G. Comparative studies of muscle histochemical characteristics of ducks between free ranged and housed, and among three types of breeds[J]. Jpn. Poult. Sci., 1998,35:367 -375.
9Xiang L. The effects of integrated azolla dudk rice farming system on weeding, pest control and the behaviour of ducks[J]. Jpn. J. Livest Management, 1998, 34(1) : 13 - 22.
