6WORKEL H A, KELLER T, REEVE A, et al. Cho- line-the rediscovered vitamin for poultry [ J ]. World Poultry,1998(10) :22 -25.
7EMMERT J L, GARROW T A, BAKER D H. Hepatic betaine-homocysteine methyltransferase activity in the chicken is influenced by dietary intake of sulfur amino acids, choline and betaine [ J ]. Nutrition, 1996, 126 (8) :2050-2058.