8Barton B A, Rosario H A, Anderson G W, et al. Effects of dietary crude protein, breed, parity, and health status on the fertility of dairy cows[J].J Dairy Sci , 1996(79) : 2225-2236.
9Hauglaian J M. Extending the postpartum anovulatory period in dairy cattle with estradiol cypionate[J], J Dairy Sci, 2002,85 : 3238-3249.
10Akbar A M, Reichert L E, Dunn T G. Serum levels of follicle stimulating hormone during the bovinges Irouseycle [J]. J Anim Sci , 1974, 39:360.
