3Spell AR,Beal WE,Corah LR,el al.Evaluating recipient and embryo factors that affect pregnancy rates of embryo transfer in beef cattle[J].Theriogenology.2001,15,56(2):287-97.
4Overstrom EW.In vitro assessment of embryo viability[J].Theriogenology.1996,45(1):32-37.
5Lindner GM,Wright RW.Bovine embryo morphology and evaluation[J].Theriogenogy.1983,20(2):407-416.
6JH,Shaw DW,et al.Agreement among evaluators of bovine embryos produced in vitro or in vivo[J].Biol Reprod.1995,52(3):676-682.