2CHRISTOPHER J Y, JAKOB U, BRIDGET L, et al, Age specific fecundity,litter size, and sex ratio in the Chaeoan Peooary [ J ]. Zoo Biology, 1997,16 : 301 - 307.
3PERE M C, ETIENNE. Uterine blood flow in sows effects of pregnancy stage and litter size[ J]. Reprod Nutr,2000 ,40 :369 - 382.
4VALLET J L, CHRISTENSON R K. Effect of progesterone, mifepristone and estrogen treatment durtin early pregnancy on conceptus development and uterine capacity in swine [J]. B iol Reprod ,2004,70: 92 - 98 (015).
