Effect of Number of Embryos on Embryonic Survival in Recipient Gilts

ESTRUS was synchronized in 36 crossbred gilts by feeding methallibure for 20 days followed by PMS and HCG treatment to control the time of ovulation. At 24°4 hr. after ovulation, eggs were recovered surgically from the donor gilts and either 12 or 24 ova were transferred to the oviducts of non-mated recipient gilts. Of the 332 ova transferred, 68.4% were at the two-cell stage of development and the remainder were either single-cell (21.1%) or four-cell ova (10.5%). Average litter size at 25 days of gestation in gilts receiving 24 ova was significantly higher (P<.01) than that in gilts receiving 12 ova. Nine of the 10 recipient gilts to which 24 ova were transferred had from 14 to 23 normal embryos per litter at slaughter. The results of this study agree with the idea that overcrowding is not a major factor limiting litter size in swine during the first 25 days of pregnancy.