Intra-Uterine Migration and Embryonic Death in Swine

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Abstract
A total of 119 crossbred gilts was bred and slaughtered when each of them approached the 55th day of pregnancy. At slaughter the number of corpora lutea on each ovary and the number of embryos present in each uterine horn were recorded. Intra-uterine migration, as determined when the number of embryos in any one uterine horn exceeded the number of corpora lutea on the corresponding ovary, was observed in 41.2% of the gilts. The total ovulation rate of both ovaries did not seem to be related to the occurrence of intra-uterine migration. However, an unequal ovulation rate between the ovaries of the same gilt was related to the occurrence of this phenomenon. Intra-uterine migration of the fertilized ova was from the left to the right uterine horn in 69% of the cases. This was due to the production of 1.32 more ova by the left ovary. In spite of this unequal production of ova by the ovaries, the embryos were equally divided between the uterine horns at the 55th day of gestation. Litters contained 1.24 more pigs where intra-uterine migration was observed and 1.73 fewer corpora lutea not represented by embryos where intra-uterine migration was not observed. This suggests the possibility that intra-uterine migration may be important in preventing embryonic death losses, probably because of equal distribution of embryos between the uterine horns. No evidence was obtained which indicated that intra-uterine migration of fertilized ova had a genetic basis, since differences between sire groups and crossbred groups were not significant. Copyright © 1963. American Society of Animal Science . Copyright 1963 by American Society of Animal Science

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