Response to ten generations of index selection for components of litter size in swine

Casey, D.; Rathje, T. A.; Johnson, R. K.

A line of pigs that had been selected for 10 generations on an index for increased ovulation rate and embryonic survival at 50 days of gestation and a randombred control line were studied. Selection was based on dam's index, and in each generation 40 of 160 and 15 of 160 were selected. Laparatomy was performed at 50 days of gestation and the index was calculated from counts of corpora lutea and fetuses. The index was constructed to maximize the number of fetuses.