Abstract
The data on reproductive performance of 1065 purebred Landrace, 1254 purebred Yorkshire. 553 purebred Duroc and 327 purebred Pietrain sows bred to farrow purebred litters and data from 3413 Landrace $\times$ Yorkshire, 487 Duroc $\times$ Pietrain and 3191 commericial litters were udsed in this study. The data were collected form litters farrowed form January 1986 to December 1988 in Holiday Hills Stock and Breeding Farms, San Prero, Laguna. The crossbred sows and litters were better in most traits associated with sow productivity than their contemporary purebred sows and litters. The Duroc $\times$ Pietrain crossbred litters showed 16.67% improvement in litter size at weaning, 10.11% improvement in survival rate form birth to weaning and 16.21% more pigs per sow pre year than the averages of their parental breeds. The litters from the Landrace $\times$ Yorkshire crossbred sows sired by either Duroc or Duroc $\times$ Pietrain boars had 11.01% bigger litter size at birth, 20.74% increase in litter size at weaning and 22.86% more pigs weaned per sow per year than the averages of the four parental breeds. Very little improvement in most traits evaluated were observed form the Landrace $\times$ Yorkshire crossbred litters compared with their parental breeds. Year of birth of litter had litter influence on sow productivity. However, the reproductivity performance declined when sows farrowed in June up to September. The best Months of farrowing were found to be from January to April. The breed $\times$ year, breed $\times$ month and year $\times$ month had no significant effects on all traits evaluated.