Abstract:  To further understand the reproduction traits of sows and provide reference for pig breeding， 9720 records of gestation length （GL） for Duroc， Landrace and Large White sows from a pig farm during 2005 to 2013 in Zhejiang Province were analyzed. The results indicated that variety， pedigree， farrowing season and year， fetal parity had highly significant effects on gestation length （P<001）. Among different varieties， Landrace had the longest average gestation length of 11653 d， followed by 11417 d in Yorkshire and 11352 d in Duroc. Sows which gave birth to piglets in warm temperature season from June to November had the shortest gestation length in Zhejiang Province. In the first three parities， sows had the longest gestation length at primiparity， and shortest at the second parity. The gestation length was significantly influenced by paternal pedigrees for 125 d difference in Duroc. In recent years， gestation length had a gradual shortening trend in Duroc， Landrace and Large White sows.

Key words: pig, gestation length, influence factor