Abstract: This experiment was aimed to reveal the effects of sows’ backfat thickness at farrowing and at weaning on reproductive performance. The backfat thickness at farrowing and at weaning was determined by type-A ultrasonic device. According to the backfat thickness at farrowing, sows were divided into group 1 （<10 mm）, group 2 （10～14 mm）,group 3 （>14 mm）;According to the backfat thickness at weaning, sows were divided into group A （<7 mm）, group B （7～10 mm）, group C （10～13 mm）,group D （13～16 mm）,group E （>16 mm）；According to the loss of backfat thickness during the lactation period, sows were divided into group Ⅰ（<3 mm），group Ⅱ（3～6 mm） and group Ⅲ（>6 mm）. The results showed that the rate of sows producing stillbirth was 10.5% in group 2, which was the least in the three groups, and the average weaning-estrus interval of group C was significantly shorter than other groups （P<0.05）. During the lactation period, the loss of back fat thickness in group Ⅲ was higher than groupⅠand groupⅡevidently, and the average estrus interval of group C was also markedly higher than groupⅠand groupⅡ （P<0.05）. The study indicated that sows with medium backfat thickness at farrowing and weaning shown the best reproduction performance. And an regression equation was established to forecast estrus date based on backfat thickness at weaning: Y=31.787－6.169X＋0.440X²－0.009X³.

Key words:

backfat thickness; estrus interval; loss of backfat thickness; reproductive performance; sows