Abstract: In order to explore the effect of different parity， birth month and backfat thickness（BF） on reproductive performance in sows， a total of 3 972 reproductive records of Landrace×Yorkshire （LY）sows from a Fujian farm were analyzed and 508 sows（LY） in different stages were selected for backfat thickness determination. The results showed that the reproductive performance from 3th to 6th parities were better than that of other parities. The total number born（TNB）， birth weight（BW） of 1st parity was significantly lower than those of 2nd to 7th parities（P<0.05）， the number born alive（NBA） was significantly less than those of 2nd to 6th parities（P<0.05）. The TNB， NBA was higher in February， March and May, but lower in January， November and December. The number of stillbirth in July and August was higher than others. The TNB and NBA were higher in the group with BF from 18 mm to 20 mm at mating compared with from ≥ 21 mm group （P<0.05）. There was no difference in TNB and NBA among each BF groups of weaned sows （P>0.05）. Before farrowing， BF of 20-23mm groups performed significantly higher TNB and NBA than the 10-15 mm group （P<0.05）， and BF ≥ 24 mm has the highest stillbirth proportion which was up to 58%.Besides， the back fat losses between 4-6 mm during lactation had the shortest estrus interval， which was significantly lower than fat loss >6 mm group （P<0.05） and <0 mm group （P<0.05）. The study showed that parity， birth month， backfat thickness had significant effect on reproductive performance of sows.

Key words: parity, birth month, backfat thickness, reproductive performance