[Effect of population size of performance test on short-term selection result of sire line].

The effects of the population size,boar to sow ratio,and the number of pigs tested per litter on the selection response and its coefficient of variation, inbreeding coefficient of sire line selection were studied. Pig populations of 100 to 500 sows were simulated with Monte Carlo method,and the ratios of boar to sow were 1:10 and 1:20. The number of pigs tested per litter were 2 and 4 composed equally of boars and gilts. The traits selected were average daily gain after weaning (ADG) and backfat thickness (BF) at 100 kg live weight. Breeding pigs were selected according to multiple-trait BLUP,and economic weight of BF was set as 2.5 times of that of ADG. After five generation selection, the results showed that the more the number of sows of the breeding population, the higher the cumulative selection response at 5th generation, and the slower the coefficient of inbreeding increment per generation, the smaller the coefficient of variation of the cumulative selection response at 5th generation. Increasing the number of pigs tested per litter and/or the boar to sow ratio increased the cumulative selection response at 5th generation, inbreeding coefficient increment per generation, and the coefficient of variation of the cumulative selection response at 5th generation. The cumulative selection response got higher and the increment of inbreeding coefficient slowed down significantly when the number of sows in the breeding population increased from 100 to 300,and the ratio of boar to sow and the number of pigs tested per litter were fixed. When the sow number of breeding population was increased from 300 to 400 above,the cumulative selection response only increased slightly,and the coefficient of inbreeding continued to decrease but at a diminished rate. In conclusion, for the short-term selection of sire line, it is recommended that the breeding population should be composed of 400 or above sows, 4 pigs tested per litter,and the ratio of boar to sow should be maintained at 1:20.