COMPARATIVE REPRODUCTIVE-PERFORMANCE IN MEISHAN AND LARGE WHITE-PIGS AND THEIR CROSSES

A crossbreeding trial extending over three generations was used to inv estigate the genetic components contributing to the prolificacy of the Meishan breed in comparison with the Large White breed. Information o n the number of teats and on body weight and litter size in the first two parities was recorded an purebred Meishan and Large White females and on reciprocal F-1 and backcross females. Ovulation rate was also r ecorded for all litters, allowing the estimation of per litter prenata l survival. Crossbreeding parameters for direct, maternal and grandmat ernal effects were estimated using restricted maximum likelihood analy sis. There was a consistent advantage of three to four piglets born al ive to the Meishan female compared with the Large White female. This w as controlled by the maternal genotype, with no effect of the genotype of the litter itself. Both additive and heterosis effects were import ant, the contribution ofadditive maternal effects to the breed differe nce being similar across parities (4.0 (s.e. 1.1) and 4.2 (s.e. 1.1), in the two parities respectively) and the maternal heterosis increasin g slightly across parities (2.2 (s.e. 0.8) and 2.9 (s.e. 0.8), in the two parities respectively). The number born alive to F-1 females was s imilar to, or greater than, the number born alive to Meishan females. Ovulation rate was significantly higher in Meishan than in Large White females and this was controlled by aditive gene effects which had a s imilar effect across parities, the weighted average of their contribut ion to the breed difference being 5.7 (s.e. 0.8) ova. Differences betw een the breeds in prenatal survival were small, although there was sig nificant maternal heterosis, however, the maternal additive effect bec ame significant after the inclusion of ovulation rate as a covariate. After adjustment for ovulation rate, the weighted average estimates ac ross parity of the maternal additive contribution to the breed differe nce and the maternal heterosis for the proportional prenatal survival were 0.14 (s.e. 0.05) and 0.13 (s.e. 0.03), respectively. This suggest s that a combination of a high ovulation rate and especially 8 high le vel of prenatal survival for that ovulation rate led to the prolificac y observed in this sample of Meishan pigs. The inclusion of ovulation rate as a covariate in the analysis of number born alive confirms this view, as the maternal additive effect on litter size colts only reduc ed by about one third and the heterosis effect was largely unchanged. Both ntrmbeus stillborn and mummified were increased in litters born t o Meishan sows due to maternal additive effects, but the effects seeme d largely a consequence of the increased ovulation rate as they became non-significant after its inclusion as a covariate in the model.