Influence of early postweaning traits on genetic improvement of meat productivity in purebred Berkshire pigs

The objective of this study was to estimate genetic parameters for growth and body composition traits at 60 d of age and at finish in a population of Berkshire pigs and to evaluate the effectiveness of selection at 60 d of age for meat productivity. A total of 4,548 purebred Berkshire (2,344 males and 2,204 females) pigs born between December 1994 and January 2005 were used in this study. The traits analyzed were BW at 60 d of age; daily BW gain from birth to finish, from weaning to 60 d, from weaning to finish, and from 60 d to finish; age at finish; backfat thickness at 60 d of age and at finish; loin eye area at 60 d of age (LEA60) and at finish; and the number of teats. The heritability estimates for BW at 60 d of age, daily BW gain from weaning to 60 d, backfat thickness at 60 d of age, and LEA60 were 0.22, 0.25, 0.49, and 0.22, respectively. The estimated common environmental effect for BW at 60 d of age, daily BW gain from weaning to 60 d, backfat thickness at 60 d of age, and LEA60 were 0.12, 0.13, 0.18, and 0.21, respectively. Therefore, the common environmental effect should be included in the model to analyze traits at 60 d of age. The positive genetic correlation between LEA60 and loin eye area at finish and the negative genetic correlation between LEA60 and backfat thickness at finish indicated that improvement of the ultrasonic loin eye area at 60 d of age may result in favorable correlated responses to the traits at finish, an increase in loin eye area, and a decrease in backfat thickness. In addition, genetic correlations of backfat thickness at 60 d of age with backfat thickness at finish and loin eye area at finish were found to be favorable, indicating that improvement of ultrasonic backfat thickness at 60 d of age may result in greater correlated responses to the traits at finish: an increase in loin eye area and a decrease in backfat thickness. Therefore, constructing a selection scheme that includes body composition traits at 60 d and traits at finish is practical for gaining a greater selection response. Key words: Berkshire pig, genetic parameter, postweaning trait, teat number