CORRELATED RESPONSES OF CARCASS TRAITS TO SELECTION FOR MEET PRODUCTION PERFORMANCE IN LANDRACE PIGS

Abstract

Correlated responses of carcass traits to index selection for meet production performance were investigated of six generations of Landrace pigs and their genetic parameters were also estimated. A total of 141 boars and 136 castrated males were used by selecting one each of them from among 22 to 25 litters and 18 to 36 litters of each generation. The results examined on the basis of regression coefficients in terms of carcass lengths and back loin lengths revealed that the lengths of carcass, back loin I and back loin II became significantly shorter by 0.315cm (p<0.01), 0.333cm (p<0.05) and 0.324cm (p<0.01) per generation, respectively, whereas the length of loin eye did not change significantly. The lengths of cervical vertebra (A), thoracic vertebra from the 1st to the 5th (B) and the loin vertebra from the last lumber vertebra to pubic bone (D) were estimated on the basis of differences in the above-mentioned test results. The results suggested that the fore quarters of the carcass became shorter by selection for growth and backfat thickness. Also in the castrated males, the lengths of carcass and the back loin I became shorter by the selection by 0.638cm (p<0.01) and 0.431cm (p<0.01) per generation, respectively, and the length of tha back loin II also tended to become shorter. Although the live backfat thickness became thinner by 0.044cm per generation, the thickness of carcass backfat at shoulder, back, loin and the mean value showed hardly any changes. Genetic and phenotypic correlations between the carcass fat percentage and the live backfat thickness were found to be positive and higher than those between the fat percentage and the backfat thickness of carcasses. Genetic and phenotypic correlations between the fat percentage of carcass and the carcass traits in conjunction with length and eye muscle area were found negative. Converse relationship was found between the protein percentage of carcass and these traits as against the relation between the fat percentage of carcass and the traits.