Selection for reduced muscle glycolytic potential in Large White pigs. III. Correlated responses in growth rate, carcass composition and reproductive traits.

摘要

A 6-generation selection experiment using a selected (S) and a control line (C), with the aim of decreasing muscle glycolytic potential, was conducted in Large White pigs that were presumed to lack the Haln and RN- alleles. Both lines consisted of 6-8 sires and～40 dams per generation. Each dam produced 2 litters, and replacement boars and gilts were retained from the first-parity litters. The selection criterion in the S line was the in vivo glycolytic potential (IVGP) of the longissimus muscle, measured on a shot biopsy sample removed at a live weight of～75 kg. Correlated responses to selection for low IVGP as well as heritabilities and genetic correlations with IVGP were estimated for average daily gain (6761 offspring from parities 1 and 2),ultrasonic backfat thickness (3078 boars and gilts from parity 1), carcass composition traits (1185 castrated males and gilts from parity 2), age at first oestrus (1084 gilts) and litter size and weight at birth, 21 days of age and weaning (917 litters).Heritability estimates of these traits were within the usual range of values found in the literature. The estimates of genetic correlation (rA) with IVGP were 0.15±0.07 for average daily gain, -0.32±0.06 for ultrasonic backfat thickness, -0.20±0.10 forcarcass backfat thickness, -0.24±0.09 for weight of backfat, 0.18±0.09 for carcass lean meat percentage, and 0.49±0.15 for loin muscle area. In agreement with the rA estimates for carcass composition traits, the most pronounced correlated response to downward selection on IVGP was a decrease in the carcass lean:fat ratio in the S line compared with the C line. Genetic trends per generation were -0.13, 0.12 and 0.16 phenotypic standard deviation units of lean meat percentage, backfat thickness and backfat weight respectively. A negative rA estimate (-0.29±0.11) was found between age at first oestrus and IVGP, but there was no evidence for significant genetic relationships with IVGP and no noticeable correlated genetic trend in the S line with respect tolitter size and weight traits.