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

A six-generation selection experiment comprising a selected (S) and a control line (C), and aiming at decreasing muscle glycolytic potential has been conducted in purebred Large White pigs presumably free of the Hal(n) and RN- alleles. Both lines consisted of six to eight sires and around 40 dams per generation. Each dam produced two litters with replacement boars and gilts kept 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 about 75 kg live weight. Correlated responses to selection for low IVGP as well as heritabilities and genetic correlations with IVGP were estimated for average daily gain (6 761 offspring from parities 1 and 2), ultrasonic backfat thickness (3 078 boars and gilts from parity 1), carcass composition traits (1 185 castrated males and gilts from parity 2), age at first oestrus (1 084 gilts) and litter size and weight at birth, at 21 days of age and at weaning (917 litters). Heritability estimates of these traits were within the usual range of literature values. The estimates of genetic correlation (r(A)) with IVGP were 0.15 +/- 0.07 for average daily gain, -0.32 +/- 0.06 for ultrasonic backfat thickness, -0.20 +/- 0.10 for carcass 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 r(A) estimates pertaining to carcass composition traits, the most pronounced correlated response to downward selection on IVGP was a decrease of carcass lean to fat ratio in the S line compared with the C line. Genetic treads per generation amounted to -0.13, 0.12 and 0.16 phenotypic standard deviation units of lean meat percentage, backfat thickness and backfat weight, respectively. A negative r(A) 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 or noticeable correlated genetic trends in the S line, regarding litter size and weight traits. (C) Inra/Elsevier, Paris.