-A selection experiment was conducted over six generations in a purebred French Large White population presumably free of the HAL" and RN-alleles. Two lines were taken from the same base population and were contemporarily bred: one control line (C) and one line (S) (-0, 42 ! 0, 12

-A selection experiment was conducted over six generations in a purebred French Large White population presumably free of the HAL" and RN-alleles. Two lines were taken from the same base population and were contemporarily bred: one control line (C) and one line (S) (-0, 42 ! 0, 12

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' and RNalleles. 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 firstparity 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 (1084 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 * Correspondence and reprints: Station d'amelioration génétique des animaux, BP 27,

A six-generation selection experiment comprising a selected (S) and a control (C) line has been conducted with the objective of decreasing muscle glycolytic potential in purebred French Large White pigs. Both lines consisted of six to eight sires and about 40 dams per generation, and each dam produced two litters. The selection criterion in the line S was the in vivo glycolytic potential (IVGP) of the Longissimus (ld) muscle, measured on a shot-biopsy sample removed at 75 kg live weight on boars and gilts from first-parity litters. In addition, the post mortem glycolytic potential (PMGP) of ld, semime!n6ranosus (sm) and semispinalis capitis (sc) muscles was recorded on pigs from second-parity litters slaughtered at 100 kg live weight. Throughout the experiment, 2 981 and 454 animals were recorded for IVGP and PMGP, respectively. A consistent decrease in IVGP and, to a lesser extent, in PMGP was obtained in the line S compared with the line C. Estimates of genetic changes per generation were -0.18, -0.11, -0.07 and -0.09 SD units of the trait for IVGP and PMGP of ld, sm and sc muscles, respectively. The REML heritability estimates were 0.25 ! 0.02, 0.15 f 0.06, 0.14 ± 0.06 and 0.17 ! 0.05 for the above four traits, respectively. The REML estimate of genetic correlation of IVGP with PMGP ld (0.87 f 0.15) was somewhat higher than those of IVGP with PMGP of sm and sc (0.56 iL 0.14 and 0.68 t 0.13, respectively). It is concluded that downward selection on muscle glycolytic potential may be effective in pigs. © Inra/Elsevier, Paris pig / muscle glycolytic potential / selection experiment / genetic parameters

-A six-generation selection experiment comprising a selected (S) and a control line (C), and aiming at decreasing muscle