Selection for reduced muscle glycolytic potential in Large White pigs. I. Direct responses

A six-generation selection experiment comprising a selected (S) and a contr ol (C) line has been conducted with the objective of decreasing muscle glyc olytic potential in purebred French Large White pigs. Both lines consisted of six to eight sires and about 40 darns per generation, and each dam produ ced two litters. The selection criterion in the line S was the in vivo glyc olytic potential (IVGP) of the longissimus (Id) muscle, measured on a shot- biopsy sample removed at 75 kg live weight on boars and gilts from first-pa rity litters. In addition, the post mortem glycolytic potential (PMGP) of I d, semimembranosus (sm) and semispinalis capitis (sc) muscles was recorded on pigs from second-parity litters slaughtered at 100 kg live weight. Throu ghout the experiment, 2981 and 454 animals were recorded for IVGP and PMGP, respectively. A consistent decrease in IVGP and, to a lesser extent, in PM GP was obtained in the line S compared with the line C. Estimates of geneti c changes per generation were -0.18, -0.11, -0.07 and -0.09 SD units of the trait for IVGP and PMGP of Id, sm and sc muscles, respectively. The REML h eritability estimates were 0.25 +/- 0.02, 0.15 +/- 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 Id (0.87 +/- 0.15) was somewhat high er than those of IVGP with PMGP of sm and sc (0.56 +/- 0.14 and 0.68 +/- 0. 13, respectively). It is concluded that downward selection on muscle glycol ytic potential may be effective in pigs. (C) Inra/Elsevier, Paris.