Effect of rate of pH decline on muscle enzyme activities in two pig lines

Muscle enzyme activities were measured in In. transversus abdominis (TA) sa mples of two pig lines, differing in stress sensitivity and in breeding obj ectives. Animals of line one were stress sensitive and selected for a high carcass lean content (LEAN), those of line two were homozygous stress resis tant and selected for maximum live weight gain (GROWTH). Muscle samples of 16 pigs per line were excised at 1 h and sampled at 3 h post mortem. Boars, gilts and barrows were almost equally represented. Pigs of line GROWTH had a higher fat and lean tissue gain (P < 0.01) and a lower carcass lean cont ent (P < 0.001) than those of line LEAN. Lower activities of mu -calpain, m -calpain, pyroglutamyl aminopeptidase I, acid lipase and neutral phospholip ase were measured in TA muscle samples of line LEAN compared with line GROW TH (P < 0.05). Activities of dipeptidyl peptidase IV and acid phospholipase tended to be somewhat lower for line LEAN, whereas activities of calpastat in, cathepsin (B + L) and cathepsin D were not different. Sex-class effects were analogous to line effects. Significant correlation coefficients betwe en activities of several enzymes and pH values 1 h post mortem, both within and across lines, suggest that lower enzyme activities are a consequence o f a more pronounced denaturation due to a faster post mortem pH decline. (C ) 2000 Elsevier Science Ltd. All rights reserved.