Data for 15 487 pigs taken from the first 8 years (1973–81) of the Meat and Livestock Commission's Commercial Pig Evaluation were used to examine the effects of sex, feeding regimen, slaughter weight and day of slaughter on muscle quality characteristics in 20 populations (pigs from different commercial breeding companies and control populations). The characteristics examined included pH measurements both at 45 min post mortem (pH,) and after overnight cooling (pH2), in the m. longissimus and m. semimembranosus. Visual assessments of m. longissimus colour and condition were also made.
The overall mean for pH, in the m. longissimus was 6·34; 0·12 of pH, values were less than 6·0. The proportion of carcasses visually assessed as either pale or wet was 0·116, and 0·027 were assessed as both pale and wet.
The populations were compared separately within each of three time periods (covering the full 8 years) since significant population × time period interactions were recorded for several characteristics. Within each period the populations differed significantly for all characteristics examined (P < 0·05); but with the exception of two extreme populations, the differences were relatively unimportant.
The effects of sex, feeding regimen and slaughter weight were negligible but the effect of day of slaughter was very important: the s.d. of pH1 was reduced by 0·15 when calculated within day but by only 0·01 when adjusted for all other factors.
Muscle quality characteristics were poorly correlated with carcass characteristics: the highest correlation within day of slaughter was −0·23, recorded between pH, and ham conformation score.