Production factors influence fresh lamb longissimus colour more than muscle traits such as myoglobin concentration and pH

• Site of production and slaughter group had the greatest effect on meat L*, a* and b*.
• Increasing muscle myoglobin concentration reduced meat L* more than increasing pH24.
• Reducing meat pH24 increased loin a* more than increasing myoglobin concentration.
• Increasing myoglobin accounts for reduced meat L* as lambs age from 140 to 400 days.

M. longissimus colour was measured from 8165 lambs at 24 h post-mortem using a chromameter. The impact of production factors (site and year of production, slaughter group, sex, age and breed type) and muscle traits (hot carcass weight, pH24, isocitrate dehydrogenase (ICDH) activity, myoglobin, iron and zinc concentrations) on meat lightness (L*), redness (a*), yellowness (b*), hue and chroma were analysed. Greater differences in meat colour were seen between different slaughter groups and sites of production than across the range of any muscle traits. Of the muscle traits analysed, changes in pH24 had the greatest effect on meat a* (2.5 units), while myoglobin had the greatest effect on meat L* (2.9 units). The 3.1 L* unit darkening of meat with increasing lamb age (from 140 to 400 days) was accounted for by increased myoglobin concentration. These results suggest that production factors are having substantial effects on lamb colour independent of known influencing muscle traits such as myoglobin concentration and pH.