The effects of sex and slaughter weight on muscle fibre characteristics and physico-chemical properties of lamb longissimus thoracis muscle

The objective was to investigate the effect of sex and slaughter weight on muscle fibre and meat quality traits of longissimus thoracis (LT) muscle in lambs. Used were 22 female and 30 male lambs of Polish Longwool sheep from two slaughter weight groups: I – 15-20 kg and II – 25-30 kg. LT muscle samples were taken to categorize fibre types (I, IIA and IIB) according to their NADHtetrazolium reductase activity and to determine the pH24, colour L*a*b*, drip loss, thermal loss, and Warner-Bratzler shear force of meat. Fibre type percentage, fibre diameter and phenotypic correlation between fibre traits and meat quality traits were estimated. Sex and slaughter weight had no effect on muscle fibre types percentage, but affected the diameter of fibres. Likewise, pH24, drip loss and thermal loss were not affected by these two factors. On the other hand, in males compared to females and with increasing slaughter weight, meat lightness decreased, whereas shear force values and diameter of muscle fibres increased. The phenotypic correlations between histological and meat quality traits were generally low. The percentage of type I, unlike that of type IIB fibres, positively correlated with meat pH24 and shear force, while negatively with meat lightness. Meat yellowness was positively related to percentage of type IIB fibres. A trend was found between redness and percentage of type I fibres. Moreover, increased diameter of type IIB fibres was found to be related to the increased shear force values.