Histological Profile of the Longissimus Dorsi Muscle in Polish Large White and Polish Landrace Pigs and its Effect on Loin Parameters and Intramuscular Fat Content*

The objective of this study was to analyse differences in individual fibre types in the histological profile of the longissimus dorsi muscle and their effect on pork carcass lean content and level of intramuscular fat (IMF) content, which determines palatability of meat and meat products. Analysis showed that the amount of type IIB fibres had a statistically significant (P<0.05) effect on the IMF content of the longissimus dorsi muscle. Animals with more than 70% of type IIB fibres in this muscle were also characterized by larger loin eye area (P<0.01) and loin eye height (P<0.05). Analogous relationships were noted when the analysed group of animals was divided according to the diameter of type IIA fibres. IMF was negatively correlated to the percentage of type IIB fibres (r_P= -0.162). Relationships with the other two fibre types were positive (IIA - r_P= 0.097; I - r_P= 0.187). It was found that increased percentage of type IIB fibres resulted in a slightly greater loin weight (r_P= 0.176), higher loin eye height (r_P= 0.136), larger loin eye area (r_P= 0.265) and higher carcass lean content (r_P= 0.204). Likewise, the increase in the number of type IIA and type I fibres decreased these parameters.