Relative Tissue Growth Patterns and Carcass Composition in Beef Cattle

Abstract

Summary The main objective of the beef breed evaluation programme carried out at Grange Beef Research Centre was to compare the productive characteristics of different beef breed crosses out of Holstein-Friesian cows. In the course of this work much additional information was acquired, particularly on growth patterns of body organs and tissues, and how these affect kill-out proportion and carcass composition. The data were also used to examine relationships between carcass classification variables and carcass composition. Cattle used for beef production in Ireland can be classified into three main biological types: (i) early maturing, (ii) dairy, and (iii) late maturing. Results from an experiment that compared Friesians (dairy), Hereford × Friesians (early maturing) and Charolais × Friesians (late maturing) are used to represent these biological types. The material is organized under the following headings: (i) non carcass parts and kill-out proportion, (ii) carcass composition, (iii) carcass tissue distribution, (iv) muscle chemical composition, (v) gender, (vi) dairy breeds, and (vii)carcass classification and composition. Kill-out proportion increased by about 10 g/kg from Friesians to Hereford × Friesians to Charolais × Friesians. It also increased by about 10 g/kg per 100 kg increase in slaughter weight. Friesians had higher proportions of gastrointestinal tract plus contents than the two beef crosses and also had higher proportions of metabolic organs. Hereford crosses had a higher proportion of hide and offal fats than Charolais crosses. At any carcass weight, early maturing animals had more fat and less bone and muscle than late maturing animals. As carcass weight increased, the proportions of bone and muscle in the carcass decreased, and the proportion of fat increased, but the rates of these changes differed with biological type. Carcass muscle distribution also differed with biological type. Late maturing cattle had a higher proportion of hind quarter and higher value muscle than Friesians and early maturing animals, while Friesians had higher proportions than early maturing animals. Muscle lipid content (marbling) differed with biological type (early maturing > dairy > late maturing) and with carcass joint (highest for flank and ribs, lowest for m. longissimus). Early maturing steers and heifers had similar carcass fat proportions when the heifers were about 60 kg carcass lighter than the steers. Despite having poorer carcass conformation, heifers had a slightly higher proportion of muscle and a considerably higher proportion of higher value muscle than steers. Carcass classification grade was not a reliable indicator of carcass muscle proportion. Carcass fat class was related to both carcass fat and muscle proportions but accounted for less than half the variance in these. Carcass conformation class was not related to carcass fat proportion, carcass muscle proportion or higher value muscle proportion, but it was negatively related to carcass bone proportion.