Quantitative and molecular genetic influences on properties of beef: a review

The scientific literature is reviewed to identify quantitative and molecula r genetic influences on quantity and quality of beef. Genetic variation bet ween breeds is of similar magnitude to genetic variation within breeds for many economically important traits. Differences between breeds are signific ant and large for most carcass and beef quality attributes, including beef tenderness, although differences for sensory juiciness and flavour are of l ittle practical importance. For traits such as beef tenderness, between-bre ed differences may be more easily exploited than within-breed differences, because exceptional breeds are easier to identify than exceptional animals. Effects of heterosis on carcass and beef quality attributes are relatively small (3% or less), with most effects mediated through heterotic effects o n weight. Carcass composition traits (e.g. carcass weight, fat thickness an d marbling) are moderately to highly heritable. Most estimates of retail be ef yield percentage are highly heritable, offering good potential for withi n-breed selection for the trait, although a moderate to strong antagonistic relationship exists between yield and marbling. This relationship needs to be considered in within-breed selection programs for yield percentage. Ear ly estimates of heritability of objective measures of beef tenderness (Warn er Bratzler shear force values) indicated tenderness was moderately to high ly heritable. Recent estimates using larger numbers of carcasses and more d iscriminatory methods of analysis indicate that beef tenderness is lowly he ritable in Bos taurus breeds and moderately heritable in Bos indicus and Bo s indicus-derived breeds. Within breeds, measures of 24-h calpastatin activ ity are genetically strongly correlated with shear force values but are mor e heritable. However, phenotypic correlations between shear force values an d 24-h calpastatin activities are low. There are also inconsistencies in re lationships between these measurements across breeds. Low correlations betw een tenderness in different muscles, low to moderate heritabilities and inc onsistent variation within- and between-breeds for traits such as 24-h calp astatin activity suggest that genetic improvement in beef tenderness may be difficult. The possibility exists that significant mitochondrial genetic e ffects occur for some carcass and beef quality attributes. A major gene for muscular hypertrophy in cattle significantly affects carcass and beef qual ity characteristics. Genome-wide screening of DNA markers indicates a numbe r of putative Quantitative Trait Loci (QTL) associated with carcass and mea t quality characteristics. Published data for these QTL are summarised. Str ategies to combine quantitative and molecular genetic information to maximi se genetic progress are discussed.