The same trial also showed that one bull produced very good amounts of meat in the progeny, but the meat was very tough. So there is variability within a breed. Again, in the USA, the Brahman breed is considered to lack meat tenderness. When investigated, it was found that different Brahman breeding bulls gave calves with different muscle tenderness - with the mean values by sire ranging from 5.3 to 6.8 kg in the shear test. Double muscled' breeds have been shown to have meat as tender as standard European breeds - and for a number of cuts it is more tender.
Tenderness is heritable.
In sheep there are breed differences in the pH of muscles. Coopworth meat has tested at pH 5.77 and purebred Merinos at pH 6.16. Cross breds tend to be intermediate, as you would expect. Again, there is a degree of heritability of tenderness. But even the most tender meat derived from progeny of the most select of sires can be ruined by stress before slaughter.