Genetic (co) variance for growth and tenderness related traits in purebred Brahman steers

Paternal half-sib groups of Brahman bull calves were purchased at weaning from purebred Brahman producers in Louisiana. Following backgrounding and grazing on ryegrass the steers shipped to a commercial feedlot in south Texas. Steers were slaughtered in groups when they reached an approximate average endpoint weight of 535 kg and 10mm backfat. After a 24 hr chill, carcasses were ribbed, data collected, and a longissimus muscle sample taken for calpastatin assay. Two 2.54 cm thick steaks were randomly removed from the large end of the strip loin, vacuum packaged, and randomly selected for 7 and 14 days of aging. Genetic correlations and heritabilities were calculated with an animal model using MTDFREML. The means were 1.49 kg/d for ADG, 336.4kg for USDA yield grade, 58.7 cm2 for ribeye area, 0.87 cm for fat thickness, 2.12 for percent kph, 2.34 for USDA yield grade, and 390.3 for marbling score which equals a high select USDA quality grade. Other means were 10.60 and 10.59 for purge loss after 7 and 14 days aging, 21.07 and 21.56 for percent cooking loss, 4.57 and 3.85 kg for shear force after 7 and 14 days aging. Factors influencing shear force were marbling score, purge loss after 7 day aging, purge loss after 14 day aging, cook loss after 7 day aging, cook loss after 14 day aging, and calpastatin. Heritablilities for growth and carcass traits were similar to those of non-Brahman cattle. Heritabilities for cooking traits were low. Tenderness as affected by moisture loss during the thawing and cooking process needs to be studied further