Effects of 25-hydroxyvitamin D₃ and manipulated dietary cation-anion difference on the tenderness of beef from cull native Korean cows

In this study, we characterized the effects of 25-hydroxyvitamin D₃ (25-OH D₃) and manipulated dietary cation-anion difference (DCAD) on the performance, urine pH, serum constituents, carcass traits, tissue residual vitamin D and its metabolites, beef tenderness, and mRNA and protein concentrations of Ca-dependent proteinases in LM using 24 cull native Korean cows. The cows were divided into 3 groups of 8: control, 25-OH D₃ supplemented (25-OH D₃), and manipulated DCAD plus 25-OH D₃ supplemented (DCAD+25-OH D₃). Cows receiving 25-OH D₃ or DCAD+25-OH D₃ were dosed with 125 mg of 25-OH D₃ 6 d before slaughter. The manipulated DCAD (-10 mEq/ 100 g of DM) diet was fed from 20 to 6 d (14 d) before slaughter. The DCAD+25-OH D₃ treatment decreased urine pH and increased serum Ca concentrations. Although the vitamin D concentrations in LM, liver, and kidney were not affected by 25-OH D₃ or DCAD+25-OH D₃, muscle tissue 25-OH D₃ concentrations were increased by both regimens. Serum 25-OH D₃ concentrations were increased by 25-OH D₃ supplementation, and the increase was even greater for DCAD+25-OH D₃. The same pattern was observed for serum 1,25- (OH)₂ D₃. However, the LM concentration of 1,25-(OH)₂ D₃ was less for DCAD+25-OH D₃ than for control. Although Ca concentrations of LM increased numerically in response to 25-OH D₃ supplementation, no statistical differences in Warner-Bratzler shear force or sensory traits of LM were detected. The LM of cows receiving 25-OH D₃ with or without manipulated DCAD had greater concentrations of μ-calpain and m-calpain mRNA, whereas the reverse was observed for calpastatin mRNA. Expression of μ-calpain protein was increased relative to control by DCAD+25-OH D₃. The amount of 25-OH D₃ and manipulated DCAD administered to cull native Korean cows was insufficient to improve tenderness of beef by increasing muscle Ca concentration. However, DCAD+25-OH D₃ induced greater expressions of μ-calpain protein as well as mRNA.