Vitamin D-3 supplementation of beef steers increases longissimus tenderness

The objectives of these experiments were to determine 1) the effectiveness of supplement;al vitamin D-3 (VITD) on altering plasma and muscle calcium l evels, 2) whether VITD supplementation improves Warner-Bratzler shear force (WBS) values of steaks from. feedlot beef steers, and 3) the tenderness re sponse curve of longissimus steaks from steers supplemented with VITD. In E xp. 1, 20 crossbred steers were assigned randomly to one of four treatment diets: consisting of either 0, 2.5, 5.0, or 7.5 x 10(6) IU of VITD per day for 10 d. Blood samples were obtained daily during this supplementation per iod and 5 d thereafter (d 11 to 15). Between d 6 and 13, a linear increase (P < .01) in ionized plasma calcium concentrations was observed in steers s upplemented with VITD. Compared to unsupplemented steers, serum calcium con centrations of the steers receiving 7.5 x 10(6) IU of VITD per day were inc reased 8 to 48%. In Exp. 2, longissimus samples from crossbred steers (n = 118) that were supplemented with either 0 or 5 x 10(6) IU of VITD per day f or 7 d were obtained and aged for 7, 14, or 21 d. Following the initial 7-d postmortem aging period, VITD supplementation lowered (P < .01) WBS (.58 k g) and increased sensory tenderness rating (.6 units) compared to cuts orig inating from unsupplemented steers. In Exp. 3, 44 steers were supplemented with either 0 or 7.5 x 10(6) IU of VITD per day for 10 d immediately prior to slaughter.; Results indicated that plasma and longissimus calcium concen tration were higher (P < .05) for steers that received supplemental VITD. C ompared with unsupplemented cuts, VITD supplementation improved WBS of cuts aged for either 7 or 14 d (P = .02 and P = .07, respectively). Sensory pan elists rated samples from VITD supplemented steers as more tender than thei r unsupplemented counterparts. Activation of calpain proteases could be res ponsible for the observed tenderization due to the supplementation of VITD.