In Trial 1, rams (n=26) were fed different levels (0, 250,000, 500,000 or 750,000 IU) of vitamin D(3) for 4 days to determine the most effective dose to increase blood calcium concentrations. Trial 2 consisted of feeding feedlot lambs (n=40) different levels (0 or 750,000 IU) of vitamin D(3) for 14 days to determine if vitamin D(3) could improve the tenderness of lamb muscles. Lambs were slaughtered and the M. longissimus lumborum, M. biceps femoris, M. semitendinosus, and M. semimembranosus were removed after chilling, cut into chops, and assigned to an aging period (5, 10 or 15 days) for Warner-Bratzler shear force (WBS) determination. In Trial 1, feed intake and weight gain were lower for rams supplemented with 500,000 IU of vitamin D(3) compared to all other groups. Blood calcium concentrations were not different between groups, although the 750,000 IU group tended (P<0.10) to have higher blood calcium concentrations on day 5 of the trial compared to controls. In Trial 2, blood calcium concentrations were not different between the treated and control groups, however, treated lambs had higher (P<0.01) calcium concentrations in both the liver and kidneys. Control chops from the M. longissimus lumborum had lower (P<0.05) WBS values than chops from vitamin D(3) fed lambs, but no other muscles were affected by vitamin D(3) feeding. An interaction between treatment and aging was observed for the M. biceps femoris, with chops from vitamin D(3) fed lambs having lower WBS values at 5 days aging, but chops from control lambs having lower WBS values at 15 days aging. WBS values decreased for the M. longissimus lumborum, M. semitendinosus, and M. semimembranosus with increasing aging time. Vitamin D(3) supplementation was not an effective means of improving the tenderness characteristics of lamb muscles.