The improvement of beef tenderness is related to the degradation of myofibrillar proteins due to the release of the protease μ-calpain by calcium. The relationship of Calcium and Vitamin D3 allows for the theory that the oral supplementation of Vitamin D3 will increase the calcium content in muscles resulting in an increase in the protease μ-calpain resulting in increased tenderness. A study to investigate the effect of feeding Vitamin D3 prior to cattle harvest on tenderness of muscles from different biological types of cattle was conducted at Texas Tech University. Bos Tauras-continental, Bos Tauras-english and Bos Indicus feedlot steers were fed four different levels of Vitamin D3 for eight consecutive days. Feedlot performance data-carcass data were collected and shear force analysis was conducted at days 3, 7, 10, 14 and 21. Biological type of cattle did not affect Vitamin D3 treatment for any carcass, feedlot performance or tenderness traits measured. In turn, feeding Vitamin D3 before harvest will affect all cattle in a similar fashion. Supplementing steers with ½ million IU's/head/day for eight consecutive days improved the shear force in the longissimus lumborum and semimembranosus steaks by affecting the calcium and μ-calpain, while having only a minor effect on tissue Vitamin D concentrations, and no adverse effects on feedlot performance.