Feeding 25-hydroxyvitamin D 3 to improve beef tenderness 1 A. E. Wertz*, T. J. Knight*, A. Trenkle*, R. Sonon*, R. L. Horst†, E. J. Huff-Lonergan*, and D. C. Beitz* 2 *Department of Animal Science, Iowa State University, Ames 50011 and †National Animal Disease Center, USDA-ARS, Ames 50010 ABSTRACT: The objective of this trial was to deter- mine if a single oral bolus of 25-hydroxyvitamin D 3 (25- OH D 3 ) given at various times before slaughter would enhance the tenderness of beef loin steaks. One hun- dred eight crossbred steers were allotted to 18 pens so that the mean weight of the cattle in each pen was similar. Treatments (25-OH D 3 dose [62.5 or 125 mg]) and time of administration of the single oral bolus (4, 7, 21, or 35 d before slaughter) were assigned randomly to each pen of steers. Serial plasma samples were col- lected at each bolus administration time for control animals. For steers assigned to a treatment group, a baseline blood sample was collected before bolus admin- istration and at each subsequent administration when other treatment groups received their bolus. Plasma samples were assayed for 25-OH D 3 and calcium con- centrations. Troponin-T degradation and Warner- Bratzler shear force were measured as indicators of Key Words: Beef, 25-Hydroxyvitamin D 3 , Tenderness, Troponin-T 2004 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2004. 82:1410–1418 Introduction Although inconsistencies exist as to the efficacy of dietary vitamin D 3 and beef tenderness, vitamin D 3 , in general, is a nutritional means of elevating muscle calcium concentrations and improving beef tenderness (Swanek et al., 1999; Montgomery et al., 2000, 2002). Elevated muscle calcium concentration enhances the calcium-dependent myofibrilliar protein degradation postmortem to improve tenderness (Koohmaraie, 1988; Koohmaraie et al., 1991). 1 Funding granted by Iowa Beef Industry Council and by the Wise and Helen Burroughs research endowment. The authors acknowledge D. Hoy, D. Zimmerman, and the scientists in the Periparturient Diseases of Cattle Group of the National Animal Disease Center, USDA-ARS for their assistance with laboratory analyses and data in- terpretation. 2 Correspondence: 313 B Kildee Hall (phone: 515-294-5626; fax: 515-294-6445; e-mail: dcbeitz@iastate.edu). Received July 1, 2003. Accepted January 15, 2004. 1410 tenderness for loin steaks collected at slaughter and aged for 6 or 14 d postmortem. Muscle samples, col- lected concurrently, were assayed for 25-OH D 3 and calcium concentrations. A single oral bolus of 25-OH D 3 was sufficient to increase plasma 25-OH D 3 concen- trations (P < 0.001) through slaughter, regardless of dose or time of bolus administration. The single oral bolus of 25-OH D 3 , however, did not increase plasma calcium concentrations (P > 0.05). As a result, neither troponin-T degradation nor Warner-Bratzler shear force was improved (P > 0.05) by treatment. Muscle 25- OH D 3 concentrations were increased (P > 0.001) by treatment with 25-OH D 3 . Although sustained plasma 25-OH D 3 concentrations did not increase plasma or muscle calcium at slaughter nor influence tenderness, the use of 25-OH D 3 as a nutritional means of improving beef tenderness is in its infancy, and more research to delineate an effective dose and the potential interaction of seasonal exposure to ultraviolet light is warranted. Feeding excess vitamin D 3 close to slaughter results in higher concentrations of vitamin D 3 and 25-hydroxy- vitamin D 3 (25-OH D 3 ) in muscle (Montgomery et al., 2002; Foote et al., 2004). Calcification of soft tissues has resulted from excessive (80,000 IU/mo) dietary vita- min D, and concerns regarding the health risk of foods high in vitamin D content have been raised (Rajasree et al., 2002). Feeding 25-OH D 3 , however, results in muscle vitamin D 3 concentrations similar to those of control steers, and 25-OH D 3 concentrations one-third the concentration for vitamin D 3 -treated steers (Foote et al., 2004). Foote et al. (2004) reported that a single oral bolus of 25-OH D 3 increased plasma Ca for up to 20 d and resulted in LM Warner-Bratzler shear force (WBSF) and troponin-T degradation values that were intermediate to those of control and vitamin D 3 -treated steers. We hypothesize that the length of time between the administration of a single oral bolus of 25-OH D 3 and slaughter can vary and may result in elevated plasma and muscle Ca at slaughter and improved ten- derness. A variable length of time between 25-OH D 3