Vitamin D enhancement of muscle tenderness in steers fed zilpaterol hydrochloride

Kathleen T Korn, Purdue University

Abstract

Tenderness is such an important quality of beef that consumers are willing to pay more for beef that is guaranteed tender. Although advancements have been made in producing a tender product, tenderness of retail cuts remains variable. Zilpaterol hydrochloride (ZH) is a feed additive that is fed for 21 d prior to slaughter to increase muscle size; unfortunately, it often results in tougher beef cuts. Vitamin D3 can improve beef tenderness when it is fed to steers in amounts greater than 1 × 106 IU for 4 to 14 d prior to slaughter. The hypothesis for this thesis was that feeding 250,000 IU for 165 d (long-term D) or 5 × 106 IU vitamin D3 for 10 days (short-term D) prior to slaughter would improve tenderness of steaks from steers fed ZH for 21 d. To test this hypothesis 210 steers were allotted to 6 treatments (35 steers per treatment): no supplemental vitamin D3 (ND) with no ZH (NDNZ), ND with ZH (NDZ), 250,000 IU vitamin D3 fed for 165 d (LD) with no ZH (LDNZ), LD with ZH (LDZ), or 5 x 106 IU vitamin D3 fed for 10 days (SD) with no ZH (SDNZ) or with ZH (SDZ). Carcass weights, dressing percent, and LM area were greater (P < 0.02) whereas, marbling scores, fat thickness, and yield grade were lower (P < 0.03) for ZH steers compared with no-ZH (NZ) steers. Steaks from ZH treated steers were tougher than steaks from NZ steers when aged for 7, 14, or 21 d (P < 0.01). Final BW and fat thickness decreased in SDNZ steers compared to NDNZ steers (P < 0.03). Vitamin D3 supplementation did not improve beef tenderness and tended to increase toughness in steaks aged 21 d post-mortem when LDZ was compared with NDZ (P = 0.06). Short-term D increased plasma total and ionic calcium (P < 0.01) and increased vitamin D metabolites in muscle, liver, and kidney. However, SD did not increase tissue total calcium (P = 0.17). Short-term D did increase tissue ionic calcium when ZH was not fed (P < 0.01). Tissue ionic calcium was higher in LDNZ steers than NDNZ steers, but was lower in LDZ steers compared to NDZ steers (P < 0.01). Steers fed ZH had decreased expression of Mhy1 and 2a muscle fibers compared with NZ steers (P < 0.05). Expression of Mhy2a increased in SDNZ steers compared to NDNZ steers (P < 0.03). Vitamin D3 treatment did not alter calpain, calpastatin, or PPAR mRNA expression. However, ZH tended to decrease calpain mRNA expression (P < 0.09). In conclusion, feeding ZH improved feedlot performance and improved yield grades, but resulted in lower marbling scores and tougher steaks, possibly because of a change in muscle fiber type and decreased calpain expression. Furthermore, vitamin D3 did not improve tenderness, which could be the result of calcium not increasing in the muscle of steers fed ZH and steaks from steers not fed ZH being too tender to detect a significant improvement.

Degree

M.S.

Advisors

Schoonmaker, Purdue University.

Subject Area

Animal sciences

COinS