Submitted to: American Meat Science Association Conference Reciprocal Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2014
Publication Date: 6/1/2014
Citation: Shackelford, S.D., King, D.A., Hales, K.E., Wheeler, T.L. 2014. Effect of Ractopamine Hydrochloride and Zilpaterol Hydrochloride on tenderness of Longissimus steaks of Bos Taurus steers(abstract). American Meat Science Association Conference Reciprocal Meat Conference, Abstract No. 69. Available: http://18.104.22.168/docs/default-source/publications-resources/rmc/2014/2014-rmc-abstracts.pdf?sfvrsn=0
Technical Abstract: Objectives: Three experiments were conducted to determine 1) the interaction of ractopamine hydrochloride (RH) inclusion rate (0 or 300 mg·hd-1·d-1 for last 30 to 34 d before harvest) and dietary protein level (13.5 or 17.5% CP) on LM slice shear force (SSF) at 14 d postmortem (Exp. 1); 2) the interaction of zilpaterol hydrochloride (ZH) inclusion rate (0 (ZH0) or 84 (ZH84) mg·hd-1·d-1 for 21 d with 3 to 5 d withdrawal before harvest) and dietary WDGS level (0 vs 30%) on LM SSF at 14 d postmortem (Exp. 2); 3) the interaction of ZH, dietary WDGS level, and postmortem aging period (7, 14, 28, or 42 d) on LM SSF (Exp. 3). Materials and Methods: Calf-fed Bos taurus crossbred steers (Exp. 1, n = 448; Exp. 2, n = 438) were harvested at a large-scale Midwestern commercial beef processing plant and then carcasses were chilled conventionally and graded at approximately 37 h postmortem. Subsequently, a LM steak (2.54 cm thick) was obtained from the anterior end (i.e., 13th rib) of the strip loin of the left side of each carcass, aged (1°C) until 14 d postmortem, cooked to an internal temperature of 71°C, and sampled for SSF. For Exp. 3, a subsample of U.S. Choice carcasses (n = 100) were selected from each of the four dietary treatment combinations (n = 25 per treatment combination) of Exp. 2. The strip loin was obtained from the left side of each carcass and aged (1°C). Subsequently, a steak was obtained from each strip loin at each postmortem aging period (7, 14, 28, or 42 d) and LM SSF was determined. Results: °In Exp. 1, LM SSF increased with RH inclusion rate (P < 0.03; 15.4 vs 14.1 kg). But, LM SSF was not affected by dietary protein level or the interaction of RH with dietary protein level (P > 0.10). In Exp. 2, LM SSF increased with ZH inclusion rate (P < 0.0001; 24.2 vs 16.2 kg). But, LM SSF was not affected by WDGS level or the interaction of ZH with WDGS level (P > 0.10). In Exp. 3, ZH and postmortem aging period interacted to affect LM SSF (P < 0.0001). The LM SSF of ZH84 was higher than that of ZH0 at 7 (28.4 vs 19.8 kg; P < 0.0001), 14 (22.0 vs 15.1 kg; P < 0.0001), 28 (16.4 vs 12.3 kg; P < 0.0001), and 42 (13.9 vs 10.9 kg; P < 0.01) d postmortem. The LM SSF of ZH84 at 14 d postmortem was greater than the LM SSF of ZH0 at 7 d (P < 0.05). Inclusion rate of ZH and postmortem aging period interacted to affect the level of LM postmortem proteolysis as assessed with western blotting for desmin (Figure 1; P < 0.01). The amount of desmin degraded was lower for LM of ZH84 than that of ZH0 at each aging time but the magnitude of the effect decreased with aging. The amount of LM desmin degraded for ZH84 at 14 d postmortem was lower than the amount of LM desmin degraded for ZH0 at 7 d (P < 0.05). Extrapolation between observations made at 28 and 42 d postmortem, suggests that 34 and 33 d of postmortem storage are required for LM of ZH84 to achieve the same SSF and level of postmortem proteolysis, respectively, as LM of ZH0 at 14 d postmortem. Conclusion: These data show that ß-agonists, particularly ZH,can negatively impact beef tenderness and that significant lengthening of aging protocols would be required to overcome the negative effect of ZH on beef LM tenderness.