Department of Animal Sciences, Colorado State University, Fort Collins 80523-1171, USA.
J Anim Sci. 2010 Jan;88(1):349-60. doi: 10.2527/jas.2009-2264. Epub 2009 Sep 25.
Calf-fed heifers (n = 72) and steers (n = 72) were supplemented with 4 levels (0, 0.25, 0.50, and 0.75%) of dietary Mg as MgO during the final 14 d of finishing and were commingled 1 d before slaughter (inducing stress by mixing unfamiliar cattle) to examine the effects of sex class and Mg supplementation on stress responses and LM quality characteristics. Heifers and steers exhibited markedly different stress responses. Heifers were more excitable than steers during preslaughter handling events and exhibited a short-term physiological stress response that involved acute sympatho-adrenal activation and resulted in increased meat toughness, without a concomitant increase in muscle pH. Steers, on the other hand, exhibited greater physical activity, associated with agonistic behavior, during the mixing period and therefore produced carcasses with lesser (P = 0.008) LM glycogen concentrations and greater (P = 0.042) 48-h LM pH values, compared with heifers. Steers also produced tougher (P = 0.008) LM steaks than did heifers. Within the range of pH values observed in this study (5.3 to 6.1), positive, linear relationships between 48-h LM pH and mean LM shear force (P < 0.05) were observed in both heifers (r = 0.25) and steers (r = 0.37). Effects of pH on LM shear force (P < 0.05), which were most pronounced at 3 and 7 d postmortem, diminished during postmortem aging and were no longer evident (P > 0.05) once LM samples had been aged for 21 d. Results suggested that toughness of LM steaks from beef carcasses with final LM pH values greater than 5.65 could be problematic unless LM cuts are aged for approximately 18 d or longer. Supplementation with dietary Mg increased (P = 0.011) serum Mg concentration, but had no effect (P > 0.05) on any of the physiological stress indicators or LM quality characteristics measured in this study. There was no evidence to support the premise that Mg supplementation of cattle lessens the effects of preslaughter stress on beef quality characteristics.
在育肥的最后 14 天，用 4 个水平（0、0.25、0.50 和 0.75%）的氧化镁作为日粮补充物来补充小牛（n=72）和公牛（n=72），并在屠宰前 1 天混合（通过混合不熟悉的牛来引起应激），以研究性别类别和镁补充对应激反应和 LM 质量特性的影响。小母牛和公牛表现出明显不同的应激反应。在宰前处理过程中小母牛比公牛更兴奋，表现出短期的生理应激反应，涉及到急性交感肾上腺激活，导致肌肉嫩度增加，而肌肉 pH 值没有相应增加。另一方面，公牛在混合期表现出更大的身体活动，与争斗行为有关，因此与小母牛相比，公牛产生的 LM 糖原浓度更低（P=0.008），48 小时 LM pH 值更高（P=0.042）。与小母牛相比，公牛还生产出更坚韧的（P=0.008）LM 牛排。在本研究中观察到的 pH 值范围内（5.3 至 6.1），在小母牛（r=0.25）和公牛（r=0.37）中都观察到 48 小时 LM pH 值与平均 LM 剪切力之间呈正线性关系（P<0.05）。pH 值对 LM 剪切力的影响（P<0.05）在死后 3 和 7 天最为明显，随着死后老化而减弱，一旦 LM 样本老化 21 天，就不再明显（P>0.05）。结果表明，除非 LM 切口老化约 18 天或更长时间，否则最终 LM pH 值大于 5.65 的牛肉胴体 LM 牛排的韧性可能会成为问题。日粮补充镁增加了（P=0.011）血清镁浓度，但对本研究中测量的任何生理应激指标或 LM 质量特性都没有影响（P>0.05）。没有证据支持这样的前提，即给牛补充镁可以减轻宰前应激对牛肉质量特性的影响。
