Effects of Dietary Stress on Dark-Cutting Beef

The advantages of bulls compared with steers in production efficiency, performance, and carcass leanness have been well documented. However, it has also been well documented that meat obtained from bulls is darker in color and less tender than meat produced by steers. It may be concluded that the superiority in production performance of bulls over steers has not been exploited largely due to meat characteristics that differ from those of steers. Postmortem (after slaughter) muscle color is directly associated with antemortem (pre-slaughter) muscle glycogen content, postmortem muscle pH decline, and ultimate muscle pH, which, in tum, is affected by live animal physiological stress. In several mammalian species, depletion of muscle glycogen by exercise was followed by repletion to greater content of muscle glycogen than observed before exercise. In a lab study, starvation for 48 h followed by 48 h of refeeding rats a 65 percent glucose diet resulted in an increase and overshoot in the activities of muscle glucose 6-phosphate dehydrogenase, malic enzyme, and muscle glycogen content. The objective of the present study was to determine the effects of fasting on bull muscle glycogen content and repletion rates