Stress induced meat quality problems such as dark cutters cause large monetary losses to the livestock industry. The National Beef Quality Audit estimates that dark cutters cost the beef industry $5.00 for every fed animal slaughtered. Dark cutting beef is darker and drier than normal and has a shorter shelf life. Good quality beef has a final pH value close to 5.5. At pH values of 5.8 and above, both the tenderness and keeping quality of the fresh chilled meat is adversely affected. High pH meat is unsuitable for the premium trade in vacuum-packed fresh meats, and, depending in the commercial use of the product, dark-cutting meat may be discounted by 10% or more (Tarrant,1981). High meat pH is caused by an abnormally low concentration of lactic acid. Post mortem production of lactic acid requires an adequate content of glycogen in the muscles at slaughter. Ante mortem glycogen breakdown is triggered by increased adrenaline release in stressful situations, or by strenuous muscle activity.
To reduce stress, prevent fighting and preserve meat quality, strange animals should not be mixed shortly before slaughter. A majority of the dark-cutting in cattle is due to mounting behaviour, and when strange bulls are mixed, the physical activity during fighting increases dark-cutting as well.
Good reviews on dark cutting beef can be found in Fabiansson et al.,(1988) and Hood and Tarrent(1981).
High financial losses are incurred by the livestock industry as a result of carcass bruising (Dow,1976; Hails,1978; Grandin,1980; Wythes and Shorthose,1984; Eldridge and Winfielddd,1988). Bruising is an impact injury that can occur at any stage in the transport chain and may be attributed to poor design of handling facilities, ignorant and abusive stockmanship, and poor road driving techniques during transportation (Grandin,1981). Contrary to popular belief, livestock can be bruised moments before slaughter and stunned cattle can be bruised until they are bled.