Preslaughter and Slaughter Components

This section in general considers the meat quality changes from the live animal through slaughter, but only considers briefly factors such as breed (ie, genetics), growth, and sex. Apart from stress factors that may be breed or sex related (such as in the case of bulls where pH effects occur—see later) and animal age (which has an obvious influence only at extremes—discussed earlier) and fat cover, which affects chilling rates, the influence of these is minor. This is not to suggest that the preceding factors do not affect meat quality, but rather the effects are minor in comparison with processing effects and are perhaps overemphasized. Cold-shortening capacity appears to be greater in older animals, where the tension generated and shortenings are greater by a factor of three (80). There was shown to be a reduced tenderness in old bulls compared with young ox (81). The muscle used was beef m. sternomandibularis, which has a higher connective tissue content than other muscles. We may merely be considering the expected age-related changes in the connective tissue net in a relatively atypical muscle (see age-related toughness changes covered earlier

[62]). Similar studies have not been made on other muscles. Much work in other studies has merely revealed either no statistical difference or a minor difference between breeds and tends to focus on differences between Bos taurus and B. indicus (82). For pigs, genetic effects on meat quality exemplified by different breeds seem to be more important than for ruminants (83). In general, breed effects would pale into insignificance compared with the processing-related effects on meat quality.

Animal welfare issues for all meat species are not only consumer issues but also need to be addressed for optimum product quality and production efficiency. The effect on meat quality is subtle and is of particular important for pigs, fish, and poultry (84). Preslaughter effects commence on the farm and may arise from simple factors such as insufficient feed. From this point, mustering or rounding up, transport, and moving through races to the slaughter area contribute to bruising and stress, much of which is unnecessary. Different problems arise for pig raising facilities or feedlots for cattle than for range-fed animals. Careful design of pens, races, trucks, ramps, and other animal handling facilities can reduce many of the problems (85), but further research is needed. Washing may reduce stress in the case of pigs or can be stressful in the case of swim washing for sheep.

Slaughter procedures depend on the type of animal involved (84,86). For sheep and cattle, two types of electrical stunning can be used: head-only stunning, which allows the heart to continue beating; and head-back stunning, which causes cardiac arrest. Bleeding out and meat quality are the same with either stunning technique for lambs (87) or with delayed bleeding for beef (88). As head-only electrically stunned animals will recover within a few minutes if they are not slaughtered, the animals actually die through loss of blood initiated by the slaughterman. This type of preslaughter stunning is therefore acceptable for halal slaughter of sheep or cattle. Cattle are generally captive-bolt stunned, although percussion stunning and either type of electrical stunning can be used with no deleterious effects on bleeding out. Carbon dioxide stunning and electrical stunning are used for pigs. Carbon dioxide stunning appears to be associated with a reduced incidence of both blood splash (hemorrhages in muscle) and pale, soft, exudative meat (89), but it also seems likely that this relationship is partially a result of animal selection. Recent studies indicate that there are no welfare or issues of humaneness with current slaughter if properly applied (84,90).

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