Effet du transport sur le bien-être des animaux et la qualité des viandes

Résumé

Farm animals raised for livestock production may be transported on different occasions, including when they are taken to the abattoir. The duration of this transportation can influence the ultimate quality of the meat obtained due to the stress experienced. In addition, this transport-induced stress obviously has a negative impact on the welfare of the animals. This paper explores the link between the transportation of farm animals raised for meat and the ultimate quality of the meat produced. Interventions that minimize the negative effects of transport on animal welfare and meat quality are also presented. Transportation, including associated handling and management procedures, can be unusual for most domestic animals. In most animals, a novel situation is stressful and induces a stress response. This response includes psychological reactions, such as fear, as well as physiological reactions, including significant changes in endocrine, enzymatic, metabolite, electrolyte, thermoregulatory and hydration parameters. These changes in an animal's physiology can ultimately have a negative impact on both live weight loss and meat quality. A brief review of the process whereby muscle is transformed into meat following slaughter will help clarify this link with the stress response. Following slaughter, blood circulation ceases and the muscle tissue starts producing ATP anaerobically. To do so, it uses its glucose reserves in the form of glycogen, and produces lactic acid as a by-product. This causes a decline in muscle pH, and ATP production stops and rigor mortis develops when there is no more glycogen. The ultimate pH in muscle (Figure 1) depends on its glycogen reserves prior to slaughter, and these reserves closely depend on the level and duration of preslaughter stress. Long-term stress depletes glycogen reserves and results in a higher than normal ultimate pH-producing dark, firm, dry meat (DFD). This depletion of glycogen reserves can be induced by removal of food and water prior to transportation (Table 1). It can also be exacerbated by aggressive encounters with unfamiliar animals (Table 2). Glycogen will metabolise quicker when there is acute stress just prior to slaughter-resulting in pale, soft, exudative meat (PSE). Transportation also has a negative impact on meat quality in other ways. For example, muscle damage, as measured by creatine phosphokinase (CPK) activity (Figure 2) or by the incidence of bruising (Figure 3), is evident in transported animals. The transport conditions also influence the ultimate meat quality. In cattle, the combination of increasing time off feed and longer transportation distances prior to slaughter has been shown to decrease meat tenderness (Figure 4). In pigs, an increased loading density in the truck increases the ultimate pH of the meat (Table 3), while in chickens, a high ambient temperature in the truck (40° C) leads to the production of pale, soft, exudative meat (PSE). An extended transport duration has been shown to increase muscle damage in steers (Figures 5A and 5B), while decreasing meat juiciness and tenderness in veal calves (Figure 6). One of the most overlooked factors relating to the effect of transport on meat quality is the skill of the driver, i.e. a driver who is careful will minimize loss of balance and thus carcass bruising in the animals. Improvements in animal handling and transport equipment as well as management procedures can help minimize - but not eliminating - these negative effects. In addition, nutritional modulation of the animal's response to transport has been implemented for preventative or restorative purposes. Empirical evidence obtained to date suggests that such a strategy is effective in reducing the impact of transportation on animal live weight loss and meat quality in cattle (Figure 7 ; Table 4), and in pigs. It should be noted that the best strategy for reducing the negative effects of transportation on animal welfare and on the quality of the meat produced is to train and educate the personnel working with these animals so that they will be aware of the ultimate consequences of their actions.