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Carcass contamination is more frequent when animals arrive at the plant with intestinal content. Increased stress during the pre-slaughter period in non-fasting pigs can lead to the death of animals and produce a higher frequency of pale, soft and exudative meat (PSE).
Fasting pigs before slaughter reduces mortality during transport to the abattoir. It is known that pigs that have been fed prior to loading suffer from transport sickness while being transported and vomiting more easily than pigs that have been fasted. This situation leads to a higher mortality, especially in summer and in animals genetically susceptible to stress (Guàrdia et al., 1996).
Pig processing plants seek to prevent perforation of the stomach during evisceration in order to minimize potential contamination of the carcasses with foodborne pathogens as Escherichia coli, Campylobacter, and different Salmonella species present in the stomach contents. Fasting before slaughter reduces the stomach and intestinal contents which facilitates the evisceration process reducing the possibility of perforations.
Another benefit of ante-mortem fasting in pigs is the reduction in the incidence of PSE meat. This defect occurs when the muscle energy consumption (glycolysis) after slaughter is greater and faster than normal. Fasting pigs causes a PSE meat reduction because the low energy level at slaughter which reduces the rate of muscle pH drop, producing a higher meat quality compared to non-fasted animals. PSE meat reaches a pH below 5.8 at 3 hours of slaughter, reaching less than 5.55 at 24 hours. The problem of PSE meat is greater in summer and in animals genetically sensitive to stress. PSE meat has more exudate and a very pale colour which is rejected by consumers. PSE meat causes technological problems during pork processing. For example, during ham cooking, both the technological yield and the slicing yield are increased as increasing fasting periods due to its better quality, as shown in Figure 1.
One negative aspect of fasting before slaughter is the loss of carcass weight, especially in prolonged fasting periods (more than 30 hours) accompanied by poor animal management. The rate of weight loss of the carcass practically threefold after 24 hours of fasting, decreasing significantly carcass yield (Figure 2). The results are very variable, from 60 to 140 grams per hour, which indicates that weight loss also depends on other factors such as weight at slaughter, genetics, and management (Chevillon et al., 2006). However, these losses would have to be discounted by saving more than a kilo of feed per pig for the farmer when the animals are fasted on farms. The generalized recommendation is an effective fasting period from 12 to 14 hours before loading, altogether with the time of loading, unloading and transport, and the time of waiting in the lairage gives a total fast of 22 to 26 hours.
The control of pre-slaughter fasting begins by evaluating the degree of dirt of the trucks after unloading and the dirt in the lairage pens. In the line, you can visually examine the viscera and determine if they have digestive content. The stomach weight must not exceed 1 kg. In animals raised with liquid feed this limit is higher since their stomachs weigh less. Also, non-fasted animals often have more skin damage because of the higher frequency of fights. These damages are evaluated visually in the carcasses.
Good management is necessary before the slaughter, starting from a good design of corridors and ramps, respecting the densities both in transport and in lairage, showering the animals and having access to drinking water. The implementation of farm collection pens to keep the selected pigs for slaughter allows the animals to rest and, prevents fasting those pigs not selected because they do not reach the optimum weight (Faucitano et al., 2010). It is evident that the personnel involved in these tasks must be well trained to obtain a good final quality of the pork products.
The control of ante-mortem fasting accompanied by good management guidelines is fundamental from the point of view of food safety, animal welfare and product quality.