In the United Kingdom pigs can spend up to 11 hours in transit to slaughter but on average travel for two to three hours. In the past, international journeys have lasted up to 40 hours and have been over 900 miles long. There is evidence that pigs, like calves and sheep, but unlike adult cattle, prefer to lie down if provided with suitable conditions, particularly bedding, on the vehicle. They will, however, sometimes stand during short journeys, possibly when excessive vibration or uncomfortable flooring, particularly a lack of sufficient bedding, cause discomfort. Current UK legislation and EU Directive 95/29/EC specify that, in general, pigs must have sufficient space to lie down during transit. Measurements of the space needed for sternal recumbency, and direct observations of pigs at different stocking densities, suggest that the minimum space required is equivalent to about 250 kg/m2 for normal slaughter pigs of 90 to 100 kg liveweight. This figure may not be appropriate for very small or very large pigs. In the UK at present, more than half of all slaughter pigs are transported at densities greater than that prescribed (235 kg/m2) in the EU Directive. At stocking densities above about 250 kg/m2 there may not be enough room available for all the pigs to lie down, leading to continual disturbance of recumbent animals by those seeking a place to rest. A stocking density of 322 kg/m2 leads to clear evidence of physical stress. During long journeys (≥25 hours) meat quality is reduced by high stocking densities, implying muscle glycogen depletion and possibly fatigue. Higher stocking densities are also associated with higher mortality. There is evidence of wide variations in air temperature inside transporters, particularly for international journeys. Although there are small variations within vehicles, the temperature of the air inside is closely related to the outside temperature. It has been recommended that the temperature within the vehicle should not exceed 30°C in order to remain within the pig's thermoneutral zone. Such temperatures, together with acceptably low concentrations of potentially noxious gases, such as carbon dioxide, can be achieved in moving vehicles by adequate ventilation, provided there is adequate space above the animals' heads. In tripledecked lorries, the height between decks has tended to be reduced and can be as little as 90 cm. Further work is needed to decide whether this is sufficient for modern slaughter pigs.
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