Consider the arrangements needed for controlling the climate not only in your pig-houses, but also on the vehicles used to transport the pigs. An advisory document issued to producers in the UK reminds them that ventilation within the vehicle is important to remove the heat and moisture produced by animals during transport. It also advocates active ventilation using mechanical fans as allowing more opportunities to modify conditions around the animals than with passive ventilation especially when the truck is stationary.
Written for the governmental department for rural affairs by ADAS Roslin Welfare Consultants, the document says the preferred method of ventilating livestock vehicles is by a process of controlled mechanical ventilation. Unlike controlled-environment systems such as those found on refrigerated trucks, this provides only a regulated ventilation rate. The temperature of the air entering through the inlet is no different from that externally. As this air passes over the pigs, it collects the heat and moisture that they have produced.
There is little opportunity to control the movement of air within a naturally ventilated vehicle, the British advisers continue. The forward motion of the transporter creates an area of low pressure around the container sides at the front end. This would have the effect of drawing in air through the rear vents when the truck moves forward at speed. The air would then move forward over the pigs and leave through the front vents.
"This effect explains why fresh shavings that have been spread evenly over the floor at the start tend to be blown to the front of an empty vehicle while it drives to the farm for loading," they comment. "Ventilation holes in the front headboard will let air into the container, but this air will be drawn out again by suction through the front vents and will not travel the length of the container." An exception occurs on a truck moving at low speed in a strong cross-wind, in which case the resulting air-flow would be through and across the container.
The document offers a diagram illustrating how a series of suitably positioned mechanical fans at the front of the truck could achieve controlled ventilation, provided that the fans were of a sufficient capacity. But, it warns, simply mounting fans on existing ventilation openings is unlikely to ensure that air flows over all the pigs, because air will always take the path of least resistance.
"It is better to install fans at one end of the vehicle containers and apertures at the other end, with closed sides in between. The direction of air-flow created by the fans should enhance the natural flow of air within the container caused by the vehicle's forward movement. Extraction fans at the front and natural inlet apertures at the rear are probably the most effective arrangement.
"However, in case of mechanical failure, a fan-ventilated vehicle should always have the capability of opening sufficient side apertures to enable emergency natural ventilation."