One advantage of group housing systems is that sows can better interact with and control their immediate environment, including thermal conditions. Sows housed in groups have the freedom to exhibit thermoregulatory behaviour such as huddling to maintain comfort even when the temperature in the barn is lowered. Barn temperatures currently maintained in barns with sows housed in individual stalls are based on the reported lower critical temperature (LCT) (Geuyen et al., 1984). Allowing the temperature to drop below LCT will require additional feed to maintain the sow body condition and weight gain over the gestation period. It has been estimated that sows housed in groups may have LCT values significantly lower than 15°C when given the ability to utilize thermoregulatory behaviour. Thus, if group-housed sows can maintain body condition and weight gain at temperatures lower than currently maintained in sow barns without the need for additional feed, the potential exists to significantly reduce energy costs for heating and ventilation.
Ventilation affects many aspects of the animal environment as well as barn operating costs, specifically energy costs. Retaining the existing ventilation system in a converted group-housed sow barn leads to over-ventilation during winter because the existing minimum ventilation fans are designed for higher animal density, thereby using extra heating fuel, and most likely causing chilling of the animals and affecting its performance. According to Harmon et al. (2010), if ventilation is continued at the pre-remodeling level (prior to conversion to group housing), the building would be over ventilated by about 33% higher than required.An estimate of energy use for an over-ventilated facility indicated that over ventilating by 30% can raise heating energy consumption by 75%. During summer, the impacts are less pronounced but over-ventilation will use extra electricity which translates to higher electricity cost (Harmon, 2013). In addition, the transitioning of the ventilation system design from stalls to group housing is not simply reducing the ventilation rate but requires careful reconfiguration to ensure proper air distribution throughout the room to eliminate dead spots (unventilated areas) and unwanted drafts.
Air exchange is critical to providing a healthy environment that fosters efficient pig growth by reducing humidity and noxious gases like ammonia and carbon dioxide. Since under-ventilation creates an unhealthy environment and over-ventilation wastes valuable heating and electrical energy, finding the right balance is the key to a healthy environment for both animals and workers as well as to energy savings and efficiency (Harmon et al., 2010). This balance can only be achieved by careful re-design of the existing ventilation system of a converted gestation barn.
Results from the computer simulation work have confirmed the need to re-design the ventilation system of a newly-converted group sow housing facility. Among all the design configurations tested, horizontal fl ow ventilation system was the most effective in removing heat from the animal occupied zone (AOZ) in the room during both summer and winter seasons. In-barn evaluation of the selected ventilation system design showed about 21% reduction in natural gas consumption during heating season and 14% reduction in electricity consumption in the room with the horizontal flow ventilation system relative to the control room with the unmodified ventilation system.
The new ventilation system design for group sow housing has provided better air quality and cleaner floors than the unmodified ventilation design. Also, the room with the new ventilation design had relatively cleaner floors than the room with the unmodified ventilation design. Animal performance and productivity were not adversely nor beneficially impacted by having a horizontal fl ow ventilation system in a gestation room.