In barns with natural ventilation, the combination of the open ridge and eaves is the source of ventilation during the most severe winter weather, ie, during periods when temperatures reach the lowest levels or times when conditions are especially windy or stormy. During all other times in winter, however, additional ventilation must be provided. Typically, doorways are left open, portions of the end wall sections of the gable roof may be left uncovered, or sidewalls away from prevailing winter winds may be left open for this purpose. Then, as temperatures rise into spring and summer, sidewalls and end walls are fully opened. As a general rule, too much ventilation is preferred over too little.
Hot, muggy summer weather is one of the most critical times for animal health, comfort, and productivity. For barns with natural ventilation, completely open sidewalls and end walls allow wind to blow through the animal zone for heat stress reduction. However, when winds are calm, providing adequate air movement to avoid heat stress is difficult. Supplemental cooling can be provided in several ways. Fans are commonly used to increase air movement. The increased air velocity over the skin increases the rate at which animals are able to dissipate excess body heat. Two other methods rely on evaporative cooling to either cool the air around the animals or wet the animal’s skin and allow body heat to evaporate the water. However, water should be added to the animals’ environment only if ample air movement is present.
Barns with mechanical ventilation require staged fans to provide ventilation ranging from the minimal continuous rate, through an intermediate rate for spring and fall, to a high rate for summer. An air exchange rate of 60 air changes/hr is considered the absolute minimum for summer. Often, ventilation rates of 90–120 air changes/hr are provided for hot weather.