Free stall barns are designed to protect cows from hot summer sun, cold winter winds, snow and rain. Temperatures do not have to be kept above freezing. As long as cows are adequately sheltered from wind and rain, they cope quite well in temperatures below 20 degrees F.
Under normal circumstances, natural ventilation works fine in the majority of free stall barns. During particularly hot periods, fans to mix the inside air with outside air and increase air flow over the cows are required.
Cows begin to suffer from heat stress at temperatures of around 25 deg C or lower if humidity becomes higher than 90 per cent. This causes reduced DMI, or dry matter intake, reproduction ability and milk production. This does varies from breed to breed. To avoid risking this reduction of profitably, free stall barns should be built to permit end and side walls to be removed completely, in order to increase overall air flow and take advantage of cooling breezes.
During winter months, some ventilation is necessary to allow manure gases, odor and moisture to be removed. The difference between outside and inside temperatures should not be above 5 deg C, as this would cause condensation, which would accelerate deterioration of the barn and create an unhealthy environment for the cows.
Continuous ridge openings are required throughout the year. For every 3m of building width, a 5cm ridge opening should be provided. A 27m building width, for instance, would require an open ridge of 45cm.
In very cold weather, each side wall requires a continuous opening of half the ridge opening. In other words, a 27m building would need a 23cm opening on the top of each side wall.
Mild spring, fall and winter weather require continuous, adjustable end and side wall openings. Adjustable, 1m high openings above top of cow level, as well as adjustable openings on end walls – also above cow or door levels – are essential. Openings should be adjusted to minimize any drafts and keep inside temperatures at levels within 5-6 degrees C of those outside.
In summer, additional openings at the level of the animals are necessary. Side and end walls should be removed entirely during very hot spells. Essentially, the barn should only serve as an umbrella or sunshade during summer.
Used to create air flow over cows’ backs, fans can be controlled with thermostats and are frequently used in pairs, with one activating at 21 degrees C and the second activating at 26 degrees C. They provide good drafts, but do not exchange air, so they are not an alternative to natural ventilation.
Fans should blow in one direction and be installed at 3.6m height. To ensure air flows over the backs of cows, they should then be angled at around 20 degrees, facing down. 36″ fans need to be placed at a distance of 9m, 48″ fans should be at 12m intervals. Effectively, distances kept must ensure air velocity of 3.5-5.6 kph.