Whether calf housing is new construction or a conversion, ventilation is a major factor in maintaining healthy animals.
John Tyson, Penn State ag engineer, said young dairy calves deal with a variety of health threats – from fecal/oral disease transmission, animal-to-animal disease transmission, poor air quality, drafts and extreme cold and heat. One factor that invites pneumonia is a high humidity environment, which often occurs in calf housing due to damp bedding and high levels of ammonia resulting from poor air movement. Overcrowding and other stressors can also contribute to pneumonia.
Good air exchange and ventilation can help with disease management. One goal for barn design is good air exchange to control levels of moisture, gases and pollutants. “Remove moisture from the facility and bring fresh air in,” Tyson said. “The ventilation system should also have uniform distribution.” The overall air exchange rate must be sufficient for the building and ventilate evenly throughout the shelter, particularly at animal level.
Minimizing drafts in the building is essential. A draft is anything over 50 feet/minute (the equivalent of 0.75 mph). However, Tyson noted the original interpretation of “draft” isn’t up to date, and animals can probably handle more of a draft. “I think they can have faster air movement at animal level,” he said, “depending on other factors such as bedding and health.”
While a mature cow’s comfort level ranges from subzero to 75º, the young calf’s comfort zone is between 58º and 78º. When calves reach about one month of age and have some fat reserves, they can handle colder temperatures, but still not as much as a mature dairy animal. In cold temps, farmers should consider additional draft protection such as deep bedding.
Tyson broke down ventilation needs by the season. “We’re focused more on drafts during cold weather,” he said. “In warmer seasons, we still need adequate air exchange but we’re trying to remove excess heat and provide shade and remove hot spots within a building. The most challenging time of year [is] during fall and spring when there are wide temperature swings.” During this time, calves need protection from cold wind, precipitation, drafts and, in some cases, fans are required during the day.
Moisture control drives ventilation for young animals. It can be difficult, but it’s the most important goal. “An 80- to 100-pound newborn calf in 30º to 35º exhausts about one ounce of water per hour,” Tyson said. “That doesn’t sound like a lot of water but on top of that is water that’s being vaporized from feed, water and manure.” Most calves live on a manure pack for the first two months of life, so moisture from manure becomes a consideration. Manure moisture must be removed by the ventilation system via air exchange.
“Ambient air (outside the shelter) has a given moisture content,” said Tyson. “If it’s cold, heavy air, it has a given volume and a given moisture content or relative humidity. If we add heat to air, air expands and becomes lighter and more absorbent of water. Relative humidity is drastically reduced, and we’ve created a sponge. If we bring outside air in and mix it with air in the building, and use some heat from the animal, the ‘sponge’ can soak up water and the exhaust out.”
During winter, mature dairy animals produce sufficient heat to heat the air around themselves and create thermal buoyancy. Calves have limited ability to make such a system work, and in calf barns, Tyson said it’s unadvisable to have temperature differences greater than five degrees from inside to outside. “If there’s a greater difference than that, we run the risk of air quality issues and more moisture problems in the building that lead to respiratory issues in those animals,” he said. “We’re striving to keep temperatures much the same, which drives us to have more ventilation because we don’t have heating ability.”
Small-scale natural ventilation is why calf hutches work well even in winter. Hutches can be sited according to prevailing winds to take advantage of the natural pressure difference created by the winds.
Some calf barns can handle higher wind, but animals must be well-bedded, dry and perhaps jacketed to help conserve energy. “Allow them to have fresh air at their nose,” said Tyson, “but not suffer due to cold temperatures or air movement.”
In winter, air blows over the building, and the shape of the building creates pressure differences that will allow air to leave through a ridge vent or the leeward wall of the building with small amounts through the windward side.
One problem with longer buildings is prevailing winds coming at an angle. The leeward side of the building will have a lower pressure and will pull air back in as it blows by. In long, narrow buildings, this creates a wind swirl or draft effect, and even though the back wall is closed, air now enters through the open front.
“What we recommend for open-front buildings that are long and narrow is some type of swirl barriers placed every second to third pen,” said Tyson. “It’s a solid wall that prevents air from blowing down the backside of the building and gives calves somewhere to move away from the front of the building in windy conditions and find draft-free, fresh air at the back of the shelter.”
Tyson said that in naturally ventilated buildings, pens should be moved away from the outside wall. This creates an observation and working alley and removes animals from the cold wall and cold air at the curtain that can drop directly down. This design creates a tempering area where air is mixed before it drops onto calves.
Closed curtains in a cool barn present issues because there will be periods of little to no natural air flow. In wide buildings, it’s difficult to achieve even air distribution, so many calf barns include a positive pressure ventilation system.
Fans are used to increase the static pressure within the building, forcing air in, and stale air is pushed out through planned escape.
The design goals for a positive pressure system are to deliver fresh air evenly throughout the shelter and to push air to animal level without causing a draft.
“We can deliver air to the animal close to the floor but not directly onto the animal,” said Tyson. “We want the air to mix throughout the shelter and dilute moisture and gases, then remove those elements when air is exhausted.”
by Sally Colby