Key Design Features for All Calf Barns
Whether calves will be housed individually or in groups, all calf barns should have the following key features:
- Spatial allowances of at least 35 square feet (3.3 sq m) or more of bedded space per calf, not including service alleys
- Deeply bedded surfaces in cool weather less than 50° F (10° C)
- Drainage below the bedding
- Multiple smaller barns that allow for “all-in, all-out” groupings, which allow for complete cleaning and downtime between uses
- Natural ventilation supplemented with positive pressure tube ventilation (PPTV)
- Minimal solid sidewalls limited to 2 feet (61 cm) high
Space Allowance per Calf
Provision of sufficient space per calf is the single most important determinant of air quality in a calf barn. Based upon airborne bacterial density studies1, we recommend that calf pens should provide a minimum of ~35 square feet (3.3 sq m) of bedded space per calf. We have clinical experience with farms that have tried to ventilate calf facilities successfully by allocating 15 square feet (1.4 sq m) of bedded space per calf, but have failed repeatedly.
Deep Bedding
Deeply bedded resting areas are critical for very young calves in cold weather. The thermoneutral zone of newborn calves is 50 to 78° F (10 to 26° C), but drops to 32 to 73° F (0 to 23° C) by one month of age2. A newborn calf lying on top of a bare floor at 45° F (7° C) will lose core body temperature without some thermal support. Deep bedding allows the calf to build up a layer of heat within the bed and minimize heat loss. The University of Wisconsin-Madison School of Veterinary Medicine developed a scoring system to evaluate the sufficiency of bedding called “Nesting Score”1. It is a simple visual evaluation of the visibility of the rear leg of a calf lying down in the bedding. If the entire leg is visible, it is scored as Nesting Score 1. If partially obscured by loose bedding, it is Nesting Score 2. If the rear leg is completely obscured by bedding, it is Nesting Score 3. Provision of deep bedding, such as straw, or moderate bedding plus calf jackets, are important factors in preventing respiratory disease in cold weather.
It is our opinion that calf jackets are equivalent to approximately one unit of Nesting Score. In other words, provision of Nesting Score 2 plus a calf jacket is approximately equal to Nesting Score 3 without calf jackets. While Nesting Score 1 is satisfactory during warm weather, the addition of calf jackets to a Nesting Score 1 surface does not appear to achieve the desired level of thermal support in cold weather.
Drainage Below the Bedding
To maintain a deeply bedded surface, it is critical for the pen to have good drainage so that urine, spilled milk, and water can move out of the pen rather than soak the bedding. Excellent drainage has been achieved using a tiled gravel bed approximately 18 inches (46 cm) deep below the bedded area. The area should be fitted with drainage tiles leading to a collection area outside of the calf barn. With this base, operators typically report that straw usage is half that used to maintain similar beds over a concrete surface. The tile is covered with pea gravel, and bedding is applied on top of the gravel. If relatively clean, long straw is used, the gravel will stay permeable for two to three years. Usually a small amount is removed with each cleaning of straw and is replenished each time. If the straw has a lot of fines, the gravel may need to be replaced annually. Using sand instead of gravel over the tile should be avoided as the straw bedding becomes churned into the sand as calves walk on the surface. Sawdust and wood shavings should not be used as a base layer for bedding since they will retain moisture.
To avoid skid loaders getting stuck, a larger rock gravel can be laid down. Otherwise, a gently sloped concrete floor with a slope of at least 2% that leads to one or more drainage channels of 1 to 3 feet (31 to 91 cm) in width allows skid loaders to ride over the strips of concrete.
1. Straw bedding is removed
2. Leftover straw is raked up and discarded
3. New gravel is added to the base
4. Calf pens are set up over the cleaned and rested gravel
Recently, some producers are experimenting with deep straw bedding placed over traditional slatted flooring, allowing urine and water to drain quickly from the bed. While we have little experience with the technique, it would appear to accomplish a similar end.
If the surface below the bedding must be solid concrete, three issues must be addressed through floor slopes. First, the floor needs to be sloped to move liquids out of the pen as efficiently as possible with a minimum of a 2% slope, equivalent to 2.4 inches (6 cm) per 10 feet (3.1 m). Second, liquids moved from the pen should not move into an area exposed to the foot traffic of the calf caregiver. Third, the slope needs to prevent water used in service alleys from draining into the pen and bedding. This can be accomplished with a crowned central work alley and a gutter at the immediate front of the calf pen. The pen itself can be sloped toward the front of the pen, or preferably, it could be sloped to the rear of the pen with a second drainage gutter at the rear. Drainage gutters would be designed to carry liquids to collection points outside of the building.
Multiple Smaller Barns
We have developed a strong preference for multiple, smaller barns compared to large capacity single buildings. The optimal system appears to be four or more individual nursing calf barns that allow for “all-in, all-out” management systems. With separate barns, each barn is filled with newborn calves until the barn is full, typically over a 2½ week period. At an average age of 8 weeks, the entire group of calves in the barn is weaned and moved to another space. Then the entire barn is dismantled, cleaned, and allowed to dry for a minimum of one week, preferably two weeks, before being re-assembled and used again for the next group of calves.
There are at least two significant benefits associated with this practice. First, young and vulnerable calves are not directly exposed to older calves that may be shedding infectious pathogens. Second, the ability to clean and let a barn dry out for one to two weeks between uses appears to be a powerful tool in breaking infectious disease cycles.
The barns should be spaced far enough apart to not impede natural ventilation. More information about barn spacing can be found here.
Natural Ventilation with Supplemental Positive Pressure Tube Ventilation
Natural ventilation is the preferred method of ventilation for youngstock facilities. Mechanically ventilated facilities are not recommended for calves in climates similar to Wisconsin’s since it is extremely difficult to produce a reliably-sized inlet at winter ventilation rates. Inlets typically become very small to match the required exhaust fan rate, and these small inlets deliver so little air that it is almost impossible to find consistently good air quality throughout the barn. Summer ventilation rates in negative pressure facilities are feasible with calves, but the concern with these systems is whether or not the systems are regulated well enough to avoid chilling calves during cool nights.
The other issue with negative pressure systems is where to locate the inlets and the exhaust fans. Placing the inlets on the nursing calf side of the barn subjects the youngest calves to the freshest, but coldest air. Exhausting the air out of the nursing calf side of the barn exposes the youngest calves to the oldest calves’ pathogens and contaminants. In addition, at least three levels of ventilation rates, with the ability for finer control of the system at varying heat and humidity levels, will need to be accounted for.
Natural ventilation is advantageous because natural forces are used to ventilate buildings, reducing costs for both fans and electrical power. Natural forces include wind moving through, against and over buildings, and thermal buoyancy of warmed air rising inside a building. However, natural ventilation has a number of shortcomings, especially in calf housing when winds are still. Wind roses that summarize wind conditions throughout the year are available for most parts of the United States, and can be accessed through the USDA at the following website: http://www.wcc.nrcs.usda.gov/ftpref/downloads/climate/windrose/.
When the wind is still, naturally ventilated barns are dependent upon thermal buoyancy for ventilation. Unlike adult cows, calves do not generate sufficient heat to effectively warm the air that surrounds them to allow for thermal buoyancy to occur, thus natural ventilation becomes insufficient.
Further limitations of natural ventilation occur when outside air is warmer than the air inside of the barn – a situation that occurs for a period of several hours almost every day as the sun warms the air outside the barn more quickly than inside. During these periods of time, air entering the cooler interior of the barn through eaves will rise and leave the barn without good mixing near the floor.
Because of these occasional limitations with natural ventilation, we have advocated the use of positive pressure tube ventilation systems to supplement naturally ventilated calf barns. More information about supplemental positive pressure tube ventilation systems can be found here.
Sidewall Heights
To optimize natural ventilation during warm weather, sidewalls should be sufficiently open to allow winds to easily enter the barn. Minimal sidewall height is related to barn width. In general, 12 feet (3.7 m) should be viewed as the minimal sidewall height for buildings less than 40 feet (12.2 m) in width, but in buildings of 60 feet (18.3 m) or greater in width, the sidewall height should be at least 14 feet (4.3 m). The sidewall should be fitted with retractable curtains, preferably split so that all air does not have to enter above the top of the curtain.
A minimal solid sidewall of approximately 2 feet (61 cm) above the floor is preferred for naturally ventilated calf barns. During warm weather when the sidewall curtains are fully open, the low sidewall allows wind to move directly into the calf pens and maximize ventilation. A traditional solid sidewall of 3 to 4 feet (1 to 1.22 m) high may prevent winds from reaching the calf pens, particularly if the air temperature of the wind is higher than the interior temperature of the barn. It is especially problematic when warm exterior winds pass over the high solid wall, fail to drop into the calf pen, and travel across the barn, carrying away any fresh air emerging from a positive pressure tube ventilation system. In this situation, the traditional high solid sidewall interferes with both natural and positive pressure tube ventilation.
If an existing barn has a traditional high solid sidewall, calf pen ventilation can be improved by mounting a “baffle board” on the sidewalls to deflect winds downward into the pens. The baffle board can be as simple as a wide plank of 8 to 10 inches (20 to 25 cm) wide, hinged to support posts, positioned just above the concrete sidewalls, and held on a downward angle using cables from the board to the rafters.
An example of a baffle board on a 4-foot (1.2 m) concrete sidewall to deflect wind downward into the calf pens
Translucent Panels
Translucent panels in the roof or on the end walls can allow the barn to accumulate heat more quickly as the southerly sun ascends during winter months, but they must be mounted on relatively vertical southerly walls so that they do not become a source of excess heat during the summer. To minimize added heat during summer months, mono-sloped buildings with vertical south walls are preferred. Tinted or smoked translucent panels can be placed in the upper portion of the south wall as shown in the adjacent photo, which allows for some solar heat gains in winter.
