As dairies increasingly turn to housing young calves indoors, ventilation, as it relates to animal health, becomes a key consideration. Outdoor calf hutches, of course, have served well and provide ample ventilation. Their exposure to weather, however, can result in stress on calves and extra labor for dairy workers. Also, calf hutches do not facilitate use of automated feeders.
Growing numbers of dairies are turning to calf barns with individual stalls as a lower-labor solution for providing a comfortable environment for calves. These barns typically are designed with natural ventilation that can be regulated somewhat, depending on weather conditions.
Ken Nordlund, DVM, at the University of Wisconsin (UW), has found though that even in well-ventilated barns, the individual stalls can become badly polluted microenvironments, harboring airborne pathogens. Research shows airborne bacterial counts in naturally ventilated barns can be significantly higher than those outdoors, and counts within individual calf pens can reach levels dramatically higher than in the rest of the barn. Most of the bacteria species isolated in these tests are non-pathogenic, but Nordlund says research results indicate lower total airborne bacterial counts are associated with reduced prevalence of respiratory disease in the barns. High total bacterial counts serve as an indicator of poor ventilation, and because calves spend 100 percent of their time in the pens, their exposure to the air within the microenvironment is continuous and chronic. Fields studies, he adds, have shown a relationship between airborne bacteria counts and bovine respiratory disease (BRD) in naturally ventilated barns.
Dairies frequently overlook or underestimate the incidence of BRD in calves, Nordlund says. They use appetite as an indicator, but in limitfeeding systems the calves are hungry and take their feed readily. Research from fellow UW veterinarian Sheila McGuirk, DVM, MS, PhD, ACVIM, using a clinical scoring system and ultrasound diagnostics, has shown higher rates of BRD in dairy calves than most would suspect.
So if bacterial counts reach high levels even in barns with ample natural ventilation, what can be done to reduce them? The answer lies in improving ventilation to the individual pens.
Nordlund has worked with numerous dairies, assisting in the design and use of ventilation tubes. The positive-pressure ventilation tubes are designed to drive fresh air into individual pens, he explains. These are a new generation of ventilation tubes, not the positive-pressure recirculating tube systems of the 1980s.
The goal is to continuously deliver a small amount of fresh air to the calf without creating a chilling draft. The tube system supplements natural ventilation with a non-stop supply of fresh, outside — not recirculated — air at a uniform volume along the entire length of the tube. Nordlund says these tube systems are relatively inexpensive and easy to set up but must be designed and installed correctly to achieve those goals.
The fan is mounted to the wall, so there is no recirculation. The diameter of the tube should be 1.15 to 1.3 times the diameter of the fan. Using a tube diameter larger than the fan reduces interior air speed or velocity pressure near the fan, while increasing static pressure. The design provides uniform pressure and volume of air released from all the holes along the length of the tube. If the fan is larger than the tube diameter, there will be almost no air coming out of holes along the first third of the tube, and the final third will release 20 times the volume of air at a high velocity. The system should be sized to provide approximately four interior changes in air volume per hour.
The “throw distance” to still air, defined as air moving at a speed of less than 60 feet per minute, also is important. The velocity of air exiting the holes should be just high enough to deliver a uniform flow of fresh air to each calf pen without creating a chilling draft. Air holes in the tubes should be sized so that air exits at a speed of approximately 1,200 feet per minute. If air exits two holes of different diameters at precisely the same speed, the air emerging from the larger diameter hole will have the greater throw distance. Nordlund suggests that the systems should be designed so that still air speeds are reached at a point about 4 feet above the floor, leaving the calves in fresh air without a draft. Assuming an exit velocity of 1,200 feet per minute, the throw distance to still air from 2-inch holes would be approximately 14 feet, but 11 feet from 1.5-inch holes, and 7 feet from 1-inch holes.
Nordlund has worked with several large dairies that have installed narrow, naturally ventilated barns, 35 feet wide or less, with a single tube ventilating a single row of calf pens. They use multiple all-in, all-out barns, which allow uniform age groups in each barn and thorough cleaning between uses. For wider barns, he recommends one tube for each 25 to 30 feet of width.
Over the past five years, Nordlund has been involved in training over 200 people in five countries to design and install these systems, and he says more than 2,000 barns have been fitted with the tubes. In some cases, dairies retrofitted these systems into tie-stall barns re-purposed as calf barns and into open-front heifer barns, seeing improvements in health even though ventilation seemed adequate prior to installing the tubes.
Nordlund’s studies have shown three factors associated with reduced BRD in calf barns: low airborne bacterial counts, solid panels between pens and deep bedding for insulation. Supplementing natural ventilation with positive-pressure tubes has resulted in 50 to 70 percent reductions in BRD in calf barns in many cases, achieving health similar to outdoor hutches.
One operation that made the transition is Double S Dairy, Markesan, Wis. Herd manager Dan Smits recalls the dairy built new, naturally ventilated calf barns several years ago. In these narrow barns, open to the south, each has a single row of individual calf pens. After a year of use, the dairy’s management team decided the barns did not consistently provide optimum ventilation and worked with Nordlund to install tube systems.
Smits says the dairy did not have severe problems with BRD, prior to the change, but saw noticeable improvement after installing the tubes.
Don Monke, DVM, is vice president of production operations for Select Sires, Inc., Plain City, Ohio. A few years back, he worked with Nordlund in designing calf barns for the high-value seedstock bull calves the company raises. Previously, he says, the company acquired bulls at around 6 months of age but then began bringing bull calves into their facilities as young as 30 days, to allow earlier control over their nutritional management.
This required construction of new calf barns, and Monke wanted to do everything possible to assure the comfort and health of the valuable calves. So he contacted Nordlund, who provided recommendations on barn design, positioning, ventilation and management.
The company built two calf barns at its Ohio facility, one for calves from 30 to 75 days of age and one for calves from 75 to 180 days. Both of the barns use tube-ventilation systems but are set up differently based on the requirements of the age groups.
The barn for young calves is 36 feet wide and 140 feet long, with one ventilation tube down the center. Individual calf pens are 5 feet by 7 feet and are positioned in two rows, each 5 feet from the side wall on either side of the barn to avoid down drafts from the eaves.
The ventilation tube is located within the barn’s roof trusses, 12 feet above the floor, to minimize damage from crosswinds. The barn features 30-inch high sidewalls, with a roll-up curtain on either side for natural ventilation. Based on recommendations from Nordlund, Monke used “wind-rose” data in determining the orientation of the new barns. A wind rose is a graphic tool used by meteorologists to illustrate how wind speed and direction are typically distributed at a particular location. The wind-rose patterns showed prevailing winds typically from the south, southwest or north during the warm months, so the team built the barns on an east-west orientation to capitalize on natural ventilation. Previously, at the same facility and on many commercial operations, barns were positioned more for convenience, such as perpendicular or parallel to a road, rather than for optimal ventilation.
The tube-ventilation systems, Monke says, work just as intended. If you kneel in a calf pen, you can feel the light movement of outside air from the tube at calf level. Monke purchased an anemometer to measurewind speeds at various locations and heights along the tube and confirmed the output of air is uniform and at the optimum velocity to ventilate the pens without uncomfortable drafts.
Bedding is also critical. Monke says the team uses a 6-inch base of wood shavings in each pen, with straw bedding on top as needed, depending on abient temperature, and uses the nesting-score system based on Nordlund’s recommendations.
Calf health has been excellent, Monke says, based on average daily gains and long-term performance of the high-value bull calves housed in the facility. The design, he says, has benefited Select Sires considerably.
Another factor influencing ventilation within individual pens is whether the pens are separated by solid or wire-mesh panels, and there appears to be tradeoffs involved. Nordlund says solid panels are associated with higher levels of airborne bacteria, but mesh panels have been associated with higher incidence of BRD in some trials. Nordlund recommends that if pens are separated by a solid panel, the ends and top of the pens should be as open as possible.
At the Select Sires facility, each calf pen is open on the front and back to allow circulation through the pen, with solid panels on the sides to minimize exposure between calves. At Double S Dairy, Smits says the pens had solid side panels, with a 3-foot wall on the back and open front. The team recently replaced every other side panel with wire mesh, opening each pen to one neighboring pen. Smits says this significantly improves ventilation. within the pens.
Sidebar: A cozy nest
Some producers in northern climates express concern over the cold, since the tubes operate continuously and can bring in very cold air during the winter. University of Wisconsin veterinarian Ken Nordlund and his team conducted a test at a dairy with two identical barns, one with a tube and one without. Over two weeks of monitoring temperatures during the winter, they found no difference in the average temperature. There was some minor variation, typically less than 4 percent, with the tube barn slightly colder some nights and slightly warmer some days compared with the barn using natural ventilation alone.
In any case, calf barns are subject to cold temperatures, and bedding, coupled with good drainage, are critical for calf comfort and health. Nordlund recommends using a “nesting score,” which research has shown is associated with the prevalence of BRD. He describes the nesting scores as follows:
Score 1 — The calf appears to lie on top of the bedding with legs exposed.
Score 2 — Calves nestle slightly into the bedding, but part of the legs are visible above the bedding.
Score 3 — The calf nestles deeply into the bedding material and legs are not visible.
In cold weather, Nordlund says, provide enough bedding for a nesting score of 3, or a nesting score of at least 2 with the use of calf jackets.