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, clinical professor in the School of Veterinary Medicine at the University of Wisconsin-Madison, 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.
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.
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 individualpens.
Breath of fresh air
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 positivepressure 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. Generally, the diameter of the tube should be 1.3 to 1.5 times the diameter of the fan. 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.
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.
For more of his recommendations, go to: http://tinyurl.com/m59bmc3
Over the past five years, Nordlund has been involved in training more than 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 incidence of bovine respiratory disease (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.
Meanwhile, Select Sires, Inc. worked with Nordlund in designing calf barns for the high-value seedstock bull calves that the company raises. 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.
The barn features 30-inch high sidewalls, with a roll-up curtain on either side for natural ventilation.
According to Don Monke, vice president of production operations for Select Sires, the tube-ventilation worked 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 measure wind 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 ambient 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 highvalue 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 wiremesh 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.
John Maday is editor of Bovine Veterinarian, a sister publication of Dairy Herd Management.