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.
The ventilation tubes in this barn provide a continuous, gentle supply of fresh outdoor air to calf pens. 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.