By John Tyson
The goal of a ventilation system is to control heat and moisture within a shelter and remove other gases and pollutants. In the winter the focus needs to be on controlling and removing excess moisture produced within the shelter. Cold temperatures within calf housing do not affect calf health during the winter, however damp and wet air in that calf housing during the winter has a large negative effect on calf health.
Calves are constantly producing water vapor as they breathe. At 37°F it is estimated that a calf is producing about 1.25 ounces of water per hour. While that may not seem like much, it adds up over time. During a 24-hour period that water is almost 2 pounds or 1 quart of water per calf that needs removed from the shelter.
One issue with winter ventilation lies within the properties of air itself. Cool/cold air can not hold nearly as much water vapor as warm air. If air within the shelter is not constantly replaced with fresh outside air, this moisture can begin to condense on surfaces within the shelter such as the floor, ceiling, and pen dividers. These "wet" conditions within the shelter can lead to disease outbreaks and transmission.
During winter conditions it is common in housing for lactating animals to be 5 to 10 degrees F warmer than outside conditions. While it may not seem like much, this difference of temperature between the air being exhausted and the air coming into the shelter allows for excess moisture to be absorbed along the way. This temperature difference also helps drive natural ventilation through thermal buoyancy. However, calves produce little to no excess sensible heat due to their limited body size. Therefore, there will be little to no temperature difference between inside and outside. This makes natural ventilation for calf shelters more of a challenge during the winter.
How much air exchange is needed to remove this moisture? Here in Pennsylvania, it has been found that designing a ventilation system in a calf shelter with a minimum air exchange rate of 8 to 10 whole building air changes per hour works well. While that may seem high compared to design standards from other areas of the United States, the difference comes down to climate. Here in Pennsylvania, the winter climate is much warmer than in the Upper Midwest. While there may be a few hours per year that temperatures are below zero much of the time it is not. In fact, less than one percent of the year the temperature is below 5 degrees F in Pennsylvania.
Good ventilation not only provides the needed air exchange, but also provides good air distribution throughout the shelter. This can be a struggle with the lower ventilation rates of winter, leading to areas of the shelter with air that is very stale and wet while other areas have good air quality. The need for proper air distribution makes the use of a positive pressure ventilation (PPV) system very attractive. Well designed and managed this system will deliver fresh air more evenly throughout the shelter and help eliminate areas with stagnant damp air.
What this higher exchange rate does mean is that design, maintenance, and management of the system must be correct. The ventilation needs to be properly designed to avoid drafts at animal level. Good bedding use and management is needed to allow ‘nesting’ of calves in cold temperatures and help the calf maintain a dry, erect hair coat. This along with the possible use of calf jackets will help the calf retain the body heat that they produce. Proper nutrition also needs to be provided to the calves.
The calf hutch is often used as the "Gold Standard" when evaluating other calf housing options. In the winter the calf hutch provides a draft-free area in the rear of the hutch for the animal to shelter when needed. She can move forward, closer to the front opening, to an area with a higher exchange when she wants. All of this comes with a dry resting area for comfort and nesting along with keeping the hair coat dry. This dry resting surface and dry hair coat help the calf minimize body heat loss to the cold environment. When farms consider more enclosed calf housing options other than hutches it is often to make caring of animals easier or to increase the comfort of the caregiver not the calf. So, before that first cold day of winter, take a look at your calf housing from the calf’s point of view and what she needs to stay healthy and make adjustments as needed.Source : psu.edu