Tunnel Basics – Applied to Younger vs Older Birds
Whatever the age, any bird that is panting is too warm. Panting is the natural mechanism birds use to rid themselves of excess deep body heat. When a bird gets too warm, it will also cut way back on its eating – because burning more calories makes the problem worse by adding more body heat – and consequently weight gain will suffer. There are lots of other problems that pop up when birds are hot and stay hot. The worst case of course is that extreme heat increases mortalities.
Seeing lots of panting birds is the symptom that tells you the birds are out of their comfort zone and if pos- sible something needs to be done to correct the situation. There are two basic tools that are designed into a tunnel house with cool cells:
Putting an airstream directly over the birds to pick up and remove body heat (wind chill); and
Lowering the actual temperature of house air.
The house air temperature can often be lowered by just bringing in cooler air from outside. If this is not suf- ficient or possible (extreme hot weather, outside air temperature higher than inside target temperature) the cool cells are there to lower the incoming air temperature by evaporative cooling. It is really pretty basic.
A good tunnel ventilation management strategy generally is to use air movement and wind chill first, staging on various combinations of fans and air inlets, and turning on cool cells last. Actually the principles of tunnel ventilation for big birds and small birds are the same: Use the tunnel tools to balance the bird heat loss so as to keep the birds in their comfort zone. With big birds the mass to surface area ratio and R value of the bird’s surface are dramatically different from small birds that lack feathers or are not yet fully feathered. This is what makes managing tunnel ventilation on smaller birds a more demanding and less forgiving task.
Figure 1 is based on research showing how important wind chill is in keeping birds comfortable and gaining weight. At an air temperature of 85°F, five-pound birds will be suffering from excess body heat in still air and will have to be panting to shed that excess heat (left side of chart). As wind speed increases (toward right side of chart), they are able to shed enough of their body heat through wind chill so that they can resume normal breathing (and eating). For birds at three weeks and older, research shows that the wind chill effect typically does not begin to result in improved weight gain or feed efficiency until wind speed gets over 200 feet per minute.
The response of younger birds to tunnel air is very different. Figure 2 illustrates research showing just how differently younger birds experience wind chill cooling. At an air temperature of 90°F, the effective tempera- ture felt by four-week birds as tunnel wind speed increases will be 3 to 8 degrees lower than the effective temperature experienced by mature birds. The effect is even more pronounced for 1-day to 3-week birds because of their smaller body size and lack of feathers.
The most important principle to keep in mind in ventilating younger birds is that just about anything you do to increase air movement or reduce air temperature will have greater effect on young birds than on older birds. One-week birds in 98°F air will benefit from some wind chill cooling, but they don’t need nearly as much air movement or wind chill as larger birds, and if you overdo it you will chill them, which is as bad as or worse than overheating.
Tunnel Ventilation Strategies for Younger Birds
In managing tunnel ventilated houses (with perimeter vent doors) we always set ventilation programs to start out in the power ventilation vent door mode. As house temperature increases, more fans are turned on in an effort to cool the house off by bringing in outside air. In the vent door mode there is no wind chill cooling placed on the birds and no tunnel effect. If we can get the house near the desired target temperature, the birds will be comfortable. This works well if it is cooler outside than we want it to be inside. But in hot weath- er, turning on more and more fans does not lower the in-house temperature much and somewhere around 5 to 7 degrees F above target most ventilation controller programs will change the house to the tunnel mode of ventilation. This now puts a direct air stream across the birds and greatly accelerates the heat loss from the birds. If this direct airflow does not sufficiently reduce the deep body bird heat, the last step is to bring on the evaporative cooling (cool cells) and reduce the air temperature.
Most of the time with larger birds after two weeks of age, the controller can handle this with very little grower intervention. Very young birds (day old to two weeks) require a slightly different strategy and closer manage- ment.