June 8, 2018

In the Midwest Poultry Show, March 2017 edition of Poultry Talk, I discussed the importance of preparing for warm weather ventilation. With a sigh of relief, we have come through what seemed like a long and cold winter and jumped right into summer weather. However, one must always be prepared for mother nature, as the mercury can drop to cool temperatures and provide us with 30°+ temperature swings in a 24-hour period. This article will discuss some basics of warm weather ventilation concepts, one being wind chill or more specifically air speed over birds.

I recently had a phone conversation with Brian Fairchild, Professor of Poultry Science at UGA, regarding wind chill and what we really know about it for poultry. Brian noted that there really hasn’t been much work done on wind chill effect. In 2008, I attended the warm weather ventilation seminar led by Michael Czarick, also of UGA. The one thing that has stuck with me since that seminar is the potential effect of wind chill on birds. In that seminar, it was presented that the only work that has been done for poultry and wind chill was at 85°F. The chart is from that seminar showing the potential effect of increasing wind speed on birds at 85°F. I use this chart a lot to emphasize the fact that we must be mindful of what we are doing to birds and what they feel when we run air (or not) over birds during hot and cold weather. From the chart, at 600 feet per minute (fpm) air speed, the approximate wind chill or real feel to that bird is -15°F at 85°F for a real feel of 70 °F.

We all know that for an 8-20 weekold turkey, this is right in line with keeping this bird comfortable. At 85°F, a turkey will be panting and using energy to remain cool. It is outside it’s thermal neutral or comfort zone (see the table above from NC State temperature effects for turkeys). At 70°F, that same turkey is comfortable, up eating and drinking and converting calories to pounds of meat. In this case, moving 600 fpm air over birds is a huge benefit. But, what happens to a younger bird, or what happens when the actual temperature is below 85°F?

I have not been able to find a scientific answer to this question. So, we must rely on experience and Animal Husbandry 101. When I walk into a turkey house, and birds are sitting tight to the floor, I get concerned that we may be moving too much air over birds. Birds not up eating and drinking can lead to poor performance in weight gain and feed conversion. In cases like this, I do my best to look at my air speed, especially in a tunnel house, to see what my potential real feel might be. In most cases, especially on turkeys less than 12 weeks of age, I will likely slow air speed to try to “warm birds” or make them feel more comfortable.

I especially see this situation in brooder houses or even finishers where circulation fans are used to move air off the ceiling to create a uniform environment throughout the house. I like to take a smoke generator, light it, and place it on the floor to see if I am creating a draft, especially with young birds (see the picture below).

If my goal is to move air off the ceiling and create a uniform environment, the smoke plume should rise slowly above the birds and spread out evenly. If the plume bends at floor level, as in the case with this picture, there is a good chance I am creating a draft that is making the real feel of the bird too cool, which is uncomfortable. Birds typically react by sitting in groups around the house, leading to inconsistent feeding and drinking habits, which usually lead to enteritis if this persists for extended periods of time.

We can also overdo air speed over birds in naturally ventilated houses. Recently, I was in a naturally ventilated brooder house with this exact situation. Outside temperature was 84°F and inside was nearly the same. But, there was a stiff breeze blowing through the curtain opening and open-end doors across the floor where the 14-day old birds were residing. Think about this – at 600 fpm that’s 6.8 miles per hour. If we have wind gusts blowing through a house at that rate, what are we doing to a 14-day old bird??? He probably feels a lot cooler than the 85°F the thermometer or controller reports.

The table bottom left is an example of a basic controller set up that incorporates minimum, natural and gradual tunnel applications for turkeys that are around 12 weeks of age. Notice that the controller will be able to handle temperatures that are cold with timer fans running in minimum ventilation. It transitions to negative pressure ventilation when the outside air warms up and inside temperatures move through the 60’s. When the inside temperature reaches 73°, the house converts to tunnel ventilation at a low speed and gradually increases as the house warms. The Effective Temp column shows the approximate/estimated effective temperature that the bird ‘feels’ due to the wind speed as it increases. Notice that the birds remain in the 55-75°comfort zone, even though the actual temperature in the house is as high as 81°.

The picture of the Kestrel air speed tool shows the airspeed in the house. Many times we have house controllers set up to do what we think they are doing, but without measuring, we really don’t know. If I have a house set up to give me 600 fpm (feet per minute) maximum when I have 19 week old toms in 100° heat, I better make sure it is doing that. At the same time, as in the controller set up for younger birds above, I don’t want to get too much air speed too quickly or I will chill the birds. When this happens they sit tight to the floor and do not get up to eat and drink. This leads to several problems – enteric issues, poor weight gain and feed conversion. 

Paying Attention to Detail is a constant challenge. Keeping birds comfortable in all weather conditions is possible if we have our houses set up to be able to handle cold, mild and hot weather. So, the message is this – pay attention to air speed. It can be our friend when it’s hot and we have older birds. It can be our nemesis when it’s cooler out and we have younger birds.

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John Menges

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