Temperature Control

The layer industry uses air exchange and air velocity in designing ventilation systems to control temperature. In addition, the thermal neutral zone upper limit has been expanded to 85°F (29°C) in older flocks that are producing heavier eggs (Table 1). This higher temperature means that the hens consume less feed and require less energy to maintain their body temperature and productivity. Precise environmental temperature control enhances the hens' ability to regulate sensible and insensible heat loss and cope with the higher temperatures used by

Temperature (F) Sensible Heat Loss -■- Insensible Heat Loss

Fig. 3 Sensible (conductance) and insensible (evaporative) heat loss from birds as environmental temperatures increase. (Figure courtesy of Ref. [8].) (View this art in color at www.dekker.com.)

producers.[6] Heat loss by the birds gradually shifts from sensible (conductance) heat loss during the cool seasons to insensible (evaporative), as the ambient environmental temperatures increase in the summer (Fig. 3). Air exchanges regulate temperature, humidity, dust, and ammonia throughout the year to keep the hen in the range of sensible heat loss mechanisms. This provides for improvements in feed conversions since the hen requires fewer calories for body temperature homeostasis, thereby releasing energy for egg production. Air velocity is important during the hot season, because environmental temperatures can exceed 85°F (29°C). Insensible heat loss methods require more energy input by the hen because of panting, resulting in depressed feed consumption, reduced egg size, and subsequently reduced production. However, air velocity increases the sensible heat loss capabilities of the hen via a wind chill effect, which helps maintain the balance between sensible and insensible heat loss. The development of highly nutrient-dense diets has been key for the utilization of higher environmental temperatures, using the upper limits of sensible heat loss methods so the birds can optimize feed conversion.

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