Adaptive behaviour in chickens in relation to thermoregulation

Based on genetically predisposed patterns, behaviour allows rapid reactions towards environmental and internal stimuli with high response plasticity. Among adaptive behavioural and physiological reactions of fowl, thermoregulation is well investigated for its importance in poultry production. In the context of thermoregulation, plumage plays an important role due to its isolating capacities. Several studies showed that a modified feather cover (e.g., through the major genes Na or F) can increase heat tolerance in chickens. The present studies were designed to investigate into behavioural thermoregulative adaptation to heat. In the first study details of the chicken plumage were studied by infrared thermography to investigate possible thermal windows suitable for heat dissipation and their relation to behaviour. In addition to the unfeathered parts such as head and legs, there exist thermal windows within the plumage cover, in particular through the nearly bare areas (apteria) under the wings and the body sides. Adaptive behavioural patterns involving preening, feather ruffling, dustbathing, and conductive heat loss via sitting are used by the bird to expose or close these thermal windows with flexibility. In experiment 2, plumage of the birds was manipulated and the behaviour under short term heat stress was studied. Twenty-four female broiler breeders were kept in floor pens from 19 wk of age at constant temperatures of 20 degrees C (control) or 28 degrees C (heat). At 39 wks of age they were subjected to short term heat challenges at 28 degrees and 32 degrees C for 10 min. The latency until panting and rectal temperatures before and after the test was measured. In half of the birds (N=24) the neck plumage was sheared and birds were re-tested at 40 Wks. Hens housed at high temperatures had reduced heat tolerance as shown by more rapid onset of panting and higher body temperatures. Number of birds panting was significantly reduced in sheared birds, underlining the adaptive role of behaviour. But in all, shearing of the neck revealed only minor beneficial effects during short term heat exposure. However, the comparison of sheared hens with Naked neck genotypes is only partly valid, because the Na gene acts as major gene affecting not only the plumage distribution but also other characteristics.