THERMOREGULATION IN NAKED NECK CHICKENS SUBJECTED TO DIFFERENT AMBIENT-TEMPERATURES

1. Heterozygous (Na/na) naked neck chickens and their normally feather ed (na/na) sibs, were exposed to constant ambient temperatures (Ta) ra nging between 15 and 35 degrees C and 12h: 12h diurnal high:low temper atures of 15 degrees C:35 degrees C. 2. No significant effect of genot ype was obtained in weight gain and food intake. However, the naked ne ck birds tended to gain somewhat more weight at high Ta and consume mo re food at low Ta. 3. At 35 degrees C Na birds showed better regulatio n of body temperature (Tb) and demonstrated considerably higher radiat ion from the neck. 4. The greater food intake of the naked neck chicke ns at 15 degrees C was associated with significantly higher packed cel l volume, haemoglobin concentration, heart and liver size. These appea r to involve both higher heat production and haemodynamic changes to a ccommodate the higher oxygen demands of the naked neck chickens at low Ta. 5. The results indicate the ability of the naked neck chickens, o n the one hand to thermoregulate at low Tas and, on the other their sl ightly better capacity to maintain Tb at high Tas. However, no genotyp e advantage was obtained under diurnal cyclic temperature conditions.