Effects of the naked‐neck gene on traits associated with egg laying in a dwarf stock at two temperatures

Abstract

1.	Naked‐neck (NaNa and Nana+ ) and normal hens, all dwarf (dw), were compared for laying performance in two groups at 15 to 20 or 30 °C.
2.	Naked‐neck hens, especially homozygotes, weighed less only at the cooler temperature. Body fatness was not different.
3.	Normal, but not naked‐neck birds, showed a depression in food intake and egg output at 30 °C. In the hot environment mean egg weight and egg mass output were highest for naked‐neck homozygotes. At the cooler temperature mean egg weight was also higher for this genotype, at fixed body weight.
4.	The decline in egg mass with time seemed greater for fully‐feathered layers at high temperature.
5.	At moderate temperature residual food intake was slightly increased by the naked‐neck gene, but owing to the reduced body weight, food utilisation was not poorer for the NaNa or Nana + genotypes. At higher temperature Nana + and especially NaNa hens utilised food more efficiently.
6.	An increase in wattle size and a slight decrease in body temperature were associated with the Na allele.