Lipid and energy metabolism in chicks affected by dwarfism (dw) and Naked-neck (Na).

In two experiments, sister pairs of chicks, one dwarf (dw) and one nondwarf (Dw+), were reared in individual cages to 5 weeks of age. Chicks carrying the sex-linked recessive dw gene were identified at hatching by the closely linked fast feathering gene (k). The dwarf chicks showed a 27% reduction in weight gain, a reduced body temperature, increased carcass content of lipid, and increased lipid 14C activity from injected 14C-labeled acetate. The augmented accumulation of carcass lipid in the dwarf chicks was shown to be a result of increased lipogenesis and decreased energy expenditure. An autosomal dominant gene for naked-neck (Na), present in half of the pairs of chicks, also caused increased lipogenesis. Naked-neck birds showed increased energy expenditure in a cool environment and perhaps a greater flexibility of body temperature regulation. An interaction between the dw and Na genes was apparent under cool environmental conditions and may have been due to a suppression by the dw gene of the Na gene's effect on thermoregulation, possibly by slowing down lipid degradation.