Abstract:
The productive performance of major genes for feather reduction (naked neck and frizzle) and body
size reduction (dwarf) in a dual-purpose layer strain was evaluated in the subtropical coastal region of
southeast Africa (Maputo, Mozambique). The experimental material consisted of eight different genetic
groups, two diets (14.4 and 16.2% crude protein) and two climatic seasons. Birds were caged individually in
a laying house with natural light and ventilation. Traits measured were: temperature and relative humidity,
body weight, age at first egg, egg number and weight, feed intake and mortality. The following were
calculated: persistence, egg mass, feed efficiency, feed conversion, biological efficiency (EMD/BW0.75) and
productivity (EN/BW0.75). The main results show that: (1) none of the feather-reducing genes significantly
improved egg production or feed efficiency, although the naked neck (Na) excelled in terms of biological
efficiency and productivity; (2) the dwarf gene (dw) was associated with delayed sexual maturity, production
of fewer and lighter eggs, higher persistence, better feed conversion and higher survivability; (3) elevated
temperatures restrained voluntary feed intake, egg number and weight, and body weight gain; (4) the lower
dietary protein content resulted in decreased body weight. It was concluded that the genes were not equally
responsive to the environments, which offers the opportunity for selective breeding
