Sexing on down and feather colour in the Dandarawi Egyptian breed.

1. The study was on a population of the Egyptian local strain Dandarawi. Hatching records were obtained from three lines over two generations (1996 and 1997). Sex ratios were calculated using a total of 5,822 1-d-old chicks. 2. Sex could be identified at hatch by down colour. Female chicks showed a black spot on the head or irregular strips on the back, whereas males had no marks on head and back. At 8 weeks of age, progeny could be easily sexed by feather colour, which was black and white for males and brown for females. The sexual dimorphism in feather colour at that age is due to the presence of the autosomal recessive wild type allele CO*N. Accuracy for autosexing at hatching time was 89-02% for males and 92-42% for females. 3. Sex ratio deviated significantly from the expected value, 1:1, in one line (line E) where the number of female chicks exceeded that of males, over the two generations. Chicks of both sexes exhibited the same survival rate up to 8 weeks of age.

Genetic variation in susceptibility to Marek's disease in a commercial broiler population.

Two commercial broiler pure lines that were previously identified to differ in their susceptibility to Marek's disease (MD) were line-crossed to generate an F1 population. Eight F1 males were randomly mated to four or five F1 females to produce an F2 test population that would be segregating for genes affecting MD. All F2 progeny (four hatches) were pedigreed at hatch and placed in colony houses as nonvaccinated. At 5 days of age, they were challenged intraabdominally with MD virus RB1B. Clinical signs, mortality, and gross and microscopic lesions were recorded during the MD challenge. At 8 wk postchallenge, all remaining birds were euthanatized and necropsied. During the MD challenge of the first two hatches, we observed that several severely stunted broilers originated from certain families and the differences in body weight among birds appeared as early as 3 wk postchallenge. To confirm this observation, body weight at 6 wk postchallenge was determined for all surviving birds in hatches 3 and 4 (n = 242). Genetic variation in body weight among broiler sire families was apparent; the average body weight for males at this time was 2.07 kg, whereas with females, it was 1.87 kg. At least 12.2% of the broilers, including both sexes, weighed less than 1 kg ("severely stunted") at this time. The incidence of these growth-stunted birds within each broiler sire family ranged from 0 to 26% and for dam families, 0 to 60%. Correlation analyses between stunting and other MD-associated traits revealed that the incidence of stunting had a significant and positive association with paralysis (r = 0.50). Therefore, the data suggest that there may be a genetic component affecting body weight loss during MD infection. The genetic component is speculated to affect susceptibility to MD paralysis with an indirect effect on the body weight of birds. The significance of this finding is best exemplified by the identification of a broiler sire family with over 26% of its progeny affected by this MD-associated trait.