XI.—Studies in Embryonic Mortality in the Fowl. II. Chondrodystrophy in the Chick

Abstract

1. Among 7135 chick embryos of nine days or over, obtained from unhatched eggs from three poultry farms, 112 cases of chondrodystrophy were observed. From 1900 eggs set at this Department, 124 chondrodystrophic embryos were obtained.2. The mortality caused by this condition varied in different flocks from 0.80 to 7.96 per cent. of the embryos dying after the eighth day; at this Department it was responsible for loss of 6.5 per cent. of the eggs set.3 The incidence of chondrodystrophic embryos was found to be greatest in January and February, and to decline steadily thereafter to an almost complete absence in June.4. The occurrence of chondrodystrophy appears to be independent of breed of fowl, sex of embryo, and age of dam.5. The number of these abnormal embryos produced by individual hens ranged from 1 to 28.6. Evidence is advanced in support of the theory that the causal agency is an hereditary physiological abnormality in the dam which, under certain unfavourable conditions, results in the production of chondrodystrophy in the embryo.7. It is shown that the incidence of chondrodystrophy appears to be inversely proportional to the amount of sunshine, and the suggestion is made that lack of direct sunlight is a factor in the etiology of the abnormality.