1. Brownlee, A., Ewbank, R., Fox, M. W. & Hart, B. L. (1966) Annual Report of the British Veterinary Association, p. 73.
2. Study of the quality of free-range and laying battery hen eggs with particular reference to baking
3. Glister, G. K. (1966) Personal communication.
4. The Behaviour of Domestic Animals;Hafez,1962