1. Duncan, I.J.H. and Petherick, J.C., 1991. The implications of cognitive processes for animal welfare.Journal of Animal Science, 69, 5017–5022
2. Duncan, I.J.H. and Fraser, D., 1997. Understanding animal welfare. Cap. 2. In: M.C. Appleby and B.O. Hughes (eds), Animal Welfare(CAB International, Wallingford, Oxon, UK)
3. Griffin, D.R. and Speck, G.B., 2003. New evidence of animal consciousness.Animal Cognition, 7(1), 5–18
4. Hampton, R.R., 2001. Rhesus monkeys know when they remember.Proceedings National Academy of Science of the United States of America, 98(9), 5359–5362
5. Primatt, H., 1776.Dissertation on the Duty of Mercy and Sin of Cruelty to Brute Animals(R. Hett, London); II edn. London 1832; III edn. Edinburgh 1834; ultima edn. T Constable 1934, p. 63