1. Visual acuity of cattle determined by the method of discrimination learning;Entsu;Appl. Anim. Behav. Sci.,1992
2. Individual recognition and the dominance hierarchy in the domesticated pig. The role of sight;Ewbank;Anim. Behav.,1974
3. Reference Manual, Release 6.1;GenStat,2002
4. Graf, R., 1976. Das visuelle Orientierungsvermögen der Schweine in abhängigkeit von der Beleuchtungsstärke. In Instituut Voor Veeteeltkundig Onderzoek, Zeist, p. 56.
5. Livestock behaviour as related to handling facilities design;Grandin;Int. J. Stud. Anim. Prob.,1980