1. Bean, D., Mason, G.J., Bateson, M., 1998. Why do animals work for food when food is free? Using starlings to test the information hypothesis for contra-freeloading. In: Proceedings of the 32nd Congress of the ISAE, Clermond-Ferrand, France, p. 107.
2. CVB, 1999. Voedernormen landbouwhuisdieren en voederwaarde veevoeders. Verkorte tabel. CVB-reeks nr. 26.
3. Effects of environmental enrichment on behavioural responses to novelty, learning, and the circadian rhythm in cortisol in growing pigs;De Jong;Physiol. Behav.,2000
4. The circadian rhythm of cortisol in the saliva of young pigs;Ekkel;Physiol. Behav.,1996
5. The effects of mixing upon behaviour and circadian parameters of salivary cortisol in pigs;Ekkel;Physiol. Behav.,1997