Observations of sows and gilts in tethers, stalls, and groups showed two distinct types of behaviour: pre-feed behaviour when pigs were anticipating food, and after-feed behaviour. Sows and gilts tethered for the first time do not show pre-feed excitement, but this develops in 42 days which suggests that pre-feed behaviour is not stereotype, as suggested by the literature, but is a conditioned reflex.
The question of the importance of after-feeding behaviours which are often called stereotypies is examined. The total time occupied by these behaviours over 24 hours by tethered sows is 14.5 to 29.0%, by tethered gilts 1.4 to 5.6%, by stalled sows 10 to 14%, and 4.2 to 6.3% in stalled gilts.
Grouped animals do not show the same behaviours as the stalled and tethered ones.
Several examples of true stereotypies are described, but not all tethered or stalled pigs exhibit chronic bar biting. Changes in the environment of two of these sows did not alter the fixed stereotype behaviour. Each individual seems to have an optimum level of environmental stimulation which may account for the great differences in individual behaviours.
Blackshaw, J.K., & McVeigh, J.F. (1984). Stereotype behavior in sows and gilts housed in stalls, tethers, and groups. In M.W. Fox & L.D. Mickley (Eds.), Advances in animal welfare science 1984/85 (pp. 163-174). Washington, DC: The Humane Society of the United States.