Sensory reinforcement and illumination preference in sheep and calves.

The preferences of sheep or calves for light or darkness have been examined by placing animals in light-proof chambers in which they could turn the lights on or off by interrupting an infrared beam switch with their muzzles. Sheep spent an average of 77% of each 24 h period in light while the calves spent an average of 67% of each 24 h in light. The experiments show that sheep and calves prefer light to darkness. The strength of their motivation for light was examined by means of an operant task in which they were rewarded with only 40 s of light for each interruption of the i.r. beam. Sheep then obtained an average of 1.5 h of light per 24 h and calves 1.0 per 24 h. Finally, the animals were subjected to a situation in which the light only remained on for as long as the i.r. beam was interrupted. In this experiment sheep obtained 4.8 min of light per 24 h and calves 3.2 min per 24 h. Quantitative operant methods can provide an objective means for measuring environmental preferences in farm animals.