Relationship between plasma cortisol and stereotypic activities in pigs

The relationship between the performance of post-feeding stereotypic behaviour and plasma cortisol levels and the effect of prevention of stereotypic behaviour on plasma cortisol levels were studied in chronically restrained sows. In experiment 1 sows classified as high or low stereotypers on the basis of time spent manipulating chain and behaviour directed to the nipple drinker were found not to differ in plasma cortisol levels. Removing the chain and nipple drinkers also did not affect cortisol concentrations of either group. In experiment 2 detailed recordings were made by an automatic logging system of two major categories of stereotypy; chain manipulation and drinking. There were large individual differences in levels of both chain manipulation and drinking. Both activities showed a similar diurnal pattern, but average levels across individuals were not correlated. Both activities showed a continuous distribution across individuals and therefore a correlational rather than factorial analysis was used. Chain manipulation was not correlated to cortisol concentrations on any of the control days and removing the chain for one day (experiment 2A) or for seven days (experiment 2B) was also not accompanied by increased cortisol levels. However individuals showed a consistent cortisol response to chain removal as indicated by correlations between treatment days. Drinking showed a tendency to be negatively correlated to cortisol concentrations on control days. Long-term chain removal was accompanied by an increase in average drinking that showed a non-significant tendency to be negatively correlated to plasma cortisol on treatment days and thus may explain part of the consistency of response to chain removal. The lack of correlation between chain manipulation and plasma cortisol suggests that this activity does not serve to reduce plasma cortisol in chronically restrained sows. The relationship between drinking and cortisol need not necessarily reflect the coping capacity of this behaviour but may be a physiological consequence of the large amounts of water ingested.