I.C. de Jong

Coping styles in animals: current status in behavior and stress-physiology

This paper summarizes the current views on coping styles as a useful concept in understanding individual adaptive capacity and vulnerability to stress-related disease. Studies in feral populations indicate the existence of a proactive and a reactive coping style. These coping styles seem to play a role in the population ecology of the species. Despite domestication, genetic selection and inbreeding, the same coping styles can, to some extent, also be observed in laboratory and farm animals. Coping styles are characterized by consistent behavioral and neuroendocrine characteristics, some of which seem to be causally linked to each other. Evidence is accumulating that the two coping styles might explain a differential vulnerability to stress mediated disease due to the differential adaptive value of the two coping styles and the accompanying neuroendocrine differentiation.

Effects of environmental enrichment on behavioral responses to novelty, learning, and memory, and the circadian rhythm in cortisol in growing pigs

Previously we showed that pigs reared in an enriched environment had higher baseline salivary cortisol concentrations during the light period than pigs reared under barren conditions. In the present experiment, it was investigated whether these higher baseline salivary cortisol concentrations were a real difference in cortisol concentration or merely represented a phase difference in circadian rhythm. The effects of different cortisol concentrations on the behavioral responses to novelty and learning and long-term memory in a maze test were also studied in enriched and barren housed pigs. At 9 weeks of age enriched and barren housed pigs did not differ in baseline salivary cortisol concentrations nor in circadian rhythm, but at 22 weeks of age barren housed pigs had a blunted circadian rhythm in salivary cortisol as compared to enriched housed pigs. The differences in baseline salivary cortisol concentrations between enriched- and barren-housed pigs are age-dependent, and become visible after 15 weeks of age. Enriched- and barren-housed piglets did not differ in time spent on exploration in the novel environment test. Barren-housed pigs had an impaired long-term memory in the maze test compared to enriched-housed pigs; however, no differences in learning abilities between enriched- and barren-housed pigs were found. Because blunted circadian cortisol rhythms are often recorded during states of chronic stress in pigs and rats or during depression in humans, it is suggested that the blunted circadian rhythm in cortisol in barren-housed pigs similarily may reflect decreased welfare.

Mixing induces long-term hyperthermia in growing pigs

The purpose of this experiment was to determine whether body temperature is a sensitive parameter to measure long-term effects of stress in pigs. Mixing of unacquainted pigs is a severe stressor that has detrimental effects on health, production and welfare. We measured deep body temperature after mixing growing pigs. Five pigs of 15 weeks of age, each individually housed with a companion pig, were mixed with two unacquainted congeners. Deep body temperature, heart rate and activity were recorded by radiotelemetry 9 days prior to until 8 days after mixing. These parameters were also recorded in dive control pigs (individually housed with a companion pig) during the same time span. Behaviour during the light period was recorded on videotape on the day of mixing and on three subsequent days. Mixing induced a significant rise ill body temperature that lasted for 8 h after mixing. Although heart rate and general activity level did not significantly differ between mixed and control pigs, mixing significantly increased the frequency of fighting and reduced the frequency of earing. In conclusion, the present experiment shows that mixing induces a long-lasting hyperthermia in pigs. Thus, deep body temperature may be used as a sensitive parameter to measure long-term effects of stress in pigs.

Measuring foot-pad lesions in commercial broiler houses. Some aspects of methodology

For monitoring purposes there is a need for a protocol to measure foot-pad dermatitis (FPD) on-farm. Therefore, we studied the effect of number of birds sampled, number of locations sampled and sampling location in a broiler house on the accuracy of measurement, in order to construct a protocol that can be applied in practice. Samples were taken from eight commercial flocks (Ross 308) at up to ten locations with up to 25 birds sampled per location. Foot-pad lesions were scored in all birds for both feet using the Swedish scoring method. No significant differences in FPD score were found between the first five birds and all birds sampled at a particular location. Although locations near the walls did not differ in FPD score from locations in the central area of a house, the severity of foot-pad lesions was unevenly distributed over the house. A model was constructed showing the inaccuracy related to the number of locations sampled in the house and the number of birds sampled per location. The model shows that in situations with at least five locations differences in inaccuracy are relatively small when a total of 100 birds or more is sampled. Inaccuracy is largest in a flock with variation in foot-pad scores, as compared to flocks with little variation. The results of this experiment can be used to determine the optimal sample size in a commercial broiler house.