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Andrew M. Janczak- abstract fra doktorgradsavhandling
Ane Gro Siri SkjelfjordAbstract fra avhandlingen
Fear, anxiety and coping styles: Validity and implicatons for maternal ability in pigs (Dr. agric)
The primary focus of this thesis was to investigate the validity and predictive value of hypotheses describing the behaviour of pigs in terms of fear, anxiety, fearfulness and coping styles, and to test for implications of individual variation in validated measures of coping-related behaviour for maternal ability in sows. It is frequently suggested that domesticated animals have the ability to express all the forms of behaviour observed in their wild counterparts. Although it may not be true, this assumption underlies current approaches to the study of farm animal behaviour. The present thesis therefore tested for effects of selection for large litter size on the ability of mice to show functional coping responses by comparing a randomly selected mouse strain to a strain selected over many generations for high litter size. Contrary to widely held beliefs, the results from mice indicated that selection for production traits in animals may reduce the ability of domesticated species to show certain forms of functional behaviour in challenging situations. Furthermore, one-sided selection appeared to have altered the thresholds at which the animals reacted to aversive stimuli and disrupted otherwise adaptive patterns of coping responses. The findings in mice suggested that animals selected for production traits may become better adapted to specific potentially stressing stimuli in their stable production environments, but may have more difficulty than wild-type animals in coping with more unfamiliar forms of environmental challenge and variation. It is suggested that further research on coping-related behaviour in farm animals should more precisely define the stimuli with which animals are challenged and the context within which observations are made, as well as considering the potential implications of artificial selection in a specific production environment.
Because experiments investigating the validity of traditional models of fear and anxiety in pigs are widely lacking, the validity of selected behavioural tests was investigated. This was done both to increase the current understanding of existing models and to investigate the applicability of new models for studying anxiety-related behaviour in pigs. The results indicated that the traditional open field, and more seldom-used light/dark tests do not allow separate identification of activity- and anxiety-related behaviours. A porcine elevated plus-maze similar to that used in rodent studies, on the other hand, was found to be useful in obtaining separate measures of anxiety and activity. A modification of the described apparatus may in the future prove useful in basic or more applied research on anxiety-related behaviour in pigs. It is suggested that all currently used models of fear and anxiety in pigs should be subjected to more stringent validation within the conceptual framework applied in investigating the validity of the porcine elevated plus-maze. Such methods applied within a sound theoretical framework would greatly increase the validity of conclusions drawn on the basis of experiments using tests of fear and anxiety in pigs.
Because the main goal of the thesis was to use validated measures of coping styles, fearfulness, fear and anxiety for predicting the maternal ability of sows, the validity of these concepts were tested within a framework emphasising stimuli likely to stress farmed pigs, thereby adversely affecting their maternal ability. In studying the responses of weaned growing pigs and gilts to conspecifics, humans and a novel object in a novel arena, measures of fear of humans, novelty-induced anxiety and aggression were found to have some repeatability between ages. This indicated that responses to specific stimuli at an early age were predictive of later responses to similar stimuli, and that such measures should therefore be useful in measuring stable aspects of personality in pigs. However, there was little support for the predictive value of the coping styles hypothesis in pigs. The concept of fearfulness, predicting similar reactions to humans and novelty, was confirmed for young pigs but not for gilts, suggesting that learning and the development of cognitive control of behaviour may override general response patterns as pigs grow older. These findings in pigs reiterate the suggestion made on the basis of studies with mice, calling for more precise definitions of behaviour in relation to stimuli and their context.
Because elevated levels of fear and anxiety are associated with physiological stress responses, and because pigs are regularly or intermittently exposed to humans and novelty, respectively, early responses to humans and novelty were used as predictors of maternal ability. It was found that higher fear of humans observed in 8-week-old pigs was associated with reductions in several measures of maternal ability in sows, but that early responses to novelty were not significantly related to maternal ability. This is suggested to reflect the chronic effects of contact with humans in certain animals, as opposed to putative effects of more infrequent exposure to novelty, again underpinning the independence of responses to different specific stimuli. The associations between fear, maternal behaviour, and piglet mortality suggested that fear of humans may reduce the survival of piglets both during and after farrowing. Variation in piglet mortality may partly be explained by effects of stress on opioid-mediated inhibition of oxytocin secretion during parturition, leading to prolonged farrowing durations, increased numbers of stillborn piglets, and weakening of live born piglets. However, it is suggested that stress-induced reductions in cognitive function affecting attention to piglets may be an important factor influencing the mortality of live born piglets. Because prefrontal cortical and hippocampal mechanisms are involved in the functioning of cognition, further research could investigate the influence of stress in pigs on these regions of the brain, and the implications of their function for maternal ability. In the meantime, it is likely that the development of environmental and genetic methods for reducing fear of humans in pigs would improve the maternal ability of sows and reduce piglet mortality. This would be beneficial for the welfare and productivity of both the sow and her piglets.
Pr. desember 2004:
Andrew M. Janczak, Universitetet for miljø- og biovitenskap, IHA, Postboks 5003, 1432 Ås
Publisert: 01.12.08
Oppdatert: 05.01.09
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