1 Zootechnical Institute, University of Milan, Milano, Italy 2 Department of Animal Nutrition, Genetics, Production and Ethology, University of Ghent, Merelbeke, Belgium
A percentage of horses in captivity perform unvarying repetitive behavioural patterns with no obvious goal, which can be defined as stereotypies (Kiley-Worthington, 1977), well described by several authors (Cromwell-Davis, 1986; Houpt, 1981; Sambraus, 1985). It can be concluded that when these behaviours are performed during a substantial percentage of active time something wrong has occurred in the housing or the management of such horses. Nevertheless, some stereotypies seem to have benefits as substitutes for the normal behaviour patterns or they may have more general roles in helping the animal to cope with stressful situations (Mason, 1991). The homeostatic hypothesis finds some support when they are associated with reduced physiological responses often associated with arousal of pituitary-adrenocortical activity or heart rate (Ödberg, 1989; Saussignan & Koch, 1985; Schouten & Wiepkema, 1991) and reduce the chances of development of psychosomatic complications such as stomach ulcers (Wiepkema et al., 1987).
The aim of this study was to determine if, within the same individual, heart rate values recorded while the subject is stereotyping are significantly different from heart rates recorded during other behaviours. In another study not reported here, the reactions of cribbing and non-cribbing horses to standardized stimuli were compared.
Basal recordings of behaviour and heart rate have been taken in 8 adult saddle horses, 5 geldings and 3 nonpregnant mares, with no clinical signs of cardiac disease. All of them were long-time crib biters. Heart rate was recorded with the Polar Electro PE-3000 meter adapted with a special girth belt for horses. A Psion Organiser LZ64 portable computer, loaded with The Observer 3.0 software, was used for the behavioural observations. Integrated analysis of heart rate signals and observational data was carried out with the same program. Four recordings lasting 30 min each were were taken during different days.
Heart rate showed a great variability between horses during cribbing but not between the four recordings. This indicates a relatively constant heart rate during the stereotypy within each individual. Heart rate was statistically lower when horses were cribbing than during all other behavioural patterns (p<0.02). Heart rate often rose a few seconds before cribbing bouts and decreased once cribbing had started. One can speculate about the similitude between this phenomenon and the parasympathical stimulation induced through the Valsalva manoever in tachicardic patients.
These preliminary findings seem to support the homeostatic function hypothesis of some stereotypies in some species.
References
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