| dc.description.abstract | Two putative functions of equine stereotypies (crib-biting and weaving) were
proposed: 1) `behavioural need', the behaviour substitutes an unobtainable
consummatory behaviour (e. g. eating); 2) `reward function', the behaviour
counteracts the physiological effects of a stressor.
Several hypotheses were established to test these putative functions within one
experimental design. This experiment measured the physiological (heart-rate, plasma
cortisol and plasma beta-endorphin) and behavioural responses to performing and
preventing equine stereotypies (using the crib-strap and anti-weave bar) in cribbiting
(n=4), weaving (n=3) and control horses (n=4). The behavioural effects of
administering an opiate antagonist (naloxone) to these horses were also assessed.
Results indicated that Hypothalamo-pituitary-adrenal (HPA) activity (plasma
cortisol) was significantly higher (p<0.05) immediately prior to the onset of
stereotypy followed by a significant reduction and suggested that both crib-biting and
weaving function as a `reward function' to reduce stress levels in the animal and not
as a `behavioural need'.
The crib-strap significantly elevated (p=0.05) mean plasma cortisol in crib-biting
horses and a similar trend (p=0.07) was observed for the weaving group during the
anti-weave bar treatment. Both crib-strap and anti-weave bar significantly elevated
(p<0.05) plasma cortisol in the control horses. The continued performance of
stereotypy during these prevention treatments and the significant physiological
changes recorded for the control horses prevented a definite conclusion being drawn
with respect to the hypotheses being tested. The results, however, did suggest that the
use of the crib-strap and anti-weave bar are stressful to horses and thus may be a
welfare concern.
The opiate antagonist naloxone significantly reduced crib-biting by 84% (p=0.07) but
not weaving (p=0.37) indicating that the former but not the latter of these stereotypies
functions as a reward behaviour. However, resting behaviour was also significantly
increased (p=0.02) in crib-biting horses suggesting that the reduction in stereotypy
was due to a sedative effect of the opiate antagonist. However, since the effect was
not measured in control or weaving animals these results may be interpreted
differently.
Finally, plasma beta-endorphin and prolactin (as an indicator of central nervous
system [CNS] dopamine activity) levels were not significantly different between
stereotypy and non-stereotypy horses. The development of equine stereotypy cannot,
therefore, be attributed to substantial differences in CNS opioid or dopamine
physiology. However, the low numbers of experimental animals used in this study
requires that these results be interpreted with caution. | en |
