The functional significance of stereotypies in the stabled horse.
Surveys were conducted to determine the prevalence of weaving, cribbiting/
wind-sucking, box-walking and wood-chewing in Thoroughbred
racehorses and performance horses. Logistic regression analysis showed that
increases in the prevalence of abnormal behaviour on Flat and National Hunt
training yards were associated with feeding small amounts of forage, the use of
bedding types other than straw and box designs that limited contact between
neighbouring horses. Increased prevalence of abnormal behaviour among
eventing and dressage horses was positively correlated with time spent in the
Videofluoroscopic and endoscopic studies, conducted on crib-biting horses,
showed that deglutition was not involved in this behaviour and that air
distending the cranial oesophagus did not elicit peristalsis. Behaviour and
nutritional studies showed that unthriftiness in crib-biters may occur, if planes of
nutrition are critical, because these horses expend energy performing the
behaviour while spending less time resting and nourishing themselves.
Crib-biting showed a post-inhibitory rebound suggesting that an internal
motivation to crib-bite rises during periods of deprivation. This suggests that
mechanical or surgical attempts to prevent crib-biting may compromise the
welfare of stereotypic horses.
The adaptation of two techniques from human gatro-enterology (radiopaque
markers and sulphapyridine uptake) identified physiological differences
associated with crib-biting including diet-dependent changes in total gut and
foregut transit times. Gut motility was also affected by the short term deprivation
of eating and crib-biting together. The behavioural and physiological
consequences associated with depriving horses of crib-biting were also assessed
using heart rate monitors, behavioural sampling and plasma levels of cortisol and
beta-endorphins. Although crib-biting did not affect circulating beta-endorphin
levels, elevated plasma cortisol levels were found when crib-biting and eating
were prevented. It is suggested that crib-biters are more stress-susceptible than
normal horses because their cortisol levels were elevated before and during short
periods without food and crib-biting substrates.