Stress problems due to environmental changes in captive slender lorises (Loris tardigradus)
In slender lorises, even slight
changes of their environment cause excitement. Stress after transfer to
unfamiliar surroundings may lead to gastric ulcera, fatty liver, inanition
and death. Reduced food consumption is the most reliable sign of stress.
Behaviour may be misleading; some animals during severe stress make an
unusually tame and quiet impression. Noise seems to be a particularly dangerous
stressor. Susceptibility to environmental stress can be reduced by habituation.
High cages with sufficient horizontal branches in the upper part and some
hideaways are also helpful.
In the past, mortality of slender lorises in captivity was high; according to Bertram (1984), for instance, mean longevity of eight captive-bred slender lorises was one year, and Hill (1935) kept his animals (n = 50) alive "up to two years"; slender lorises can reach an age of more than 14 years (some of our wild-caught animals). In our breeding project, some cooperating zoos had severe losses in quarantine. We came to the conclusion that keeping of slender lorises, with regard to diet and climate, is rather easy, but that psychic stress is highly dangerous for this excitable species.
Since Cannon (1935) and Selye (1956), the word "stress" is used for physiological responses to endogenous or exogenous agents, serving to maintain the dynamic steady state of viability. Changes, for instance, of heart rate, blood pressure and secretion of endocrine glands, prepare the body for reactions on stressors such as cold, heat, restraint, perception of threat or sexual stimuli. Consequently, stress is a normal state of life, not necessarily connected with suffering, and has positive effects on health and well-being as long as the stressors remain within certain species-specific limits. Selye, therefore, used the terms "eustress" for adaptation processes with desirable effects and "distress" for pathogenic reactions.
stress (see also figures showing behavioural
signs of stress and facial
In lorises, movements under normal circumstances look flowing and easy, but in emotion-arousing situations become tense, very slow, hesitant or jerky. Freezing to immobility, flight from the source of disturbance and attempts to hide are frequent even after minor disturbance. When the animals are scared, they usually flee upwards until further ascent is stopped by the ceiling of the cage. Sometimes they remain there, hanging upside down, frozen in sometimes unusual postures or hiding their faces, for a considerable time; after severe disturbance some animals even slept in this position. In calm animals, relaxed postures are frequent, for instance during resting and comfort behaviour; under stress they are absent. In situations causing severe stress animals may give a normal and quiet impression. In three cases, when we tried to catch shy animals, they began to appear unusually tame and quiet, made no attempts to flee when touched, and then suddenly had a convulsive seizure; others became apathetic for several seconds after being caught. Seizures occurred in stressful or exciting situations and were triggered by an additional stimulus, for instance by a noise or a sudden change in light intensity. Most of the seizures had the shape of epileptic grand mal (rhythmic convulsions, foam and saliva dripping from the mouth), one resembled feigning death, a protective reaction which might be closely connected to epileptic seizures (Rabe 1970). Reduced food consumption turned out to be the most reliable measure of stress and disease, but may not be noticed when the animal is caged together with others.
In general the animals recovered quickly from short periods of stress followed by stay in quiet familiar environment; no disease or death is known to have been caused by such events. Some animals, however, after handling or other apparenly traumatic events remained shy for years.
Causes of death in adult slender lorises in the two colonies at Ruhr-University and Lennestadt between 1980 and 1993
Practical recommendations for transfer of animals to other facilities
Prophylactic measures against stress before transportation to a new environment:
Measures in the new
environment after transfer
After transfer to an unfamiliar environment lorises need a good protecion from any avoidable disturbance (noise, visibly moving larger objects or persons); the fronts of their cages ought to be covered for instance with blankets. Small holes for observation apparently cause little stress because the perceived stimulus does not look large; even stressed animals approached the holes and looked through them into the observer´s eye from short distance. Cages containing plenty of cover (artificial plants) help the animals to feel safe and recover soon.
Dim light during daytime in the first days in an unfamiliar environments may be useful because the animals feel safer in darkness (according to Perret, 1982, in Microcebus a reduction of daylength had a protective effect against diseases caused by stress). At least some food ought to be offered in a protected, high place the animals are not too afraid to approach. Change of diet under stress conditions ought to be avoided as some animals already under usual circumstances hesitate to try new food and during stress may refuse eating. Moving insects (locusts, mealworms) may encourage shy animals to eat and seem to improve their psychic state.
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