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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.

Behaviour indicating stress (see also figures showing  behavioural signs of stress and facial expressions)
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

Transfer to a new environment (other institutions or quarantain stations) was the most frequent cause of death in the slender lorises from Ruhr-University. Post mortem examinations of eight animals showed inanition, fatty liver degeneration, liver necroses and/or gastric ulcers, symptoms which may be caused by psychic stress (Näätänen, Hopsu 1955; Perret 1982). An infection with Staphylococcus albus, found in one case, might have been secondary; in all other cases no evidence of infections or other diseases were found.
Similar cases are described by other authors: Manley (1966) reported that five of eight deaths in slender lorises from the Zoological Society of London's prosimian collection were caused by stress, resulting in bleeding gastric ulcers and inanition, and according to Osman Hill (1942) the female of a pair of L. t. nycticeboides "suddenly collapsed" a week after arrival; the male died of hepatic disease one week later.
After some transports 50 - 75 % of our animals died, others did not lead to losses. The rate of deaths was not correlated with the duration of transport. In one case the quarantaining zoo reported that, for unknown reasons, four animals became sick during flight, showing a very yellow skin colour on arrival; three of them died in quarantine.

Practical recommendations for transfer of animals to other facilities

Prophylactic measures against stress before transportation to a new environment:

Transport
For transportation, at Ruhr-University we boxes with some protection against bright light (slots which still leave plenty of fresh air in) were built. Sufficient supply with fresh air may reduce oxygen deficiency in cases of cardiac or respiratory trouble because of distress. The transport boxes usually were large enough to avoid restraint stress, with some round branches to which they could cling and some artificial plants. Transport in very narrow boxes by other facilities, however, did not cause visible health problems. Particularly if tranquilizer is used, danger of lesions must be considered because of slower reaction and possible equilibrium problems of the animals. The animals at Ruhr-Unversity are not handled before transport, but allowed to enter the crate through a wiremesh passage or caught in cage traps and allowed to enter the crate from there. Of course no hammer and nails are used for closing boxes.

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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