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

• 2 deaths were a consequence of agonistic behaviour from conspecifics.
• 4 animals died or had to be euthanized after showing symptoms of severe diabetes; two of the four animals became sick immediately after fighting in their group in the course of which they had shown signs of severe social stress.
• 1 animal died of a large gastric trichobezoar at the age of more than 15 years.
• 1 death was caused by myocarditis and liver necroses; no transport had preceded this death, and no signs of infectious disease were found.
• 1 animal died from an effusion of blood into the epicard which might have been caused by a chute or by toxic influences.
• No animal died during transport.
• No deaths occurred after transport from one of our colonies to the other, conditions of life being similar in both (n = 28 transfers).
• No losses occurred in animals from other breeders quarantined in our institute (n = 4)
• 13 animals died within 1 - 7 weeks after transport to other institutions or after being moved to a different location within another institution (27 % of n = 48 transfers).
• After cautious habituation of all animals to occasional noise, some environmental changes and human proximity and improved information for the keepers, transports to new breeders with one exception did not lead to further losses (n = 18).

Practical recommendations for transfer of animals to other facilities

Prophylactic measures against stress before transportation to a new environment:

• Cautious habituation of the animals to some environmental change before transport,
• a good comfortable transport crate, habituation of the animals to it
• Offering an adequate diet with sufficient vitamins
• Good preparation by the zoo / quarantain station to which the animals will be brought:
• The interior of new cages ought to resemble the cages they came from (for instance containing natural branches);
• Hideaways in the cages (for instance artificial plants) reduce stress; in the first days after transport additional covering of the cage fronts, for instance with blankets, has proven to be most helpful.

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.
 

Back to the top of this page