SUMMARY
Caged rhesus macaques (Macaca mulatta) were trained to voluntarily enter a transport cage in an attempt to avoid undue distress reactions jeopardizing the validity of research data collected from such subjects. The training program required no extra technical equipment such as cage-squeeze-backs. Patience, gentleness, firmness and a good understanding of the animals were qualities of the animal care personnel ensuring the monkeys' willingness to cooperate. Of 341 trained adult rhesus macaques tested in the course of a routine weighing procedure, 87.4% (298/341) entered the transport cage promptly. Of the animals that were uncooperative, the majority entered the transport cage after encouragement (18/43) or after being prodded with a stick for no longer than 30 seconds (23/43). Only 2 subjects (0.6% of 341) stubbornly refused to leave their home cage and had to be chemically immobilized before they could be removed. Neither cage location (165 animals in lower-row cages, 176 animals in upper-row cages), sex (237 females, 104 males) or housing condition (67 single-housed animals, 274 pair-housed animals) had a noticeable impact on the animals' cooperativeness during the catching procedure.
It was concluded that the time investment in the initial training quickly paid off in predictably swift catching of caged subjects that were not unduly distressed when entering the transport cage.

INTRODUCTION
Caged laboratory macaques have to be caught regularly for routine husbandry and specific experimental reasons. The procedure is often associated with substantial disturbance because the animals resist leaving their homecages. A survey conducted in 1991 of the status of nonhuman primate care and use at the National Institutes of Health revealed that only 22% of investigators transport cage train their subjects so they can move the animals while they are conscious ¹. Animals to be caught are usually driven out of their cages by using force or they are caught by hand after being mechanically or chemically immobilized. In each case, distress reactions are likely to occur. Distress however, is not only an unpleasant experience for the subject but it also jeopardizes the validity of research data collected from it. There are several reports indicating that single-housed macaques can be readily trained to cooperate rather than resist during the catching procedure^2-4. The success of such a training program under routine management conditions has not been evaluated so far. No report has been published on transport-cage-training of pair-housed animals. Recent federal rules require' that provisions be made to address the social needs of laboratory primates⁵. As a result of this, many single-housed animals are being transferred to compatible pair-housed conditions. It would be desirable to apply transport-cage training techniques of single-housed to pair-housed animals. Relatively low success rates, however, are to be expected since pair-housed animals not leave their familiar cage but also their social companion. Pair-housing of rhesus macaques has recently been implemented at the Wisconsin Regional Primate Research Center⁶.All animals had been transport cage-trained while living under conventional single-housing conditions. The present study evaluates the training program and compares its success rate in single-housed subjects with that in pair-housed subjects.

METHODS
All 341 adult (>4 years old) healthy, rhesus macaques (Macaca mulatta) of the Wisconsin Regional Primate Research Center living singly (67 animals exempt from social housing because of special research protocols or veterinary reasons) or in compatible isosexual pairs (274 animals) were the subjects of this study. A total of 176 animals lived in upper-row cages, 165 animals lived in lower-row cages. There were 237 females and 104 males. Single animals were housed in 85 x 85 x 85 cm cages. Paired animals lived in double cages, 85 cm high, 85 cm deep and 170 cm wide. Each cage was provided with a 21 x 30 cm exit and with a sliding door close to the floor. Two hooks allowed stable placement of a transport cage in front of the exit. The portable transport cage was 36 cm long, 28 cm wide and 33 cm high. Its two entrances were controlled by means of guillotine doors (Figure 1 ).

Cages were installed in racks. Floors of the lower-row cages were 30 cm above ground those of the upper-row cages were 85 cm above ground. Each cage was provided with a PVC pipe or oak branch for perching and one loose oak branch segment for gnawing.
The animals received commercial dry food at approximately 07:30, supplemented with fresh fruits/vegetables at about 15:00. Water was available ad libitum. Room temperature was 20-22°C, with a 12-hr light/dark cycle.
All animals had been trained several months or years prior to this study to voluntarily enter a transport cage. The training was part of the day-to-day animal handling and no extra time was allocated for it. It was reinforced at least once each month during routine management ( e.g., cage sanitization), husbandry ( e.g., weighing) or specific experimental procedures.
The training consisted of the following options:

1. The attending animal caretaker positions a transport cage on the two supporting hooks in front of the cage door. He/she opens the guillotine door of the transport cage and the sliding door of the home cage. Most animals spontaneously react to this by "escaping" into the transport cage (Figure 1 ). The guillotine door is released and the animal is caught. Once in the transport cage, the monkeys usually refuse to a food treat as reward for good cooperation; they do so, however, as soon as they are returned back to their cage.
2. Some animals refuse to leave their home cage. Rather than "escaping" into the transport cage, they escape up to a far corner of the home cage and cling to the mesh ceiling. Such animals are prodded and/ or chased with a stick that is inserted into the cage through the front mesh wall. Usually , the animal quickly accepts the transport cage as a route of escape. The procedure is repeated on different occasions. 3. Juveniles living with an adult already trained companion, usually need, no extra training and follow the example of the adult.
4. Paired animals living in double cages are first confined in one half of the cage with the help of a cage-dividing panel and then caught one at a time.

The cooperation of adult animals during the monthly catching procedure for weighing was evaluated in the present study. The author tested the animals himself. As attending veterinarian, he was well familiar with them.
A monkey was considered to be "cooperative" when it entered the transport cage promptly. The cage was placed on a scale to record the animal's body weight, where after the animal was released back into its homecage and rewarded with an apple. A monkey was considered to be "uncooperative" when it refused to enter the transport cage on its own accord. Such an individual was first encouraged to move. If this was not sufficient to make it go, it was prodded and/or chased with a stick for no longer than 30 seconds caught the animal was weighed and then released back into its cage and rewarded. If a monkey did not respond to the stick within 30 seconds it was chemically immobilised ; and then taken out of its cage for weighing.
Statistical analysis was done with the Chi Sqare test⁷; the level of significance was set at p<0.1.

RESULTS
Of the 341 caged rhesus macaques tested, 87.4% (298/341) were cooperative and entered the transport cage promptly (Table 1 ). Of the animals that were uncooperative, the majority (41/43) entered the transport cage after encouragement (18/43) or after being prodded with the stick (23/43) several times. There were 2 subjects (0.6% of 341 ) that stubbornly refused to enter the transport cage; after being prodded and chased with the stick for 30 seconds they were chemically immobilized and then taken out of their cage.
Neither cage location, sex or housing condition had a noticeable impact on the animals' cooperativeness during the catching procedure. The percentage of upper-row caged monkeys promptly entering the transport cage showed no significant difference with that of lower-row caged monkeys, regardless of the animals' sex and housing condition (Table 1). All together:
lower-row caged animals were cooperative 87.9% (145/165),
upper-row caged animals 86.9% (153/176) of time;
females were cooperative 89.0% (211/237),
males 83.6% (87/104) of time;
single-housed animals were cooperative 85.1% (57/67),
pair-housed animals 88.0% (241/274) of time. Differences were consistently not significant.

DISCUSSION
The present report supports previous findings that macaques, in particular rhesus macaques², can be trained to cooperate rather than resist during the catching procedure^3,5,8. The animals of this study had been trained several months or years ago, and the training was reinforced during routine procedures, requiring temporary or permanent removal of a subject from its cage. The overall success rate was very satisfactory, with 87% of the Research Center's 341 single-housed and isosexually pair-housed adult rhesus macaques instantly entering the transport cage during catching for routine weighing. Thirteen percent of the animals were physically prompted for no longer than 30 seconds to enter the transport cage and 0.6% were chemically immobilized to facilitate their removal from the cage.
It is important to emphasize that the success of any training program depends on the professional skills of the attending animal caretaker(s). Patience, gentleness, firmness and a good understanding of the animals are indispensable qualities of the personnel to ensure the animals' willingness to cooperate. Rhesus macaques are intelligent animals and readily learn simple tasks^9-11. A monkey stubbornly resisting to enter a transport cage is a strong indication that its caretaker(s) are unsuited to do their job.
Contrary to the assumption that pair-housed subjects would be less cooperative during the catching procedure than single-housed individuals, the percentage of pair-housed monkeys voluntarily entering the transport cage was not less than that of single-housed monkeys. This finding was not expected, however, it supports the notion that pair-housing does not affect but rather enhances high standard husbandry and experimental handling of laboratory macaques^12.13.
The transport-cage-training program described in this paper is simple and requires no extra technical equipment such as cage-squeeze-backs. Time investment is minimal and quickly pays off in predictably swift catching of caged subjects that are not unduly distressed when entering the transport cage. The long-term success rate may encourage other institutions and investigators to develop similar transport-cage-catching techniques, based on cooperation of the subjects rather than on mechanical, manual or chemical immobilization. Such techniques will benefit not only the animals - who are exposed to a less disturbing routine handling protocol - but will also increase the methodological validity of research conducted with such animals.

Acknowlegements
Thanks are due to my wife Annie for critically reading this manuscript and providing valuable constructive comments. I am also grateful to Mrs. Jackie Kinney for editing the text. This study was supported by NIH grant RR-OO167 to the Wisconsin Regional Primate Research Center.

References
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