How are primates kept and used in animal experiments?

How are monkeys kept?

The keeping conditions in the Swiss Animal Welfare Ordinance stipulate that primates must be kept in groups. In this context, the minimum enclosure dimensions and other provisions are set specifically for each species. Macaques, for example, must be kept in enclosure that are at least 45 m3 in size and are equipped in such a way that the entire three-dimensional space can be used. This is achieved with artificial trees, branches, perching boards, climbing aids, ropes, etc. There must be enough drinking water and food available. Some of this is used as a reward for training, but each animal must have the opportunity to drink enough water and eat enough food during the day.

Primates are very intelligent animals and need interesting occupations, which that must be varied. Pieces of branches that can be gnawed off, toys, cardboard boxes and paper rolls that can be crushed, tubes in which food can be hidden, etc. are tools that are often used. In the field, this is called "enrichment"; the husbandry is made richer and more interesting with objects. Primates also seem to enjoy solving simple cognitive tasks, as they are specifically used in neurological research. The most important enrichment is social enrichment. In other words, animals, which are kept together. Mutual huddling together and grooming are a significant part of this. Anyone who has ever visited the Javanese monkeys in a zoo can easily see what this looks like. When putting a group together, care is taken to ensure that the animals grow up together at an early age and that the group members are compatible with each other. This also contributes to a stable group and to a reduction of stress. Pictures of an experimental primate enclosure in Switzerland can be found here.

What is being done to reduce constraints for primates?

Non-human primates are sensitive animals to whom a social environment is important. They can react nervously to changes in their environment. It is therefore important that the animals live in social groups and that the environment is as stable as possible. Before the animals are considered for an experiment, the researchers train various behaviours, for example, that the animals participate voluntarily in the experiment and solve certain tasks, such as directing their attention to a certain object and grasping it. An important method for this is working with rewards, the so-called "positive reinforcement training". This is often combined with clicker training – analogous to dogs and cats, where animals learn that a reward follows the sound of a "clicker" when they have done a task correctly. A few videos of what this training looks like can be seen here.

A stressed monkey will not work voluntarily in a trial. You cannot force the animal, and if you did, the results would not be reliable. Therefore, it is important for all involved that the animals trust the people and their environment. Every animal has its trusted person, which means that one person is always responsible for the same animals, and the animals always have the same people working with them. This helps primates to feel safe during the experiments and to be able to perform their behavioural tasks calmly. Especially in neurological experiments, a large part of the experiment consists of behavioural tasks in which, for example, banana-flavoured pellets must be picked out of a board with holes. This measures the monkey's dexterity and compares, for example, how well it recovers its fine motor skills after a lesion of the nerves and subsequent therapy. There are some videos about this here.

For measures that help to reduce stress during husbandry, see the following chapter. People working with primates in research must be specially trained. Medical interventions must be carried out to the highest standards, as with humans. The methods used are continuously developed in line with the 3Rs principle.