Animal Welfare Information Center Newsletter, Spring 1996, Vol. 7 No. 1 *************************

Frequently Asked Questions About Safe Pair-Housing of Macaques

Viktor Reinhardt, D.V.M., Ph.D., Animal Welfare Institute, Washington, D.C.

Permanent pair-housing of previously single-caged macaques has become an accepted way of providing the animals with a more species-appropriate environment in the research laboratory setting. The push towards this change has come primarily from animal care personnel and veterinarians, but there is also an increasing number of scientists who recognize that macaques need social companionship for their behavioral health.

Using a simple pairing technique (1), I have transferred several hundred adult rhesus and stumptailed macaques from single-housing to isosexual pair-housing arrangements at the Wisconsin Regional Primate Research Center. There are several frequently raised questions regarding details of the pair-formation and subsequent pair-housing protocol that I want to address here for the benefit of those who want to make sure that institutionalizing pair-housing of macaques at their facility will not jeopardize the safety of the animals.

1. Why is it necessary that potential partners establish a rank relationship prior to pairing?

The dominance-subordination relationship is a basic condition for the two macaques living together. The animals do not have to engage in possibly injurious fighting but really establish such a relationship during a non-contact familiarization period in a double cage with a grated partition allowing visual, olfactory, and auditory communication. When later being introduced to each other in another cage without a partition, the subordinate partner will respect the dominance of the other, and the two therefore have no reason to fight.

2. How do I know that two animals have established a rank relationship?

Grinning, withdrawing, or turning away when being looked at or when being approached by the neighbor and threatening-against-the-observer-and-glancing-back-at-the-neighbor are indicators of subordination. A relationship is settled if any or all of these behaviors are strictly shown by only one of the two partners; this animal is the subordinate, the other is the dominant one of the dyad. Aggressive behaviors such as threatening or slamming against the cage dividing panel are not suitable to reliably determine the rank relationship between two partners.

3. How long does it take two monkeys to establish a rank relationship?

About 75 percent of the animals show clear signs of a dominance-subordination relationship within the first day of noncontact familiarization (2).

4. Can I pair the animals on the first day of familiarization?

Yes, after you have seen that one partner is subordinate to the other. It is advisable, however, to pair such animals the next morning in order to have a whole day to ascertain their compatibility.

5. Is it really necessary to pair the animals in a different double cage, rather than simply removing the grated partition?

The partners of some, but not all, pairs will engage in vicious territorial antagonism at the moment you remove the cage dividing grated panel, regardless of the fact that they already have a well-established rank relationship. It is impossible to predict which pairs will react in this way since cage neighbors across the aisle may instigate such disputes. With the safety of the animals a priority, it is therefore recommended not to take chances but make it a rule to transfer all potential pairs into a different area where everything is strange to them except the other companion. The management of the pair-housing program can be simplified if a familiarization cage is set aside in a designated test room and potential pairs moved from there to new home cages.

6. What is the cumulative time that I have to invest to form a compatible pair?

About 30 minutes.

7. Is there a way that I can avoid subjecting paired animals to the stress associated with temporary separation during research procedures?

Many procedures--such as venipuncture, topical application of drugs, intramuscular injection, remote sampling via a tether--can be done in pair-housed animals without separating the partners. If two companions have to be physically separated -- for example, during postsurgical recovery, restraint chair experiments, metabolic experiments, food intake studies, urine/fecal collection studies --there is no reason for not allowing them to keep continual visual and auditory contact with each other with the help of a transparent cage divider or a mobile cage. Husbandry-related routine separations --for example, during TB testing, weighing, physical/pregnancy examination--are unlikely to distress the animals because they quickly learn that they are reunited after a short while.

8. Are male pairs less compatible than female pairs?

No, as long as you keep them in male-only areas to avoid sexual competition triggered by the sight of a receptive female.

9. If a pair becomes incompatible, can I pair the animals with other partners?

Yes, the sooner the better.


  1. Reinhardt V. (1988). Preliminary comments on pairing unfamiliar adult male rhesus monkeys for the purpose of environmental enrichment. Laboratory Primate Newsletter 27(4): 1-3.

  2. Reinhardt V. (1994). Pair-housing rather than single-housing for laboratory rhesus macaques. Journal of Medical Primatology 23: 426-431.

This article appeared in the Animal Welfare Information Center Newsletter, Volume 7, Number 1, Spring 1996

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