Rhesus macaques (Macaca mulatta) are widely used in behavioural neuroscience because of the perceptual, cognitive and neuroanatomical similarities that they share with humans.  To motivate them to perform in cognitive tasks, researchers sometimes apply fluid control protocols, which limit an individual’s access to freely available water but allow additional fluid intake to be “earned” through the performance of correct task responses. One primary concern with using this technique is that the macaques could become dehydrated or experience poor welfare. Despite the widespread use of fluid control, and the welfare concerns surrounding it, there has been no systematic study to measure its effects. This study assesses the behaviour and physiology of rhesus macaques undergoing fluid control protocols in order to determine whether such methods result in poor welfare.

Following a period of free access to water, four male rhesus macaques received four-week blocks of a 5-day fluid control protocol (5 days of fluid control followed by 2 days of free water access at the weekend) and a 7-day fluid control protocol (fluid control on every day of the week).  Each protocol was run twice, in either an ABAB or BABA order, balanced across animals.  The macaques were videoed in their home cages for one hour at six different time points every week.  Their behaviour was scored blind for a range of variables relating to welfare, including social activity, stereotypy and locomotion.  Physiological measures of hydration state were also taken at the end of each block. These were concentrations of sodium, potassium, calcium haematocrit and urea in the blood, and urine osmolality, creatinine and specific gravity.

We report on how changes in fluid control protocols affect physiology and behaviour of macaques, and discuss the implications of our findings in relation to their welfare.