Influence of Multiple Factors on Rhesus Macaque (Macaca mulatta) Use of a Feeding Enrichment Device.

We studied the effect of different filler items on rhesus macaques' use of a feeding enrichment device called the 'browsing bowl.' We examined use of the device as affected by calories, sugar content, and volume of different fillers as well as the presentation of each filler as 1) whole, loose, or smeared and 2) frozen or not frozen. In addition, we examined the impact of age and sex of the monkeys on use of the device. Fifty-eight macaques were observed across 30-min sessions with the device, with one session for each of 12 different fillers. Scans occurred every 2.5 min, at which point the monkeys were scored as interacting or not interacting with the device. Subjects were recorded as interacting with the device during 47.6% of all observed scans and during 80% of the first 2 scans per session. Frozen items were associated with a significantly higher mean engagement (ME; proportion of observed scans in which animals engaged with the device) than items that were not frozen items (t(57) = 12.91, P < 0.001). Whole presentations were associated with a significantly higher ME than for smeared (P < 0.001) or loose (P = 0.005) items. Loose items were associated with a significantly higher ME (P < 0.001) than for smeared items. Sugar and calorie content did not impact use of the device. Younger monkeys used the device more than for older monkeys, and female monkeys used the device more than did males. We conclude that some filler items encourage more foraging behavior than others, and that it is possible to generate relatively long (up to 30 min) foraging bouts by altering the presentation of foods rather than increasing calories or sugar content. Indeed, some fillers were still present and engaged with at the end of the observation session.