Evaluation of commercial diets on fecal consistency and defecation frequency in rhesus macaques (Macaca mulatta) with chronic intermittent idiopathic diarrhea.

Background: Recurrent diarrhea is common health and welfare problem in captive rhesus macaques (Macaca mulatta). Aside from infectious causes, dietary factors have been implicated in diarrhea. Therefore, the main objective of this study was to evaluate commercially available pelleted diets in rhesus macaques with chronic intermittent idiopathic diarrhea. The main differences between these diets were lactose and fiber content. A randomized cross-over diet study was conducted to investigate the influence of each diet on fecal consistency and defecation frequency as indicators of diarrhea. Nine animals with chronic intermittent diarrhea and four controls were included. Each diet was fed for approximately three months, with a similar wash-out period after each diet cycle. The fecal consistency was graded using the Waltham Faeces Scoring system, with a cutoff score of > 3.5 indicating diarrhea. Both groups and diets were compared by both mixed and fixed effect models.

Results: Descriptive data showed that the mean fecal consistency score was highest in the diarrhea group in the standard diet at 3.71 ± 0.456 whereas the lowest mean fecal consistency scores were observed for lactose-free and high fiber diet in both diarrhea (3.25 ± 0.423) and control group (3.04 ± 0.346). A significant improvement of the fecal consistency score was detected in the diarrhea group when fed lactose-free diets (-0.41(-0.65 - -0.16, P < 0.01) and -0.47(-0.68 --0.25, P < 0.0002), respectively). Lactose-free and high fiber content showed the best outcome regarding improvement of the fecal consistency score -0.47(CL -0.68-- 0.25, P < 0.0002). Defecation frequency increased in both groups with 1.21(CL 0.65 - 1.78, P < 0.00001) per observation day when fed a lactose-free, high-fiber diet.

Conclusions: Lactose-free and high-fiber showed overall the best improvement of the fecal consistency in animals with diarrhea. Switching to commercially available lactose-free diets may decrease diarrhea incidence in rhesus macaques suffering from chronic intermittent idiopathic diarrhea. Nevertheless, additional nutritional research is warranted and establishing optimal nutritional requirements for captive macaques will add to our ability to understand and improve dietary interventions.