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. 2025 May 20;41(1):15.
doi: 10.1186/s42826-025-00246-6.

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

Annemiek Maaskant  1   2 , Niels R Blees  3 , Antoine Smits  4 , Ronald J Corbee  3 , Jaco Bakker  4 , Jan A M Langermans #  4   5 , Edmond J Remarque #  4
Affiliations

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

Annemiek Maaskant et al. Lab Anim Res. .

Abstract

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.

Keywords: Defecation frequency; Fiber; Lactose; Monkeys; Nutrition; SFCAs; Stool consistency; Waltham Faeces Score; Welfare.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: All animals were housed following Dutch law and international ethical and scientific standards and guidelines (EU Directive 63/2010). All procedures and husbandry were compliant with the above standards and legislations. No interventions other than those required for veterinary care were performed on these animals. Therefore, following the law on animal experiments and the EU directive, no approval from the competent authorities was required. Nevertheless, additional approval was obtained from the institutional animal welfare body (IvD 018A). The BPRC is accredited by the Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC) International. Consent for publication: Not applicable. Competing interests: Kasper Faunafood (Woerden, The Netherlands) and Altromin Spezialfutter GmBH (Lage, Germany) kindly sponsored the diets used in this study. The sponsors had no role in the study design; in the sample collection, analyses or data interpretation; in the writing of the manuscript, nor in the decision to publish the results.

Figures

Fig. 1
Fig. 1
Mixed model results showing estimated mean fecal consistency scores, and whiskers indicate a 95% confidence interval for each diet, for all animals (red, left) and for the diarrhea (green, middle) and control group (blue, right) separately. In the diarrhea group, both LFLF and LFHF showed a decrease in fecal score, in the control group LFHF showed a decrease in mean score
Fig. 2
Fig. 2
Mixed model results showing estimated mean defecation frequencies. The Whiskers indicate a 95% confidence interval for each diet, for all animals (red, left) and for the diarrhea (green, middle) and control group (blue, right) separately. LFHF showed an increase in defecation frequencies, compared to an overall decrease for LCMF-hy
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