Abstract

Gastroenterocolitis is a leading cause of morbidity and mortality in Douc langurs (Pygathrix nemaeus) at the San Diego Zoo. A review of necropsy information revealed that gastroenterocolitis was present in 11/52 (21%) animals and was the primary finding in 8/52 (15%) necropsies.⁴ This abstract discusses the use of gastric sample analysis in colobine primates as an assessment of gastrointestinal function and subsequent health.

The Douc langurs at the San Diego Zoo have had intermittent problems with gastrointestinal disease. Symptoms range from mild to severe diarrhea and vomiting with subsequent metabolic derangement. There is little published information on the gastric physiology of colobine primates. To better characterize the gastric environment, analyses of gastric contents have been performed over the past 3 years. Because of similarities between ruminants and folivorous forestomach fermenters, the rationale was to utilize the same tests used to evaluate rumen fluid. Gastric samples from Douc langurs, Francois langurs (Trachypithecus francoisi), Kikuyu colobus (Colobus guereza) and Angolan colobus (Colobus angolensis) were examined. Gastric samples were obtained using a large bore (18–28 French) red-rubber tube (Sovereign Feeding Tube and Urethral Catheter, Sherwood Medical, St. Louis, MO, USA or Robinson Catheter, Davol Inc., Cranston, RI, USA) and either a catheter tip syringe or a specimen trap (Sherwood Medical, St Louis, MO, USA) attached to a suction unit. Minimal sample volumes of 10–20 ml were sought.

Testing of each sample included pH measurement, occult blood detection, methylene blue reductase activity assessment, wet-mount examination for protozoans, and cytology to assess the bacterial flora and screen for evidence of inflammation. The pH was measured using pH strips (J.T. Baker Inc., Phillipsburg, NJ, USA). Occult blood was measured using Hematest Reagent Tablets (Miles Inc., Diagnostics Division, Elkhart, IN, USA). Methylene blue reductase activity quantification is a means of assessing anaerobic bacterial fermentation and is used in ruminants to assess rumen microflora health. The redox potential of the bacterial population of the rumen allows for reduction of methylene blue.^2,3,5 A 10 ml aliquot of gastric contents was mixed with 0.5 ml of a 0.03% methylene blue solution and the time for the solution to clear recorded. A healthy population of rumen flora is able to reduce methylene blue within 6 minutes.⁵

Table 1 summarizes sample distribution for species, number of individuals, number of samples, and health status. A clinically normal animal is defined as one that was examined for a routine procedure or follow-up on a resolved problem and was not showing clinical signs of illness at the time of the examination. A clinically abnormal animal was defined as one examined for any other reason. The results for pH testing are shown in Table 2. The normal pH range of langur gastric contents has been reported as 5.0–6.7.¹ The pH for the samples presented here was generally higher. This may be due to differences in methodology and sampling location. Contamination of a sample with saliva can artificially elevate the pH.³ There was little difference in the average pH between clinically normal and abnormal animals. However, the range of pH values was greater for the clinically abnormal group. Most samples were occult blood negative. Positive results can be attributed to gastric hemorrhage, iatrogenic trauma during sample collection, post-surgery, or a false-positive result secondary to reactive non-heme compounds found in gastric contents. The times to reduce methylene blue in clinically normal and abnormal animals is shown in Table 2. Eighty-four percent of clinically normal animals had methylene blue reductase times of 6 minutes or less whereas only 35% of abnormal animals reduced methylene blue in 6 minutes or less. Sixty-five percent of clinically abnormal animals compared to 15.8% of clinically normal animals had methylene blue reductase times greater than 6 minutes. A gastric sample with pH less than 6 and/or a methylene blue reductase greater than 6 minutes should be considered abnormal and the animal scrutinized for diseases affecting the gastrointestinal system.

Table 1. Summary of samples based on species, individuals, number of samples, and health status

*The number of samples differs for each test because not all tests were performed on all samples.

Table 2. Gastric content pH values for clinically normal versus abnormal animals

*The number of samples differs for each test because not all tests were performed on all samples.

Table 3. Gastric content occult blood results for clinically normal versus abnormal animals

*The number of samples differs for each test because not all tests were performed on all samples.

Table 4. Gastric sample methylene blue reductase times for clinically normal versus abnormal animals

*The number of samples differs for each test because not all tests were performed on all samples.

The gross appearance of the gastric samples was not objectively evaluated. Subjectively, a gastric sample that was watery, brown, had a fetid odor, or contained large heterogeneous particulate matter was considered abnormal. Normal samples were green and viscous with a homogenous consistency. The wet mount and cytologic data need further analysis but were useful in detecting gastric parasitism (Trichuris sp.) in two Kikuyu colobus.

Tests used for rumen sample analyses are applicable to other foregut fermenters. Gastric content analyses can be used as an additional diagnostic tool for assessing the health of colobine primates. Abnormal results may be indicative of primary gastrointestinal abnormalities or secondary to other diseases. Additional studies evaluating the gastric physiology of colobines, including volatile fatty acid content of gastric contents, is warranted.

Acknowledgments

The authors wish to thank the Clinical Pathology Laboratory at the Zoological Society of San Diego for their diagnostic support.

Literature Cited

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2.  Dirksen G. Ist die metylenblauprobe als schneltest fur die klinische pansensaftuntersuchung geeignet? Dtsch Tierarztl Wochenschr. 1969;76:305–309.

3.  Garry FB. Indigestion in ruminants. In: Smith B, ed. Large Animal Internal Medicine. St. Louis, MO: The C.V. Mosby Co; 1990:772–775.

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5.  Rings DM, Rings BR. Rumen fluid analysis. Agri-Practice. 1993;14:26–29.