Scientists studied how diet affects the health of Matschie’s tree kangaroos living in zoos. They found that zoo kangaroos eat very different foods than wild kangaroos, which makes them heavier and can cause health problems. By looking at the bacteria in their stomachs, researchers discovered that kangaroos eating more leafy plants had healthier gut bacteria than those eating less natural foods. This research suggests that zoos should feed these animals diets that match what they eat in the wild to keep them healthier.

The Quick Take

  • What they studied: How the food that zoo tree kangaroos eat affects their weight, body health, and the bacteria living in their stomachs
  • Who participated: 31 Matschie’s tree kangaroos living in 16 different zoos across the United States, with stomach bacteria samples collected from 57 samples total
  • Key finding: Kangaroos that were overweight ate significantly more calories, protein, and starchy foods compared to kangaroos at a healthy weight. Kangaroos that ate more leafy plants had different and apparently healthier stomach bacteria than those eating less leafy food.
  • What it means for you: If you work with animals in zoos or care about wildlife conservation, this suggests that feeding captive animals foods similar to their wild diet is important for their health. However, this research only applies to this specific species and would need to be tested further before making major diet changes.

The Research Details

Researchers collected detailed information about what 31 tree kangaroos ate at 16 different zoos over two separate time periods (summer and winter). They recorded exactly how much food each kangaroo ate and what types of food it was. At the same time, zoo staff rated each kangaroo’s body condition (whether it looked overweight, normal, or underweight). The researchers also collected stomach samples from the kangaroos to study the bacteria living inside their digestive systems using a special genetic test called 16S rRNA sequencing, which identifies different types of bacteria without needing to grow them in a lab.

This approach allowed scientists to compare three things: (1) whether heavier kangaroos ate different amounts or types of food than healthier-weight kangaroos, (2) whether the amount of leafy plants in their diet changed their stomach bacteria, and (3) how body weight related to the types of bacteria in their stomachs. By collecting information at two different times of year, they could see if seasonal changes affected the results.

Understanding what captive animals should eat is important because zoo animals often get sick or have trouble reproducing when their diet doesn’t match what they would eat in nature. The bacteria in an animal’s stomach play a huge role in digestion, fighting infections, and overall health. By studying these bacteria, scientists can figure out which diets keep animals healthiest. This research is particularly important for tree kangaroos because previous studies showed that current zoo diets are very different from wild diets, and zoo kangaroos are significantly overweight and have more health problems than wild ones.

This study has several strengths: it included animals from multiple zoos (not just one location), collected information at different times of year, and used modern genetic testing to identify bacteria accurately. However, the sample size of 57 fecal samples is relatively small, and the study only looked at zoos in one country. The researchers relied on zoo staff to rate body condition, which might not be perfectly consistent between different people. The study is observational, meaning it shows relationships between diet and bacteria but cannot prove that diet changes directly cause the bacterial changes.

What the Results Show

Kangaroos that were rated as overweight by zoo staff ate significantly more total calories than kangaroos at ideal body weight. On average, overweight kangaroos consumed about 20-30% more food energy than healthy-weight kangaroos. This extra eating was driven mainly by eating more protein and starchy foods, not more leafy plants.

The most striking finding involved leafy browse (fresh leaves and branches). Kangaroos that were offered large amounts of leafy plants had completely different stomach bacteria compared to kangaroos offered little or no leafy plants. The bacteria in kangaroos eating lots of leaves appeared more diverse and similar to what scientists would expect for animals eating a natural diet.

Interestingly, the amount of leafy browse offered to the kangaroos had a bigger effect on their stomach bacteria than their body weight did. This suggests that what type of food they eat matters more than how much they eat for maintaining healthy gut bacteria.

The study found that seasonal differences (summer versus winter) did not significantly change the results, suggesting that these patterns hold true year-round in zoos. The researchers also noted that the current zoo diets being fed to these kangaroos contain much less fiber and much more starch than what wild tree kangaroos would naturally eat, which aligns with previous research showing that zoo diets are quite different from wild diets.

This research builds on earlier findings showing that zoo tree kangaroos are 30-40% heavier than wild ones and suffer from more infections and reproductive problems. Previous studies suggested that differences in diet might explain these health problems, but no one had actually studied the gut bacteria of these animals before. This study is the first to directly examine the microbiome (the community of bacteria) in tree kangaroos and connect it to their diet. The findings support the theory that diet-related changes in gut bacteria may be responsible for some of the health issues seen in captive tree kangaroos.

The study only looked at zoos in one country and included a relatively small number of animals. The researchers couldn’t study wild tree kangaroos for comparison, so they couldn’t directly compare the bacteria in zoo animals to wild animals. The study shows that diet and bacteria are related, but it cannot prove that changing the diet would actually improve health—that would require a follow-up experiment where some zoos change their diets and researchers track health improvements over time. Additionally, the study relied on zoo staff to rate body condition, which might vary between different people and facilities.

The Bottom Line

Based on this research, zoos should consider reformulating diets for Matschie’s tree kangaroos to include more leafy plants and fiber, and less starch, to better match what these animals eat in the wild. This may help prevent overweight conditions and promote healthier gut bacteria. However, this recommendation is based on one study of a specific species, so any diet changes should be made carefully and monitored by veterinarians. Zoo nutritionists should work with veterinarians to gradually adjust diets while watching for any health changes.

Zoo managers, veterinarians, and nutritionists working with Matschie’s tree kangaroos should pay attention to these findings. Wildlife conservationists interested in captive breeding programs may also find this relevant. The general public who cares about zoo animal welfare should know that diet significantly affects animal health. However, these findings apply specifically to this one species and may not apply to other animals without further research.

Changes in gut bacteria can happen relatively quickly (within weeks to a few months) when diet changes, but improvements in body weight and overall health would likely take longer—probably several months to a year or more. Zoo staff would need to monitor animals carefully during any dietary transitions to ensure they remain healthy.

Want to Apply This Research?

  • If managing zoo animals, track the percentage of leafy browse offered daily and correlate it with monthly body condition scores and any health observations (infections, reproductive success). Create a simple spreadsheet or app entry showing: date, amount of leafy browse offered (as percentage of total diet), body condition score (1-5 scale), and any health notes.
  • For zoo professionals: Gradually increase the proportion of leafy plants in the diet while reducing starchy foods, monitoring body weight and health markers weekly. For the general public interested in animal welfare: Support zoos that prioritize natural diets for their animals and ask about their nutritional programs when visiting.
  • Establish a baseline of current diet composition and body condition scores. After making dietary changes, measure body weight monthly and body condition scores every 2-3 months. Track any changes in health indicators (infection rates, reproductive success, activity levels) over 6-12 months. Consider collecting fecal samples every 3-6 months to monitor changes in gut bacteria diversity as a health indicator.

This research applies specifically to Matschie’s tree kangaroos in zoo settings and should not be generalized to other species without additional research. Any changes to animal diets should only be made under the guidance of qualified veterinarians and animal nutritionists. This study shows associations between diet and gut bacteria but does not prove that diet changes will cure health problems. Zoo professionals should consult with veterinary specialists before implementing dietary changes. This information is for educational purposes and should not replace professional veterinary or nutritional advice.