An animal’s bacteria are shaped by both its genes and its environment, acting as an intermediate factor rather than being controlled by one or the other. According to Gram Research analysis of laboratory animal science, the microbiome creates a unique ‘fingerprint’ reflecting both inherited traits and life experiences, with the animal actively managing its bacterial communities through biological mechanisms despite external influences.
Scientists have discovered that laboratory animals are actually two-in-one systems: the animal itself plus all the tiny bacteria living inside it. According to Gram Research analysis, these bacteria aren’t just passengers—they actively shape how the animal looks, behaves, and responds to experiments. A new review in the Journal of the American Association for Laboratory Animal Science shows that an animal’s bacteria are influenced by both its genes (nature) and its environment like food and light (nurture). This matters because researchers need to understand which bacteria their lab animals have to get reliable results from their experiments.
Key Statistics
A 2026 review in the Journal of the American Association for Laboratory Animal Science found that laboratory animal microbiomes are shaped by both genetic factors and environmental influences like diet and light cycles, creating a unique microbial fingerprint for each animal.
Research shows that animals actively modulate their microbial communities through host-specific biological mechanisms, meaning the microbiome is not left to chance but is actively controlled by the animal’s own body systems.
Microbial communities at different body sites in laboratory animals are shaped by distinct endogenous (internal) and exogenous (external) factors, indicating that the microbiome represents an intermediate influence combining both nature and nurture.
The Quick Take
- What they studied: Whether the bacteria living inside laboratory animals are controlled mainly by the animal’s genes, mainly by its environment, or by a combination of both
- Who participated: This was a review article analyzing existing research about laboratory rodents and their microbial communities—no new experiments were conducted
- Key finding: An animal’s microbiome (its bacterial community) is an intermediate factor, meaning it’s shaped by both the animal’s inherited traits and its environment, acting like a unique fingerprint for each animal
- What it means for you: If you work with laboratory animals or care about research quality, understanding an animal’s bacteria is crucial for getting trustworthy experimental results. Researchers should carefully select animals with the right bacterial profiles for their specific studies
The Research Details
This was a review article, not a new experiment. The researchers examined existing scientific evidence about how bacteria in laboratory animals develop and change. They looked at studies showing how different factors—like what the animals eat, how much light they get, their genetic makeup, and even what bacteria their mothers had—all influence the bacterial communities living in the animals’ bodies.
The researchers focused on understanding whether these bacterial communities are primarily determined by factors the animal can’t control (like its genes), factors from outside the animal (like diet and environment), or a combination of both. They examined bacteria at different locations in the animal’s body, since bacteria in the gut behave differently than bacteria on the skin.
This research matters because laboratory animals are used to test medicines, study diseases, and develop treatments that eventually help humans. If scientists don’t understand what bacteria their lab animals have, they might get confusing or unreliable results. The bacteria can affect how an animal responds to a drug or disease, so controlling and understanding the microbiome is essential for good science.
This is a review article that synthesizes existing research rather than presenting new experimental data. The strength of the conclusions depends on the quality of the studies it reviewed. The article was published in a peer-reviewed journal focused on laboratory animal science, which is appropriate for this topic. However, because it’s a review without new data, readers should look for the original studies cited for specific numbers and details
What the Results Show
The research shows that an animal’s microbiome is not simply inherited or simply determined by environment—it’s both. The bacteria living in an animal’s body reflect a unique combination of the animal’s genetic makeup and its life experiences, creating what researchers call a ‘fingerprint’ of microbial influences.
The evidence indicates that animals actively control and shape their own bacterial communities through biological mechanisms, even though outside factors like food and light also play important roles. Different parts of an animal’s body have different bacterial communities because different body sites have different conditions that favor different bacteria.
This means the microbiome is an ‘intermediate’ factor—it sits between pure genetics and pure environment. An animal’s genes influence which bacteria can survive in its body, but the environment determines which bacteria actually show up. The animal’s body then actively manages these bacteria through immune responses and other biological processes.
The research highlights that maternal effects matter—bacteria passed from mothers to babies influence the baby’s microbiome. Additionally, factors like the animal’s housing conditions, cage mates, and daily routines all contribute to shaping bacterial communities. The review emphasizes that the microbiome is not random or chaotic; instead, it follows predictable patterns based on the animal’s genetics and environment working together.
This review builds on decades of research showing that microbiomes are complex and influenced by multiple factors. Previous studies had debated whether microbiomes were primarily genetic or primarily environmental. This analysis concludes that the answer is ‘both’—the microbiome represents an integrated system where nature and nurture interact continuously. This perspective aligns with the modern understanding of ‘holobionts,’ which treats the animal and its bacteria as a single biological unit rather than separate entities.
As a review article, this study doesn’t present new experimental data, so its conclusions depend on the quality of previously published research. The review focuses on laboratory rodents, so findings may not apply equally to other animals. The article doesn’t provide specific percentages or numbers showing how much genetics versus environment influences the microbiome—it establishes that both matter without quantifying their relative importance. Readers should consult the original studies cited for specific experimental details and measurements
The Bottom Line
For researchers: When designing experiments with laboratory animals, carefully consider and document the microbiome status of your animals, as it can influence experimental outcomes. Select animals with appropriate microbial profiles for your specific research question. For animal care facilities: Maintain consistent environmental conditions and document them, as these shape the microbiome. For those interpreting research: When reading studies using laboratory animals, consider whether the microbiome was controlled or measured, as it may affect result reliability. Confidence level: High—this reflects strong consensus in the scientific community
Laboratory researchers and animal facility managers should prioritize this information. Pharmaceutical companies testing new drugs should understand how microbiomes affect their results. Scientists studying disease should recognize that animal microbiomes influence disease development. People reading about animal research should understand that microbiome differences between studies might explain different results. This is less directly relevant to the general public unless they work in research or care about research quality
Changes to an animal’s microbiome can occur relatively quickly—within days to weeks—when environmental conditions change. However, establishing a stable, predictable microbiome in a research setting typically takes several weeks. Researchers should allow adequate time for microbiome stabilization before beginning experiments
Frequently Asked Questions
Do lab animals’ bacteria come from their genes or their environment?
Both. Research shows that an animal’s bacteria are shaped by inherited genetic traits and environmental factors like food and housing. The animal’s body actively manages these bacteria, creating a unique microbial fingerprint combining nature and nurture influences.
Why does it matter what bacteria are in laboratory animals?
The bacteria in lab animals influence how they respond to diseases and medicines. If researchers don’t understand or control the microbiome, their experimental results may be unreliable or hard to repeat, affecting the quality of medical research.
Can changing an animal’s environment change its bacteria?
Yes. Changes to diet, light cycles, housing conditions, and cage mates can shift an animal’s bacterial communities within days to weeks. However, the animal’s genes also influence which bacteria can survive, so environment alone doesn’t determine the microbiome.
How do scientists know what bacteria their lab animals have?
Scientists can test samples from the animal’s gut or other body sites to identify bacteria present. They should also document the animal’s genetics, age, diet, housing conditions, and maternal background, as all these factors influence the microbiome.
Want to Apply This Research?
- If managing laboratory animals, track and log environmental conditions (diet type, light/dark cycle duration, housing density, cage changes) weekly, then correlate these with any changes in animal behavior or experimental outcomes to identify microbiome-related patterns
- For researchers: Implement a microbiome documentation protocol where you record the source, age, housing conditions, and diet of all laboratory animals used in experiments, creating a baseline understanding of each animal’s likely microbial profile
- Establish a long-term tracking system that monitors environmental consistency in animal facilities and documents any changes to housing, diet, or care routines. Periodically review whether experimental variability correlates with changes in these environmental factors, which influence the microbiome
This article summarizes scientific research about laboratory animal microbiomes and is intended for educational purposes. It does not provide medical advice for humans or animals. If you work with laboratory animals, consult your institution’s animal care guidelines and veterinary staff. If you have health concerns, consult a qualified healthcare provider. Research findings in animal models do not always translate directly to humans. The conclusions presented reflect current scientific understanding but may be updated as new research emerges.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.