Health StandardsIn general, health standards are defined by the level of known pathogenic organisms present in a research model. All commercial lab mice providers, and virtually all research animal facilities, perform some level of health testing. The level of health testing changes over time as the research community acquires more information about specific organisms.
An example of this changing definition is the recent addition of mouse kidney parvovirus (MKPV) to the list of organisms that are tested for and excluded from some facilities. The addition of MKPV was driven in part by the 2018 publication An Atypical Parvovirus Drives Chronic Tubulointerstitial Nephropathy and Kidney Fibrosis. The realization that MKPV could cause clinical pathologies in research mice led to the decision to monitor, report, and exclude this organism in many lab facilities. We can expect other organisms to be added over the coming years.
When referring to the health status of a lab mouse, a common abbreviation is SPF (Specific Pathogen Free). Some providers, like Taconic Biosciences, have their own health standards such as MPF™, which stands for Murine Pathogen Free™.
An important note about different health designations is how they are defined. Commercial providers often test for 60 to 70 organisms. When acquiring mice, you can request a health report from the sending facility. Commercial providers often make their health reporting data available online.
While there are approximately 1,000 different bacteria in the mouse gut, very few are tested for during routine health screenings. While most of these organisms would be considered commensal and not pathogenic, the presence or absence of specific organisms can have a tremendous effect on research studies.
The emergence of microbiome research over the past decade has led to a better understanding of the impact commensal organisms can have on studies in laboratory mice. While not typically reported by commercial providers, defining the microbiome of mice can help inform the results of a study.
Genetic BackgroundGenetics, if ignored, can wreak havoc on your studies.
To misquote Gertrude Stein, "A mouse is a mouse is a mouse is a mouse". Well...not so much. A mouse is a living organism with an active genome which changes through both spontaneous mutation, active genetic engineering, and possibly during breeding.
While two black mice might look identical to the eye, they could have very different genetic compositions. Even mice with seemingly the same name — such as C57BL/6, C57BL/6N, and C57BL/6J — will have slightly different genetic backgrounds. Without carefully monitoring and maintaining the genetics of your off-the-shelf or genetically engineered model (GEM), it may be difficult or impossible to replicate studies. The influence of genetics on studies is well known; after all, that is why there are thousands of different strains to choose from when planning a study.
There are two aspects of genetics that researchers should be aware of and test for when working with GEMs.
The first is perhaps the most obvious: testing for the gene which has been manipulated, added, deleted, or mutated. This is routinely done by polymerase chain reaction (PCR) testing for the presence or absence of the desired engineered mutation.
The second aspect of genetics to consider is background strain. As noted above, not all black mice or similar strains have the exact same genetic makeup. You will invest many resources into studies using your GEM. Others will be dependent on your studies either through publication or moving a product through the drug development pipeline. Therefore, it makes sense to perform genetic characterization using single nucleotide polymorphism (SNP) testing. SNP testing is inexpensive and fast. When acquiring models from other labs, it is always good practice to perform SNP testing to confirm the exact background strain.
While there is much about genetics that is out of our control and driven by biology, we should take time to understand and monitor the genetics of models we work with.
Environmental FactorsThe environment is defined by the conditions in which your mice are housed. In general, mice are held in standard animal cages with open tops or in IVC racks with filtered covers. They are fed food ad libitum, drink only water which has been filtered, acidified, or chlorinated, and live under a strict twelve-hour light cycle. While these are industry-standard conditions, in practice, they can vary from facility to facility and even within the same institution.
If one of these parameters changes, it can have a dramatic effect on study outcomes. As more studies have been published about the microbiome, we have found that environmental conditions can alter the composition of the microbiome, ultimately leading to unknown downstream effects on your study (Ericsson AC, 2015). If you acquire a model from another lab and find you are not getting the expected results, investigation of the environmental conditions from the originating animal facility may be required.
The same is true even if you are running your experiment in the same facility. If your study produces unexpected results, checking the environmental conditions that the mice were housed in could provide valuable insight. These environmental conditions are often taken for granted but can have a significant effect on the quality of your studies.
TransportationAll mice are transported before conducting a study. That transit may be down a hallway, across the country, or even halfway around the world. All transportation, no matter how good it is, influences study outcomes.
During shipment the ambient light, temperature and humidity will change many times before the mice arrive at your facility. The goal with transportation is to minimize, to the extent possible, its effects on your study. How is this accomplished?
- Utilize a validated shipping container that will keep unwanted organisms out while allowing fresh air to enter and humidity to exit.
- Supply adequate food and water not only for the expected length of the shipment but for an additional day or two in case the shipment gets delayed.
- Account for time. Transportation down the hall from the holding room to the procedure room may require only a few minutes of acclimation. An overnight shipment, or longer, can require up to seven days of acclimation.
Assessing Animal Model QualitySo, are health, genetics, environment, and transportation the only quality considerations? Absolutely not, but controlling for these four factors will support increased consistency and reproducibility across study results. As a scientist, the goal is to obtain valid answers to your questions. Using animal models properly is vital to that achievement.
Consideration of quality parameters discussed here; health, genetics, environment, and transportation will go a long way towards confidence in your results.