A comment on a previous post alleged that the scientific enterprise has not taken the 3Rs (Reduction, Replacement and Refinement) seriously, leading to a failure to reduce the number of animals used in research. Subsequent comments from Paul Browne and Luigi provided links to actual data which refute this claim, however it remains an interesting question to explore.
One of the thornier problems in thinking about the justification of using animals is when two or more laudable goals call for opposing solutions. For today's edition of virtual IACUC we will consider what to do when Refinement calls for the use of more animals, in obvious conflict with Reduction.
Although the concept of refining animal research designs can have many aspects, one of the more important parts is the use of techniques which minimize acute stress, distress, etc to the individual subject animal.
There is a very general operating principle which underlies this decision making, namely that within the scope of justified experimental procedures less is better than more. For example, while a single major *surgery (say to implant an intravenous catheter for drug self-administration) might be justified, a second major surgery for a given animal requires extraordinary justification and may very well be refused.
Now, let us suppose that there is a non-zero failure rate for catheters in the course of a typical drug self-administration experiment. Suppose that you have an implanted rat, trained to self-administer cocaine, participating in the study, otherwise healthy when....the catheter fails. Since the animal has not completed the study design it cannot participate in the data analysis. That's bad enough but consider that appropriate groups sizes are necessary to generate the gold standard statistically reliable result- which is essentially a requirement for good interpretation of the outcome, publication, etc. If you can't publish it, it didn't happen. So it may be the case that the loss of one subject blows the entire experiment, potentially obviating the use of all of the other animals on the study.
sourceLet us consider the decisions the investigator and her IACUC might make to ensure that the majority of animals' participation is not wasted.
First, you might just say fine, take your chances with blowing the entire study. A loss of a single subject does not inevitably happen for each group and does not inevitably ruin the analysis. Just re-run the study with a new group when and if the loss of a subject or two because of catheter failure blows the whole thing. Of course, you might just say this is all about probabilities and numbers. How frequently is a study blown, what are the group sizes and how many extra animals are required in the course of a year's worth of experiments? I am uncomfortable with this alternative, however, because by design it dictates that in some cases the full **participation of some subjects will be wasted, simply because another member of the group lost a catheter.
Second, the design may use a excess of animals at the start, relative to what is anticipated to be needed to satisfy the demands of statistical power in the final data analysis. So instead of the 10 that are needed, the investigator always starts with 12 and performs all the surgical and behavioral procedures in all of the animals. The drawback to this approach is, of course, that since a thing like catheter failure cannot be predicted specifically (and if it could, the investigator could probably identify systematic reasons and fix the procedures accordingly) it is likely that there will be a chronic excess of animals in all studies which may or may not be needed. Whether justified or not, animal numbers increase.
Third, it is possible in many cases to surgically repair or replace the catheter on an individual basis as-needed. This, however, requires a second major surgery on an individual which is considered to require a high threshold. This is where we really get down to the difficult call. How important is minimizing the stress to a single animal on experimental need versus systematically lowering the total number of animals required for a given experimental purpose? This is what I would like you to discuss in the comments, DearReader. How would you balance these factors? What decision would you favor if sitting on an IACUC?
How do we balance the permissible procedures in one animal against the need to use additional animals?
*I use this example because it is fairly easy to grasp why less would be better than more, not to be sensational. The niceties of a repeated-measures design versus a between-groups design, statistical power, group size are fascinating but perhaps a bit complicated for a general audience.
**It is not a surface consideration of IACUC decision making but I do think there should be a goal to make each subject's participation in research count as much as possible. With participation in a published data figure as the gold standard of what counts. Yes, there will always be pilot studies and supporting studies that go unreported but I think that we should always strive for the published figure.