Table 1.

Comparison of using colony animals or household pets in an intervention study.

	Colony animals	Pets in homes
Key attributes	Genetically homogenous, particularly for dogs Similar living environment Limited number of pre-study diets (usually) Known health status of animals, usually healthy Possibility of exchange of microbes between individuals	Genetically diverse Wide variety of environments Many different pre-study diets Variety of states of health, known and unknown Different body condition scores, many overweight or obese
Pros	Easy and fast to recruit Excellent compliance with study protocol, sample collection, monitoring Recent veterinary exam (usually) Very low dropout rate Less inter-individual microbiome variability	Lower cost Results are more generalizable to pet population Results may be more replicable in other pets Higher likelihood of ethical acceptability to consumers Can be a tool to increase customer engagement
Cons	Higher cost Results may be less generalizable to pet population Results may be less replicable due to facility and vendor effects	Slower and more expensive to recruit Lower and more variable rates of compliance with study protocol Prolonged, complex protocols or those requiring a veterinarian may not be possible Higher dropout rate (especially cats) More inter-individual microbiome variability

Time, budget, access, research question(s), type of intervention and so on are all factors to consider when recruiting companion animals for a study.