Many diet formulas can be used as treats for enrichment and reward.
See all of these pages for detailed information:
Tablets / "Precision Pellets" (all species)
Small Animal Enrichment Program - Mice, Rats, Hamsters, Rabbits, Ferrets, Guinea Pigs
LabTreat Enrichment Tablets for Primates
Vitamin Supplement Tablets for Non-Human Primates
References
An excellent database of articles about laboratory animal enrichment is maintained by Viktor and Annie Reinhardt of the Animal Welfare Institute in Washington, DC.
It’s available in three parts:
1. Refinement and Environmental Enrichment for All Animals kept in Laboratories