A Comprehensive Analysis of Use of Small Laboratory Animals in Preclinical Research: A Five-Year Quantitative Descriptive Analysis

Background: Animal models play a critical role in biomedical research, yet comprehensive data on the types and distribution of animals used in different research contexts are sparse. Objectives: This study aims to provide a detailed analysis of small laboratory animals used in preclinical research, highlighting the types of animal species used, study types, and disease systems targeted. Materials and Methods: A total of 841 freely available full-text original research articles indexed in the PubMed database from January 2016 to January 2021 were analyzed. Variables recorded included a) type of animal species used for research, b) type of animal studies (in vivo, in vitro, mixed, transgenic, xenograft, others), c) distribution of animals across different study types, d) system and disease-wise distribution of studies, and e) type of animal used and type of studies conducted for different systems/diseases Results: Mice were used in 75.98% of studies, followed by rats at 22.12%. Most studies were in vivo (35.43%), followed by mixed studies combining both in vivo and in vitro methods (24.49%). The gastrointestinal and genitourinary systems (GIT/GU: 21.04%) and the central nervous system (CNS: 15.33%) were the most studied. GIT/GU research focused on diseases like nonalcoholic steatohepatitis, colitis, inflammatory bowel disease, and various carcinomas. For CNS, studies predominantly addressed Parkinson’s disease, Alzheimer’s disease, and multiple sclerosis. In GIT/GU studies, mice were the most commonly used species (140/177), with in vivo (55/177), mixed (43/177), and xenograft (36/177) approaches. For CNS diseases, in vivo approaches (72/129) were prevalent, utilizing both mice (39/129) and rats (32/129). Conclusion: The distribution of animal species in these studies validates that mice, followed by rats, are still very commonly used small animals for preclinical research. In disease areas like GIT/GU and CNS, there is a notable use of mixed and transgenic models, which offer a comprehensive understanding of disease mechanisms. The preference for mixed and transgenic mouse models in cancer research, particularly xenografts, underscores the shift towards more sophisticated and disease-relevant animal models.