Implications for health assessments of the relationship between body fat percent and body condition scoring in Fisher 344 x brown Norway rats varying by sex and age (2026)

Logan, C. N., Ramirez, M., Smith, S. et al.

Abstract

Body condition scoring (BCS) has been implemented across farming, veterinary, and research settings1–3 to probe body fat reserves for quick and effective assessment of animal welfare. Some strains of rats, including the male Fischer344 x Brown Norway F1 hybrid (FBN) rat, which is available aged from the NIA colony, experience excess weight gain after middle age. This weight gain leads to an obese BCS,7 and thus, these rats must be food restricted until they reach a healthy BCS. the currently employed BCS scale and associated body composition have not been assessed and validated for aged male and female rodents nor have they been evaluated in relation to a calorically restricted diet. To evaluate the current BCS guidelines’ validity for accurately rating young and aged male as well as young and aged female rats, we collaborated with 2 veterinarians experienced in laboratory animal medicine employed by the University of Florida, who have several years of training and experience completing BCS analysis of rats. Following the assignment of the BCS scores by the veterinarians, we scanned the rats in a TD NMR body scanner to quantify the total percentage of fat, lean mass, and water amounts. Thus, here we compared assigned BCS values to body fat and lean mass amounts in young and aged, male and female rats. This provides information on the validity and reliability of current BCS assessment protocols.