How do you determine obesity in a rat? - briefly
Obesity in laboratory rats is assessed by calculating a body mass index that relates body weight to naso‑anal length, with values above strain‑specific cut‑offs indicating excess adiposity. Confirmation can be obtained through body‑composition methods such as dual‑energy X‑ray absorptiometry or magnetic resonance imaging, which quantify fat mass directly.
How do you determine obesity in a rat? - in detail
Assessing adiposity in laboratory rodents requires quantitative and qualitative measurements that together define an obese phenotype.
Body weight alone is insufficient because growth and strain differences influence absolute mass. A composite index that incorporates length provides a more reliable indicator. The Lee index, calculated as the cube root of body weight (g) divided by naso‑anal length (cm) and multiplied by 100, yields a value >0.300 for rats classified as obese.
Body composition analysis offers direct quantification of fat mass. Techniques include:
- Dual‑energy X‑ray absorptiometry (DEXA): delivers whole‑body percentages of lean tissue, fat, and bone mineral density with minimal radiation exposure.
- Magnetic resonance imaging (MRI) and computed tomography (CT): produce high‑resolution images for regional fat distribution, distinguishing visceral from subcutaneous depots.
- Nuclear magnetic resonance (NMR) spectroscopy: provides rapid, non‑invasive whole‑body fat content measurement.
Post‑mortem dissection remains a gold standard for depot-specific analysis. Epididymal, retroperitoneal, mesenteric, and perirenal fat pads are excised, weighed, and expressed as a percentage of total body weight.
Biochemical markers complement anatomical assessments. Elevated plasma leptin, insulin, and triglyceride concentrations correlate with increased adiposity. Glucose tolerance tests and insulin tolerance tests reveal metabolic disturbances associated with excess fat.
Standardized housing, diet, and age controls are essential to reduce variability. Applying multiple complementary methods—anthropometric indices, imaging, tissue weighing, and metabolic profiling—ensures accurate identification of obesity in rat models.