Use of a body condition score technique to assess health status in a rat model of polycystic kidney disease

Abstract

Simple and noninvasive methods of assessing health and wellbeing are valuable when performing clinical evaluation of rodents used in biomedical research. Body condition score (BCS) techniques have been described for a variety of species, including mice. This method can be a sensitive objective assessment of weight loss in animal models where organ enlargement, ascites, or tumor development may mask weight loss. Although deposition of fat is similar in rats and mice, the mouse BCS technique has not been characterized in rats. Here we used the Han:SPRD rat model for polycystic kidney disease to characterize the effectiveness of the mouse BCS scale when applied to rats. This study showed a positive correlation between BCS score and renal function and a negative correlation between weight and renal function, supporting the use of BCS as an effective, noninvasive method of health assessment in this rat model. Our results also demonstrate that the BCS scale described for mice required a slight modification to capture the delay in fat deposition over the lumbar vertebrae in obese animals.

Figure 1.

To obtain the body condition score, the rat is allowed to rest on the wire top. The vertebrae are assessed by palpation of the lumbar spine. The pelvic bones are assessed by palpation of the hips (illustrated).

Figure 2.

Demonstration of palpation findings for the assessment of rat BCS. This chart was developed as a comparison of previously published evaluation criteria for mouse BCS.^, Fat deposition in the rats was more reliably assessed through the palpation of the fat overlying the dorsal pelvic protuberances instead of that overlying the vertebral column, as is recommended for mice.

Figure 3.

Comparison of carcass weights (CW) and adjusted carcass weights (ACW) of male and female rats. Male carcass weight stays consistent regardless of BCS until the large, polycystic kidneys are removed. Therefore, mild weight gain associated with decline in BCS may assist in the diagnosis of polycystic kidneys. Because the female rats do not develop large renal cysts, the difference between carcass weight and adjusted carcass weight is not reflected in their data.

Figure 4.

As BCS declined, the rats expressed increases in BUN and creatinine, 2 factors used to indicate compromise of renal function. (A) Average BUN levels for male and female rats at each BCS as compared with the published maximum. (B) Average creatinine levels for male and female rats at each BCS as compared with the published maximum.