Falciform fat:femur length ratio provides a novel method for objective postmortem estimation of total body fat in overweight and obese cats

Abstract

Determination of the nutritional condition, including estimation of amounts of total body fat (tBF), at routine postmortem examination of cats is typically based on subjective visual assessment. Subjective assessment may result in uncertainties regarding degree of overweight, and objective methods that provide a numerical value reflecting the tBF could be valuable to accurately judge excess body fat. We investigated if the falciform fat pad weight (FFPW) was correlated to tBF and could be used to detect overweight and obesity in cats. The FFPW and the femur length (FL) were recorded at postmortem examination in 54 cats and the FFPW:FL ratio (FFR) calculated. Each cat was additionally assigned to a fat category (FC) according to subjective assessment. Computed tomography was used to determine tBF as the body fat percentage (%BF), the body fat volume (BFV), and BFV normalized to animal size (nBFV) in 39 cats. There was strong correlation between the FFPW and the BFV (r = 0.888) and between the FFR and the nBFV (r = 0.897). The correlation between the nBFV and %BF was very strong (r = 0.974). Using a lower FFR cutoff value of 3.5 for obesity and 1.6 for overweight, there was a discrepancy in FC between using the FFR and subjective assessment in 6 of 54 cats (11%). We conclude that the FFPW increases proportionally with tBF and that the FFR provides a method for objective tBF estimation. We suggest introducing the FFR to feline postmortem examination protocols as an objective estimate of tBF.

Keywords: adipose tissue; cats; multidetector computed tomography; obesity; pathology.

Figures 1, 2.

The opened abdominal cavity of a cat, and measuring a cat femur. Figure 1. Macroscopic appearance of the ventral aspect of the abdominal cavity of a cat. After incision of the linea alba, the falciform fat pad (F) has been separated from the abdominal wall by blunt dissection. To exteriorize the falciform fat pad, its attachment to the ventral abdominal wall at the xiphoid process (arrow) is transected. OM = greater omentum; S = spleen. Figure 2. Measurement of cat femur length using calipers. The greatest distance between the proximal aspect of the greater trochanter and the distal articular surface of the lateral femoral condyle is measured.

Figures 3, 4.

Correlations of body fat percentage and falciform fat pad weight:femur length to normalized body fat volume. Figure 3. There was very strong correlation between the body fat percentage (%BF) and normalized body fat volume (nBFV; n = 39 cats; p < 0.001, r = 0.931, r² = 0.867, regression equation %BF = 14.396 + [3.199 × nBFV]). When cats with muscle atrophy (n = 15, open circles) and hypertrophy (n = 1, gray-filled circle) were excluded, the correlation was even stronger (p < 0.001, r = 0.974, r² = 0.949, regression equation %BF = 10.697 + [3.655 × nBFV]). Figure 4. There was very strong correlation between the falciform fat pad weight:femur length ratio (FFR) and nBFV (p < 0.001, r = 0.897, r² = 0.805, regression equation ln(FFR) = −1.459 + [1.356 × ln(nBFV)]). Values were transformed to the natural logarithm given the failed normality test. Solid line in graph is the regression line.

Figures 5–7.

Boxplot graphs of normalized body fat volume (nBFV), body fat percentage (%BF), and falciform fat pad weight:femur length ratio (FFR) to fat categories in underweight (n = 3), normal weight (n = 8), overweight (n = 17), and obese (n = 11) cats. Figure 5. Boxplot graph of nBFV in the 4 fat categories. The nBFV was higher in obese compared to overweight and normal weight cats (p = 0.007 [**] and p < 0.001 [***], respectively) and in overweight compared to normal weight cats (p = 0.021 [*]). Figure 6. Boxplot graph of %BF in the 4 fat categories. The %BF was higher in obese compared to overweight and normal weight cats (p = 0.016 [*] and p < 0.001 [***], respectively) and in overweight compared to normal weight cats (p = 0.027 [*]). Figure 7. Boxplot graph of FFR in the 4 fat categories. The FFR was higher in obese compared to overweight and normal weight cats (p = 0.003 [**] and p < 0.001 [***], respectively) and in overweight compared to normal weight cats (p = 0.028 [*]).