The use of ultrasound measurement of perirenal fat thickness to estimate changes in body condition of young female rabbits

Forty-two New-Zealand x Californian young female rabbits of 4-5 months of a ge were used to evaluate the use of a computerized ultrasound system in est imating changes in body condition. In order to get a wide range of fatness, animals were randomly subjected to four food restriction regimes for 2 wee ks. Female rabbits were scanned at six different back sites to estimate per irenal fat thickness, using a real-time ultrasound unit equipped with a 5.0 -MHz sector probe. After scanning, all animals were weighed and slaughtered . The weights of hot carcass, cold carcass, perirenal fat, scapular fat, li ver and kidneys were recorded. There tons a large variation in the weight o f the main fat deposits, especially for the perirenal fat (CV = 0.632), ind icating its suitability for estimating changes in body condition. Ultrasoun d measurements of perirenal fat thickness correlated strongly with all carc ass fat weight values (r = 0.692 to 0.959; P < 0.001) and the estimated car cass energy content (r = 0.777 to 0.886; P < 0.001) and seem to be more pre cise predictors than live weight measurements. Multiple regression equation s for estimating the main fat deposit weight and estimated carcass energy c ontent using only the live weight as an independent variable had R-2 values ranging from 0.47 to 0.59. The accuracy of estimates was improved when ult rasound measurements were used ill the regression model (R-2 values ranging from 0.81 to 0.95). Ultrasound measurement of mean perirenal fat deposit t hickness at 3 cm ahead of the 2(nd) to 3(rd) lumbar vertebrae was the best predictor for perirenal fat weight (R-2 = 0.95; P < 0.001), total fat weigh t (R-2 = 0.93; P < 0.001) and estimated carcass energy content (R-2 = 0.90; P < 0.001). A validation group of 11 rabbit does was used to validate the ultrasound regression equations, showing that their mean accuracy was appro ximately 0.895 and 0.967 for total fat weight and estimated carcass energy content, respectively. Results suggest that ultrasound measurements of peri renal fat thickness may be an accurate method for studying changes in body condition of young female rabbits at different times.