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 age were used to evaluate the use o f a computerized ultrasound system in estimating changes in body condition. In order to get a wide range of fatness, animals were randomly subjected to four food restriction regimes for 2 weeks. Female rabbits were scanned at six different back sites to estimate perirenal 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, liver and kidneys were recorded. There was a large variation in the weight of the main fat deposits, especially for the perirenal fat (CV = 0·632), indicating its suitability for estimating changes in body condition. Ultrasound measurements of perirenal fat thickness correlated strongly with all carcass fat weight values (r= 0·692 to 0·959;P< 0·001) and the estimated carcass energy content (r= 0·777 to 0·866;P< 0·001) and seem to be more precise predictors than live weight measurements. Multiple regression equations for estimating the main fat deposit weight and estimated carcass energy content using only the live weight as an independent variable hadR2values ranging from 0·47 to 0·59. The accuracy of estimates was improved when ultrasound measurements were used in the regression model (R2values ranging from 0·81 to 0·95). Ultrasound measurement of mean perirenal fat deposit thickness at 3 cm ahead of the 2ndto 3rdlumbar vertebrae was the best predictor for perirenal fat weight (R2= 0·95;P< 0·001), total fat weight (R2= 0·93;P< 0·001) and estimated carcass energy content (R2= 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 approximately 0·895 and 0·967 for total fat weight and estimated carcass energy content, respectively. Results suggest that ultrasound measurements of perirenal fat thickness may be an accurate method for studying changes in body condition of young female rabbits at different times.