Ewe whole body composition predicted in vivo by real-time ultrasonography and image analysis

• Body composition of two breeds of mature ewes was predicted using real time ultrasonography measurements in the live animal.
• Simple and multiple regression equations incorporating fat and muscle measurements and live weight were used as predictors.
• Absolute values of body composition were estimated with higher accuracy than their proportions.
• Real-time ultrasonography provided a good estimate of body fat content

The relationship between ultrasound measurements and the empty body chemical composition of mature ewes was studied in two breeds. The breeds were a milk-producing breed Churra da Terra Quente—CTQ (n = 33; live weight 42.0 ± 7.3 kg, mean ± SD), and a meat breed Ile de France—IF (n = 23; live weight 60.7 ± 9.1 kg, mean ± SD). Fat and muscle depths were measured in the live animals by real-time ultrasound scanning (RTU; 7.5 MHz probe) over the 13th thoracic, and between the 3rd and 4th lumbar vertebrae, and total tissue depth over the 11th rib. Following slaughter, the carcass and non-carcass components of the empty body were combined and subjected to chemical analysis and assessment of energy value. Data obtained by RTU after image analysis was used to develop simple and multiple regression models for each breed. The traits most accurately estimated from single RTU measurements were the absolute values for fat content and energy value of the empty body. The respective coefficients of determination (R2) for IF and CTQ ewes using subcutaneous fat depth over the 13th thoracic vertebra were 0.768 and 0.908 for fat, 0.821 and 0.900 for energy; and for measurements between the 3rd and 4th lumbar vertebrae were 0.845 and 0.911 for fat, 0.852 and 0.906 for energy. All these coefficients were significant (P < 0.01). The best prediction models included one to three RTU measurements and were better for CTQ ewes, where adjusted R2 values ranged from 0.923 (P < 0.001) for water to 0.969 (P < 0.001) for protein, than for IF ewes, where the range was 0.394 (P < 0.01) for protein to 0.940 (P < 0.001) for fat. The results revealed good estimates of the fat and energy content of the empty body of both breeds and also good estimates of protein content for CTQ ewes, but poor estimates of protein content for IF ewes, with the best prediction models for each body component being different from each breed. Consequently, it is concluded that predictive models that are specific to the breed and circumstances of the study in which they are to be used will have to be established to have a practical application.