Use of real-time ultrasound measurements of fat thickness and longissimus thoracis muscle characteristics for predicting body fat depots in crossbred hair ewes

This study aimed to predict body fat depots using ultrasound measurements (USM) of fat thickness and longissimus thoracis muscle characteristics in crossbred hair ewes. A total of 24 animals with a mean body weight (BW) of 37 ± 4 kg and a body condition score of 2.39 ± 0.49 were used. USM was recorded 24 h before slaughter and included: subcutaneous fat thickness (SFT), area (LTMA), amplitude (LTA), and depth (LTD) of the l. thoracis muscle and kidney fat thickness (µKFT). After slaughter, the internal fat (IF) was separated, classified, and weighed as mesenteric (MF), omental (OF), or pelvic fat (PF). The left half was then separated into subcutaneous and intermuscular fat (CF), and the muscle and bone tissues were weighed separately and adjusted to take account of the whole animal. Total body fat (TBF) was determined to be the IF plus the CF weights. LTA and LTMA correlated poorly to moderately with fat depots (0.37 ≤ r ≤ 0.74, P < 0.05). Other than CF, µKFT showed poor to moderate correlation with the other depots of body fat (0.44 ≤ r ≤ 0.75, P < 0.05). The regression model used to predict MF had r² of 0.87 (RSD=0.14 kg) and included BW and LTMA (P<0,05). OF and PF were predicted with r² of 0.55 and 0.44, respectively, including µKFT (RSD = 0.20 and 0.17 kg). IF was predicted by empty BW, LTMA, and µKFT with r² as 0.81 (RSD=0.30 kg). For TBF, EBW and LTMA explained 72 % of its variation (RSD= 0.59 kg). USM of fat thickness and l. thoracis muscle characteristics can improve the accuracy of predicting body energy reserves in crossbred hair ewes.