Ultrasonic nondestructive examination of intramuscular fat using ultrasonic for live Congjiang pig

Abstract: As one of the most important evaluating indicators of pork quality traits, the intramuscular fat (IMF) content has an influence on tenderness, flavor and succulence of the meat. Excessive and long-term selective breeding of high lean percentage and fast growth rate has resulted in generally lower IMF content in pigs. For traditional detection method, samples used for determination of IMF content usually come from slaughtering, which is difficult to operate and costs high. Congjiang pigs belongs to the characteristic local small breeds in China, and is well known for its small-sized body, slow growth, early sexual maturity, and low genetic diversity. The IMF percentage of Congjiang pigs reaches the domestic breeds standard level, but the population variation of IMF content is rather larger, with variation coefficient of 31.71%, suggesting efforts should be made to strengthen the breeding and improve group uniformity. The aim of the study was to predict the IMF percentage in longissimus muscle of live Congjiang pig using real-time ultrasound image. In this research, the body weight (BW), backfat thickness (BFT), loin muscle deepness (LMD) and two longitudinal real-time ultrasound images were collected across the 10th to 11th rib and 5 cm off-midline on live pigs from 110 Congjiang pigs. 31 candidate image parameters of gray gradient and 4 direction (0, 45, 90, 135 angle) graylevel cooccurrence matrix within a defined region (50*50 pixel region) located at the center of longissimus muscle across the 10th to 11th rib for each ultrasound image were obtained using image analysis software (Matlab R2015b). After slaughter, a slice of longissimus muscle from left carcass across the 10th to 11th rib was cut off immediately for determining the IMF percentage by the petroleum ether extraction method. Each test was repeated three times, the mean value as the final IMF content. The model to predict longissimus muscle IMF percentage was developed using multivariate linear regression analysis with carcass longissimus muscle IMF percentage as dependent variables and BW, BFT, LMD and image parameters as independent variables. 42 Congjiang pigs were anew chosen for model validation by linear regression and correlation analysis of measured IMF and predicting IMF percentage. The result of regression analysis indicated that three independent variables which contained BFT and two image parameters of average gray (H6) and gradient entropy (H12) were significant in last model (P<0.05). The predictive equation is PIMF=6.443+0.064BFT+0.031H6-7.421H12, with determinate coefficient R2 of 0.369. The determinate coefficient R2 between the predictive value obtained by model and measured value of the validation set was 0.381. The root mean square error between predictive value and measured value of the validation set was 0.686. Correlation analysis showed that the pearson correlation coefficients and spearman correlation coefficients were 0.592 and 0.640 (P<0.001), respectively. Therefore, the regression model constructed in this study could be used to predict the living body of Congjiang pigs. Meanwhile, the experimental model provides a more convenient and effective nondestructive detection method for breeding with high IMF percentage of Congjiang pigs, which can reduce the breeding cost and shorten the breeding process, and promote the development of miniature pig's characteristic industry.