Body composition analysis of the pig by magnetic resonance imaging

Magnetic resonance imaging (MRI) was used to measure, in vivo, the volume of several organs and tissues of a total of 111 pigs (males and females) ranging in BW from 6.1 to 97.2 kg. In one experiment the in vivo MRI volumes were compared to tissue or organ weights obtained by dissection. For internal organs, the correlation (R2) between MRI volume and dissected weight ranged from 0.64 (SE of estimation = 65 g) for the heart to 0.90 (SE of estimation = 125 g) for the liver. The MRI volume of the kidneys was approximately 10% less than the dissected weight, whereas the MRI volumes of the heart, liver, and brain exceeded the weights of dissected organs by 13, 17, and 26%, respectively. For fat and muscle tissues, the correlation between MRI volume and dissected weight ranged from 0.82 (psoas muscle) to 0.97 (total right ham muscles). The MRI volume of the backfat and shoulder muscles exceeded the dissected weights by approximately 2%, whereas the MRI volumes of the ham muscles, jowl fat, longissimus muscle, and psoas muscle were 2, 8, 18 and 20% less than their respective weights. In another series of experiments, MRI volume measurements of fat and muscle regions (Jowl fat, backfat, shoulder muscles, LD muscles, psoas muscles, ham muscles, a 10-cm section of the longissimus muscles and overlying fat, and a 15-cm section of the ham muscles and overlying fat) were evaluated by stepwise regression for the prediction of total body fat, lean, and protein. The best prediction of percentage total body fat was obtained using the fat volume from the 10-cm section of longissimus muscle and the fat:muscle ratio from the 15-cm section of the ham (R2 = 0.9). The best prediction of percentage total body protein was obtained using a combination of the volumes (as a percentage of BW) of jowl fat, backfat, shoulder muscle, and ham muscle (R2 = 0.62). The combination fat volume from the 10-cm section of longissimus muscle, the fat:muscle ratio from the 15-cm section of the ham, and the lean volume percentage from the 15-cm section of ham provided the best prediction of the percentage of total body lean (R2 = 0.88).