INVESTIGATION ON BODY-COMPOSITION OF GROW ING LAMBS BY MEANS OF MAGNETIC-RESONANCE-IMAGING (MRI)

In this investigation Magnetic Resonance Imaging (MRI) was applied to estimate body composition (total amount of lean and fat, percentage of lean and fat) of live lambs weighing between 10 and 50 kg. Mutton typ e lambs and their crosses with finnsheep were selected to derive equat ions for lambs weighing less than 30 kg (group 1, n = 49) and for lamb s weighing more than 30 kg (group 2, n = 84). Total dissection of the left carcass side into lean, fat, and bone served as a reference. Afte r editing, the MR images were statistically analysed without backgroun d, bones, and organs. The remaining set of pixel data was subjected to cluster analysis to generate lean and fat areas of the MR images. For deriving the equations. a multiple stepwise regression analysis was c arried out with computed cluster areas and live weight as independent variables. Coefficients of determination for group 1 (less than or equ al to 30 kg) were: R(2) = 0.96 for total amount of lean (SEE = 160 g), R(2) = 0.78 for percentage of lean (SEE = 1.57 %), R(2) = 0.96 for to tal amount of fat (SEE = 84 g) and R(2) = 0.86 for percentage of fat ( SEE = 1.49 %) and for group 2 (> 30 kg): R(2) = 0.91 for total amount of lean (SEE = 261 g) R(2) = 0.91 for percentage of lean (SEE = 1.60 % ), R(2) = 0.94 for total amount of fat (SEE = 195 g) and R = 0.90 for percentage of fat (SEE = 1.64 %). These functions were then applied to estimate body composition of another experimental group of 52 lambs,w hich were scanned five times at the age of 8, 11, 14, 17, and 20 weeks . The data series of this study were used to calculate allometric coef ficients. This allometric coefficients showed. that total amount of le an and live weight grow at the same rate (b = 1), while fat increases faster than live weight. The allometric coefficient for the amount of fat for female lambs was b = 1.8 and for male lambs b = 1.6.