IN-VIVO ESTIMATION OF BODY-COMPOSITION OF MATURE GILTS USING LIVE WEIGHT, BACKFAT THICKNESS, AND DEUTERIUM-OXIDE

Thirty-seven Duroc x (Yorkshire x Landrace) (DYL) and 21 Yorkshire x L andrace (YL) gilts were used to develop equations that predict body co mposition of replacement-age breeding swine. Before slaughter, gilts w ere weighed, ultrasonically scanned for 10th rib backfat thickness, an d infused with D2O (.25 g/kg live weight). The D2O space (kilograms) w as calculated from body water D2O concentration determined at equilibr ium (150 and 210 min after infusion). Regression models predicting emp ty body (Eb) components for DYL and YL groups were fitted using all po ssible variable combinations (D2O space, live weight, and[or] backfat depth). Variables selected in best-fit models for Eb water, protein, f at, and ash for data from DYL gilts differed from variables selected f rom data from YL gilts. Average prediction errors (kilograms; [predict ed residual sum of squares divided by n](1/2)) of best-fit equations w ere 2.37, 2.03 (Eb weight), 2.36, 1.66 (Eb water), 1.07, .47 (Eb prote in), and 2.76, 2.89 (Eb fat) for DYL and YL data sets, respectively. C ross-validation by applying DYL equations to YL data, and vice versa, resulted in larger prediction errors. Likewise, larger errors were obt ained when equations published elsewhere were applied to DYL and YL da ta sets. No cited source provided a set of equations that consistently minimized prediction errors of all Eb components of both DYL and YL g ilts, Results indicate that prediction equations using D2O space, live weight, and(or) backfat thickness are accurate in estimating body com position only in animals physiologically resemble the population in wh ich the equations were derived.