Software version 1.42 gave significantly different results than both 1.44 and 1.45 for all body compartments (). Results for BMC and FM were significantly higher with 1.42, than either 1.44 or 1.45 (P<0.001). LTM and BMD were significantly lower with 1.42 than with either 1.44 or 1.45 (P<0.001). Compared to carcass values, both newer versions still significantly overestimated FM (P<0.001), however the extent of the overestimation was much reduced (v1.44, 0.19 ± 0.05g; v1.45, 0.21 ± 0.05g). Whereas v1.42 underestimated LTM (compared to carcass), both newer versions significantly overestimated LTM (P<0.001, v1.44, 1.34 ± 0.06g; v1.45, 1.31 ± 0.06g). Bone ash was significantly underestimated in both 1.44 (−0.039 ± 0.002g) and 1.45 (−0.038 ± 0.002g) (P<0.001). None of the body compartments were significantly different between versions 1.44 and 1.45 (P>0.05).
Means and standard deviations of the body composition parameters from carcass analysis and using two versions of software. Ranges are presented in parentheses.
Results for FM from all three software versions were significantly related to carcass fat (P<0.001, r2>0.77). None of the slopes were significantly different than one (P>0.10), however the intercept of the relationship between version 1.42 and carcass fat was significantly different than zero (P<0.05). All three software versions significantly overestimated FM (P<0.001), however the extent of the overestimation was much greater for 1.42 (2.19 ± 0.06g) than for either 1.44 (0.19 ± 0.05g), or 1.45 (0.21 ± 0.05g).
The relationship between DXA LTM and chemical LTM was highly significant with all three software versions (P<0.001, r2>0.98). None of the relationships had intercepts that were significantly different than zero (P>0.05), however, the slope of the relationship between DXA LTM using 1.44 and chemical LTM was significantly less than one (P=0.03). Whereas 1.42 had significantly underestimated LTM (−0.58 ± 0.05g P<0.001), versions 1.44 and 1.45 significantly overestimated LTM (1.34 ± 0.06g and 1.31 ± 0.06g respectively, P<0.001).
DXA BMC was significantly related to chemical bone ash using all three software versions (P<0.001, r2>0.96). However, the intercepts using all three versions were significantly different than zero (P<0.01), and the slope of the relationship using version 1.42 was significantly less than one (P=0.003). Whereas 1.42 slightly overestimated bone ash (0.005 ± 0.002g, P=0.065), versions 1.44 and 1.45 both significantly underestimated bone ash (−0.039± 0.002g and −0.038 ± 0.002g respectively P<0.001).
New prediction equations were developed based on the above relationships for versions 1.44 and 1.45 and are presented in (for v1.45 only). Backward elimination regression was used entering DXA values of FM, LTM, and BMC into all the models. Chemical FM was best predicted by DXA FM for both 1.44 (r2=0.80, P<0.001, RMSE=0.26g) and 1.45 (r2=0.79, P<0.001, RMSE=0.27g). Chemical LTM was best predicted by a model containing both DXA LTM and FM for both 1.44 (r2=0.99, P<0.001, RMSE=0.23g) and 1.45 (r2=0.99, P<0.001, RMSE=0.24g). Chemical bone ash was best predicted by the model including DXA BMC for 1.44 (r2=0.97, P<0.001, RMSE=0.009g) and 1.45 (r2=0.96, P<0.001, RMSE=0.01g).
Prediction equations for chemically extracted carcass components from v1.45 data.
These new equations for versions 1.44 and 1.45 are different from those developed for 1.42 [1
]. To assess the effect of these different equations, predicted FM and LTM were calculated for data analyzed in version 1.45 using both the 1.42 equations and the 1.45 equations and the results compared to carcass FM and LTM. This was repeated for 1.44, using 1.42 and 1.44 equations, but only the results for v1.45 are presented as they are the same. Predicted FM using the software specific equations was not significantly different than the carcass FM (). However, using the equations developed for 1.42 resulted in significantly lower FM than either carcass or software-specific predicted FM (P
<0.001). In addition, the predicted FM using 1.42 was actually less than 0. In the comparison of carcass LTM to the predicted LTM using software specific equations, there was no significant difference (P
>0.05) (). However, using the 1.42 equation to predict LTM analyzed in version 1.45 resulted in significantly higher LTM (P
<0.001). Predicted bone ash using either 1.44 or 1.45 was not significantly different than carcass bone ash (P
Residual plot of carcass fat against the difference between DXA fat (using v1.45) and carcass fat mass (solid symbols). Open symbols represent the difference calculated with the predicted DXA fat (using v1.45 equation).
Residual plot of carcass lean mass against the difference between DXA lean (using v1.45) and carcass lean mass (solid symbols). Open symbols represent the difference calculated with the predicted DXA lean (using v1.45 equation).
Residual plot of carcass bone ash against the difference between DXA BMC (using v1.45) and carcass bone ash (solid symbols). Open symbols represent the difference calculated with the predicted DXABMC (using v1.45 equation).