PREDICTION OF THE APPARENT DIGESTIBLE ENERGY VALUE OF FATS GIVEN TO PIGS

Data from experimental programmes designed to investigate designed to investigate the effect of chemical structure of fats upon their apparent digestible energy (DE) value for pigs were subjected to regression analysis. For growing pigs, over the approximate live-weight range 30 to 90 kg, 25 data points were available, with fats evaluated having a range in the ratio of unsaturated to saturated fatty acids (U/S) from 0.66 to 15.67 and in free fatty acid (FFA) content from 8 to 818 g/kg. Sixteen data points were available for young pigs of approximately 12 kg live weight with a range in U/S from 0.62 to 5.71 and in FFA content from 54 to 756 g/kg. The wide range of values for U/S and FFA content had been obtained by blending different fats and, therefore, represented both the range and extremes likely to be found in the formulation of pig diets. Derivation of prediction equations for DE were based upon a series of non-linear regresssion analyses employing, in sequence, U/S, U/S + FFA content and U/S X FFA content. The DE of fats could be predicted from U/S and FFA content with equations accounting for 0.802 and 0.768 of the variation in DE values for growing and young pigs respectively. The most appropriate equation for pigs of all live weights employed U/S and FFA content additively (U/S + FFA content). The equation for growing pigs was DE (MJ/kg = 36.898 -(0.0046FFA (g/kg)) - 7.33e(-0.906U/S) and for young pigs was DE (MJ/kg) = 37.890 - (0.0051FFA (g/kg)) - 8.20e(-0.515U/S). Comparisions revealed that differences between the two age groups, with lower values achieved with younger pigs, were more pronounced the lower U/S and the higher FFA content of the fat.