The effect of inclusion level and basal diet on the determination of the digestible and metabolisable energy content of soybean oil and its digestibility when fed to growing pigs

This experiment was conducted to determine the effect of inclusion level and type of basal diet on the digestible (DE) and metabolisable (ME) energy content of soybean oil and its digestibility when fed to growing pigs. Thirty-six barrows (Duroc × Landrace × Yorkshire weighing 34.2 ± 3.8 kg) were randomly allotted to a 2 × 3 factorial arrangement involving two basal diets and three levels of soybean oil (0%, 5% and 10%). One basal diet was based on corn and soybean meal. The other basal diet was based on corn starch and casein. The barrows were housed in individual metabolism crates to facilitate separate collection of faeces and urine, and were fed the assigned test diets at 4% of initial bodyweight per day. A 5-day total collection of faeces and urine followed a 7-day diet-adaptation period. The DE and ME contents of soybean oil were significantly affected by the dietary inclusion level (P < 0.05), but not by the type of basal diet. The DE contents of soybean oil at the 5% and 10% inclusion level were 34.99 and 37.63 MJ/kg, respectively, for the corn–soybean meal basal diet and 33.72 and 35.21 MJ/kg, respectively, for the corn starch–casein basal diet. The respective corresponding values for ME were 33.91, 37.07, 33.06 and 34.83 MJ/kg. The DE values calculated from regression equation were 38.05 and 37.85 MJ/kg, respectively, for corn–soybean meal and corn starch–casein basal diet. The DE value calculated from regression equation was greater than the values determined from the difference method for corn starch–casein basal diet. The value of endogenous loss for acid-hydrolysed ether extract was greater (P < 0.05) for corn–soybean meal basal diet than for corn starch–casein (13.06 g/kg of dry matter intake for corn–soybean meal basal diet and 1.37 g/kg of dry matter intake for corn starch–casein basal diet, respectively). The values of the true total tract digestibility and apparent total tract digestibility of soybean oil determined from the corn–soybean meal basal diet were not different from those determined from the corn starch–casein basal diet (true total tract digestibility: 97.1% and 95.4%; apparent total tract digestibility: 95.8% and 95.3%, respectively). In conclusion, the DE and ME values of soybean oil are affected by its inclusion level but not by basal diet. The type of basal diet did not affect the digestibility of soybean oil, but affected the endogenous loss of acid-hydrolysed ether extract for soybean oil.