Effects of inclusion level on nutrient digestibility and energy content of wheat middlings and soya bean meal for growing pigs.

Two experiments were conducted to determine the effects of inclusion level of wheat middlings and soya bean meal on apparent total tract digestibility (ATTD) of energy and chemical components of these ingredients in growing pigs. Furthermore, the effects of the inclusion level on their contents of digestible energy (DE) and metabolisable energy (ME) were also determined by the difference method. In Experiment 1, six diets were fed to 36 growing pigs according to a completely randomised design. The basal diet was a corn-soya bean meal diet while the other five diets contained 9.6%, 19.2%, 28.8%, 38.4% or 48.0% of wheat middlings added at the expense of corn and soya bean meal. The measured digestibility of energy and most nutrients of wheat middlings increased (p < 0.05) with increasing levels of that ingredient. Equations were obtained to predict digestibility by inclusion level. At an inclusion level of 9.6% wheat middlings, their DE contents were significantly lower (8.9 MJ/kg DM) than for the higher levels (10.7 to 11.9 MJ/kg DM, p < 0.01). In Experiment 2, three diets were fed to 18 growing pigs according to a completely randomised block design. The basal diet was a corn-based diet while the other two diets were based on corn and two levels of soya bean meal (22.2% and 33.6%). The content of DE in soya bean meal did not differ at 22.2% and 33.6% inclusion levels (16.2 and 16.3 MJ/kg DM, respectively), but the digestibility of dry matter (DM), organic matter and carbohydrates was increased at a higher inclusion level (p < 0.05). This study revealed that the estimated digestibility of nutrients from soya bean meal and wheat middlings was affected by their dietary inclusion levels. For soya bean meal, the estimated energy contents was independent of its inclusion level, but not for wheat middlings. Therefore, the inclusion level of wheat middlings has to be considered for estimating their energy value.