Impact of Particle Size, Thermal Processing, Fat Inclusion and Moisture Addition on Pellet Quality and Protein Solubility of Broiler Feeds

The present study evaluated the effect of feed particle size, thermal processing, several levels of fat inclusion and moisture addition on pellet quality and protein solubility in potassium hydroxide (KOH) in a corn, soybean meal and animal by products based broiler diets. The different processing factors were combined in a 2  4  4  2 factorial arrangement in an eight randomized block consisting of eight production series: two particle sizes (coarse: 1,041 microns and medium: 743 microns), four fat inclusion levels at the mixer (15, 25, 35 and 45 g/kg of feed), four moisture addition levels in the conditioner (0, 7, 14 and 21 g/kg of feed) and two thermal processing treatments (conditioner-pellet press treatment or conditioner-expander-pellet treatment) which resulted in 64 different processed feeds. For the determination of the pellet durability index (PDI), the amount of intact pellets and protein solubility determinations, eight feed samples (replicates) were collected for each treatment. The data were transformed using a variation of Box-Cox transformation in order to fit a normal distribution (p > 0.05). Adding moisture up to 21 g/kg of feed in the conditioner improved pellet quality of the diets (p < 0.05). Expansion of diets before pelleting improved (p < 0.05) PDI and amount of intact pellets by 26% and 31%, respectively, as compared to a simple conditioning-pelleting feed processing. Expander treatment (at 110 °C) decreased (p < 0.05) protein solubility in KOH from 686 g/kg to 643 g/kg total protein as compared to pelleting process (at 80-82 °C). The amount of intact pellets reduced from 773 g/kg to 746 g/kg of feed (p < 0.05) as particle size increased from medium to coarse grinding. Pellet quality was significantly reduced with fat inclusion levels higher than 35 g/kg of diet.