The effects of pre-pellet cracked maize and phytase inclusions in maize-soy diets with three levels of crude protein (22, 19.5 and 17%) evaluated via a Box-Behnken response surface design

Reducing crude protein (CP) levels by replacing soybean meal with complementary amino acids and grain in diets for broilers may generate economic, environmental and flock welfare benefits; however, broiler performance is usually compromised. Phytase (PHY) has been reported to enhance amino acid digestibility and absorption which may be facilitated by enhanced gizzard functionality. Thus, the effects of pre-pellet cracked maize (CM; 0, 15 and 30%) and PHY (0, 750 and 1500 FTU/kg) in iso-energctic maize-soy diets with three levels of CP (22, 19.5 and 17%) were evaluated via a 13 treatment Box-Behnken design. Where appropriate, CM (mixed into diets prior to pelleting) replaced ground maize and PHY (Buttiauxella sp. expressed in Trichodcrma recsei; Axtra• PHY, Danisco Animal Nutrition) was added over the top. CP levels were reduced and complementary lys, met, thr, trp, val, arg, ile were included. Treatments were offered to 6 replicate cages (6 birds/cage) of male Ross 308 broiler chicks from 7-28 days post-hatch. Model prediction and response surface plots were generated in R. According to model predictions; weight gain, feed intake and FCR were all influenced by CM, PHY and CP level (P< 0.001 ). Reductions from 22% to 17% dietary CP in non-supplemented diets reduced weight gain, feed intake, relative gizzard weight and contents but improved fCR (P < 0.00 I). However, 30% CM inclusion to 17% CP diets increased gizzard weight and 1500 FTU PHY inclusion to 17% CP diets increased gizzard content. CM and PHY inclusion in tandem to 17% CP diets increased weight gain, feed intake and FCR; however, this FCR was still more efficient than broilers offered the non-supplemented 22% CP diet. Therefore, PHY and CM in tandem may improve performance of broilers offered reduced CP diets.