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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. |
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