The Effect of High Phytase Inclusion in Laying Hen Diets

Supplemental phytase is routinely added to monogastric diets to increase the availability of phytate phosphours. Higher phytase inclusion levels (>2,500 FTU kg-1) are attracting interest as extra-phosphoric benefits are seen with increasing phytic acid hydrolysis. Phytic acid hydrolysis has been shown to increase protein, mineral and energy utilisation, reduce endogenous losses and increase the availability of myo-inositol. It is through these improvements that phytase has been shown to benefit broilers and pigs, but not layers. Four experiments were conducted to assess the effect of high phytase inclusion in the laying hen. In the first experiment, phytase was shown to increase the solubility of the diet within the gastrointestinal tract, and in particular the solubility of numerous minerals. Notably, calcium and phosphorus solubility were increased from 4 and 7.4 to 12.3 and 15.9 g soluble 100 g-1 total respectively within the duodenum. Phytase also increased the concentration of calcium, magnesium, zinc and manganese but not phosphorus within the blood plasma of laying hens. In the second experiment, phytase significantly improved the FCR of laying hens from 2.08 to 2.02 and had an additive effect with glucanase in terms of weight gained. The third experiment showed that higher phytase inclusion could increase egg mass in comparison to a positive control, negative control and standard phytase inclusion diet. Chickens fed a diet containing 4,000 FTU kg-1 produced 61.07g/d egg mass whereas birds fed a 250 FTU kg-1 produced just 58.62g/d. In the final experiment, phytase reduced laying hen FCR from 2.11 to 2.03 in the absence of betaine, but with betaine included in the diet phytase had a negative effect increasing FCR from 1.99 to 2.07. Throughout the four experiments phytase was shown to inconsistently benefit shell quality, which may be due to elevated dietary calcium levels in the second and third experiments. Finally, in the third and fourth experiments phytase was shown to increase the concentration of hepatic and circulating myo-inositol respectively. Birds fed diets containing 16,000 FTU kg-1 had hepatic concentration of myo-inositol greater than double those fed a diet with 250 FTU kg-1. This thesis has shown that high phytase inclusion can benefit laying hen performance which may allow dietary nutrient dilutions.