Abstract:
1α-Hydroxycholecalciferol (1α-OH-D3) is a synthetic cholecalciferol derivative that is rapidly hydroxylated into 1α,25-dihydroxycholecalciferol, the biologically active form of cholecalciferol. 1α,25-Dihydroxycholecalciferol plays a critical role in several biological processes and is important for the regulation of several genes involved in calcium (Ca) and phosphorus (P) absorption. Phytase is an enzyme that hydrolyses phytate and improves the digestibility of Ca and P in the small intestine. The objective of this study was to establish the effects of 1α-OH-D3 in combination with phytase on apparent ileal digestibility (AID) of Ca and AID P. To achieve this a digestibility trial was conducted on broilers at two different ages, days 10 and 23 (D10 and D23), respectively. Treatments were arranged in a 3 × 3 factorial with three 1α-OH-D3 doses (0, 2.5 and 5 µg 1α-OH-D3/kg feed) × three phytase doses (0, 500, 1000 FTU phytase/kg feed). Treatment diets were prepared by adding 0, 2.5 or 5 µg 1α-OH-D3/kg and/or a 6-phytase, which is a novel consensus bacterial 6-phytase variant, expressed in Trichoderma reesei, at 0, 500 or 1000 FTU phytase/kg feed. Each treatment was replicated 11 times on both D10 and D23 with 8 birds/replicate for D10 and 6 birds/replicate for D23. On the respective sampling days, ileal digesta was collected, frozen, freeze-dried and ground to pass through a 0.25mm screen before being analysed for dry matter, Ca, P, and titanium. The data was analysed with a full factorial using the JMP 16.0 statistical package where block was included as a random effect and means were separated using a protected Tukey HSD test at P<0.05. Both 1α-OH-D3 and phytase improved AID Ca, AID P, digestible Ca (dCa) and digestible P (dP). There was no difference in birds that were fed diets that were supplemented with 2.5 µg and those supplemented with 5 µg 1α-OH-D3/kg feed for any of the parameters measured on D10 and D23, suggesting that there is no added benefit on Ca and P digestibility when increasing the supplementation of 1α-OH-D3 from 2.5 µg to 5 µg 1α-OH-D3/kg feed. Phytase improved AID Ca, AID P, dCa and dP in a stepwise fashion on both D10 and D23 when supplemented into the diet of birds at 500 or 1000 FTU phytase/kg. There was no interaction between 1α-OH-D3 and phytase for any of the parameters measured on D10 or D23.
