Investigating possible impact, and interaction, of phytase supplementation during pre-experimental and experimental phases on assay of true phosphorus pre-caecal digestibility and total tract retention

ABSTRACT

1. Two experiments were conducted to investigate whether the use of phytase in the pre-experimental or experimental phases of true pre-caecal phosphorus digestibility (TPD) assay influenced the assayed TPD values. In experiments 1 and 2, broiler chickens were randomly allocated to 12 treatments in a 2 × 2 × 3 factorial arrangement. The factors were pre-experimental phytase supplementation (+ or -), experimental phase phytase supplementation (+ or -) with varying soybean meal inclusion levels (450, 560, or 670 g/kg).

2. The diets in the pre-experimental phase were based on maize-soybean meal, whereas the diet used during the experimental phase was semi-purified, with soybean meal as the only source of P. Both TPD and true phosphorus retention (TPR) were determined using regression for the P output (g/kg, dry matter basis), pre-caecal or total tract, against P intake (g/kg). Data for TPD and TPR were analysed as a 2 × 2 factorial (with or without pre-experimental or experimental phase phytase).

3. In both experiments 1 and 2, there were no significant effects for pre-experimental phytase supplementation nor interaction of pre- and experimental phytase supplementation on any of the pre-caecal digestibility responses. Phytase supplementation during the experimental phase increased (P < 0.01) pre-caecal P digestibility and retention, as well as digestible and retained P intake, and decreased (P < 0.01) P output.

4. In experiment 1, pre- and experimental phytase supplementation increased (P < 0.01) the coefficient of TPR. In experiment 2, there was no significant effect of pre-experimental phytase supplementation on coefficient of pre-caecal TPD. However, phytase supplementation in the experimental phase increased (P < 0.01) the coefficient of pre-caecal TPD.

5. In conclusion, whether or not phytase was supplemented to a P-adequate diet in the pre-experimental phase of the TPD assay, it had no influence on assayed TPD or TPR value.

KEYWORDS:

• True phosphorus digestibility assay
• pre-experimental phase
• experimental phase
• phytase

Acknowledgements

The assistance of Lindsay Rackett, Trevor Ard, Yang Lin, and Iyabo Oluseyifunmi for animal care and chemical analysis are gratefully acknowledged. John M., Palmer III received part funding for Experiment 1 from CAES (College of Agricultural and Environmental Sciences) Undergraduate Research Initiative and CURO (Centre for Undergraduate Research Opportunities) Research Assistantship, both of the University of Georgia.

Disclosure statement

No potential conflict of interest was reported by the author(s).