Impact of super-dosing phytase in diets fed to 40 kg, 60 kg and 80 kg pigs on phytate catabolism

Abstract Text:

Phytase is added to pig diets to release phytate-bound phosphorus, but may also release additional nutrients when fed at super-dosed levels.  One possible benefit of super-dosed phytase is the release of free inositol which may then be available for a variety of functions, including as a precursor of compounds involved in neurological signals, structure and function of cell membranes, and insulin sensitivity. Three experiments were conducted to determine the impact of super-dosing phytase on phytate catabolism. Thirty-two gilts were surgically fitted with t-cannulae at the terminal ileum and at average body weights of 39.7 ± 0.3 kg, 60.5 ± 0.5 kg, and 82.5 ± 0.7 kg, they were utilized in experiments 1, 2 and 3, respectively. The basal diets were based on corn and soybean meal with chromic oxide added at 0.4% as an indigestible marker. Feed was supplied at 3.2 times maintenance (NRC, 2012) for 16 d in each experiment: 10d adaption, 3d fecal collection and 3 d ileal collection.  The 4 dietary treatments contained phytase (Quantum Blue® 5G; AB Vista, Marlborough, UK) at 250 (CTL), 1000, 1750, and 2500 FTUs/kg, respectively. Feed and ileal digesta were analyzed for phytate and its catabolic derivatives. Data were analyzed using the MIXED procedure of SAS; pig was the experimental unit. In all 3 experiments, the concentration of phytate (IP₆) was reduced in a quadratic fashion with the addition of super-dosed levels of phytase. Concurrently, the concentration of inositol increased in a linear manner. As phytase levels increased, the concentration of IP₅ decreased in a quadratic fashion (P < 0.001). The concentrations of IP₄ and IP₃ increased at the lower levels of phytase and then decreased at the higher level. In conclusion, the addition of phytase to pig diets at super-dosed levels catabolizes phytate, resulting in increasing concentrations of inositol and reduced concentrations of phytate.

Table 1. Impact of super-dosed phytase on phytate (IP₆) and inositol concentration in ileal digesta (µmol/g)

Molecule	Phytase levels, FTU/kg					P-values
	CTL	1,000	1,750	2,500	SEM	Treatment	Linear	Quadratic
40 kg
- IP6	19.28	10.85	8.10	6.79	1.64	<0.001	<0.001	0.041
- Inositol	3.20	5.31	9.93	9.04	1.19	0.002	<0.001	0.219
60 kg
- IP6	18.02	9.00	5.43	4.87	1.19	<0.001	<0.001	0.002
- Inositol	2.69	4.42	8.50	11.46	1.77	<0.001	<0.001	0.633
80 kg
- IP6	18.00	7.72	6.46	5.20	1.62	<0.001	<0.001	0.012
- Inositol	1.56	4.31	5.12	6.12	1.02	<0.001	<0.001	0.178

Keywords: phytate, phytase, inositol