Effect of the dietary electrolyte balance on the phosphorus-releasing action of phytase

Introduction

Phytate phosphorus, in its natural state in feed, forms complexes with different nutrients, including proteins, lipids, and minerals. Exogenous phytases not only release the phosphorus attached to the phytate acid molecule, but also the phosphorus attached to other nutrients, such as calcium and amino acids. The reduction of the cost of phytase in recent years, along with the increase in the cost of raw materials rich in phosphorus as animal protein, has led to great interest in using higher levels of phytase in broiler diets, since studies have shown an increase in phosphorus release with increasing levels of phytase (Shirley & Edwards)(2003). Recent studies indicate that phytase could influence sodium metabolism; however, Goodgame et al. (2011) could not demonstrate a relationship between the dietary needs of sodium and levels of phytase supplemented when sodium bicarbonate was used as the main source of sodium. This study was carried out to evaluate the use of phytase supplemented at normal and higher levels and its possible relationship with the Dietary Electrolyte Balance (DEB).

Materials & Methods

Nutritionally complete diets (Rostagno, 2005) of corn and soy meal were formulated to contain 0.12% of non-phytate phosphorus (FNF) and two different levels of BED through the addition of NaCl or NaHCO₃. Diets containing two levels of BED were supplemented with 0, 500, 1000 or 2000 FTU/Kg of phytase (Quantum Phytase 5000XT). A phosphorus response curve was prepared with diets supplemented with increasing levels of non-phytate phosphorus, in the form of Bi-calcium phosphate, at 0 to 0.30% in 0.05% increments. BB male chicks of a commercial line (Cobb 500) were placed in cages (5 birds per cage) until day 18 days and fed different diets. Drinking water and food were supplied ad libitum during the experiment. Average weight by cage was measured at the beginning of the experiment and on day 18, when food consumption was determined. At the end of the experiment the birds were slaughtered and all the toes were used for ash determination. The tibias of two birds were used to determine break strength. Regression analysis was used to estimate the phosphorus equivalent value by phytase (PhEV) (Yan et al., 2005). Data were analyzed using ANOVA (SAS, 1991) in form of a 2 x 4 factorial array of treatments, with two BED levels and four levels of phytase supplementation, as well as the interaction thereof. P< 0.05 was used to draw statistically significant values.

Results and Discussion

There were no significant differences in BW, FCR, mortality, ash, and tibia break force or PhEV due to BED in the diet (Table 1). As expected, incremental levels of phytase significantly improved BW, FCR, ash and break force (P < 0.05). The PhEV increased with increasing levels of phytase. We found no significant interactions between the BED and the level of supplementation of phytase for any of the analyzed parameters.

Table 1. Effects of dietary electrolyte Balance (BED) and levels of Phytase on performance and Phosphorus equivalence value (PhEV) of phytase

	18 d BW (kg)	0-18 d FCR	0-18 d Mortality (%)	Ash %	Break force (kg)	PhEV
BED (meq/kg)
214	0.548	1.401	9.33	10.55	10.16	0.128
264	0.536	1.396	5.70	10.54	9.89	0.116
Phytase (FTU/kg)
0	0.454^c	1.419^a	17.50^a	8.79^d	5.87^d	0.030
500	0.551^b	1.419^a	2.91^b	10.34^c	9.23^c	0.089
1000	0.557^b	1.407^a	6.00^b	11.18^b	11.26^b	0.174
2000	0.607^a	1.350^b	3.66^b	11.86^a	13.75^a	0.279
BED	Phytase
214	0	0.458	1.419	21.67	8.72	6.04	0.030
214	500	0.552	1.414	3.33	10.20	9.01	0.113
214	1000	0.565	1.401	5.00	11.22	11.78	0.180
214	2000	0.617	1.369	7.33	12.08	13.82	0.232
264	0	0.450	1.418	13.33	8.86	5.71	0.030
264	500	0.551	1.424	2.50	10.49	9.46	0.127
264	1000	0.548	1.412	7.00	11.14	10.74	0.164
264	2000	0.597	1.332	0.00	11.65	13.68	0.218
SEM		0.008	0.007	1.533	0.145	0.365	0.008

^{abcd Values in the same column with different superscript differ significantly (P≤0.05).}

Conclusions

The results suggest that there is no association between BED levels normally used in broilers and the activity of phytase in poultry in the first stage of growth. Consistent with previous studies, the increase in the levels of Phytase above levels normally used significantly improved the productive performance of birds.

Bibliography

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