Effect of graded levels of supplementary phytase in diets with and without rapeseed meal on energy utilisation, nutrient availability and phytate degradation in young turkeys

V. Pirgozliev 1, S.C. Mansbridge 1, S.P. Rose 1, C.A. Brearley 2, M.R. Bedford 3 - 1 National Institute of Poultry Husbandry, Harper Adams University, Newport, Shropshire, UK - 2 School of Biological Sciences, University of East Anglia, Norwich, Norfolk NR4 7TJ, UK - 3 AB Vista, Marlborough, Wiltshire, UK

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Application of dietary enzymes, including phytase, protease, and carbohydrases, alone or in combination, to facilitate phosphorus, protein, and energy utilization is a common approach to quality improvements of rapeseed meal (RSM) in poultry diets.

Most studies to date have been conducted in broilers. Thus there is a scarcity of information as to the use of enzymes on RSM in turkey rations. In particular, little is known about the effect of phytase on phytate degradation in RSM rich diets when fed to turkeys, an observation which is particularly pertinent given supplementary phytase seems to produce different results in chickens and turkeys. In addition, there is a lack of information on the effect of graded levels of exogenous phytase on N-corrected apparent metabolisable energy (AMEn), dry matter (DMR), nitrogen (NR), phosphorus (PR), calcium (CaR) and phytate degradation of RSM rich diets when fed to turkeys.

Therefore, the objective of this experiment was to examine the effect of graded levels of exogenous phytase on the energy utilisation, nutrient availability and phytate degradation when feeding diets with and without RSM to young turkeys.

Animals and experimental design

A basal diet, with low AvP (AvP in the diet was calculated to be 0.53%) and low Ca (Ca in diet was calculated to be 1.12%) was produced (Table 1). Another diet was produced by mixing 80% of the basal diet and 20% of industry produced RSM. The two basal diets were then split in four parts each and phytase enzyme was added at 0, 500, 2500 and 12500 FTU per kg diet respectively. Nutrient availability was examined in the experiment from 27 to 35 d age using 96 female BUT Premium turkey poults (Faccenda Foods Ltd., Dalton, UK). Each diet was fed to 6 pens (two birds each) following randomisation. Excreta were collected for the last 3 days of the study. All laboratory analysis and calculations were performed following standard procedures. Data were analysed by 2 x 4 factorial design ANOVA.

Results and discussion

There were no (P>0.05) phytase by RSM interactions for any of the variables presented in Table 2. Results in this study show an improvement of most of the studied variables by phytase supplementation. There was a positive quadratic relationship (P<0.05) between dietary phytase activity and daily FI, as dosage of 2500 FTU was the optimum for FI (Table 2). There was a similar tendency between phytase activity and daily WG (P=0.053), but no response for FCR (P>0.05) was observed. The AMEn of the basal diet and the RSM containing diet (with no phytase) were close to the calculated values. There was a positive linear relationship between phytase activity and dietary AMEn (P<0.05) (Table 2). There was a positive linear relationship between phytase activity and dietary DMR (P<0.05), NR (P<0.05), CaR (P<0.001) and PR (P<0.001) (Table 2). The data with INS and inositol phosphate isomers are presented in Table 2 with all parameters responding quadratically to phytase addition

Despite the relatively short feeding period, daily FI and WG of turkeys improved in agreement with previous reports. The linear improvement in dietary AMEn with dietary phytase increase is in agreement with Pirgozliev et al. (2007). In the reported study, the retention coefficients of DM, N, Ca and P responded in a linear dose dependent manner to phytase supplementation. This increase in available energy and nutrient retention was negatively correlated to the reduction of the concentration of IP6 and the rest of the studied IP isomers in this experiment.

The theory of enzymatic breakdown of phytate compounds distinguishes between the liberation of phytate molecules from complexes with other tissue components and enzymatic cleavage of phosphate residues on the myoinositol ring. The stepwise manner of dephosphorylation of IP6 could lead to a release of different myoinositol isomers and phosphates.

The results in this study suggest that super levels of phytase are capable of reducing the IP6 concentration in the excreta by 97%. Similarly, IP5 concentration in the excreta was decreased by almost 99% of the NC value. Both, IP6 and IP5, are highly potent chelaters of minerals and may interfere with digestion of protein. This may explain the positive linear improvement in AMEn with increasing level of supplementary phytase, in keeping with the theory that a high IP6 concentration can inhibit pepsin secretion and therefore protein digestion.

In agreement with Bedford and Walk (2016) IP4 and IP3 initially increased by 45% and 14%, respectively with a standard 500 FTU/kg phytase, however, superdosing phytase at 12.500 FTU/kg phytase resulted in a reduction of 32% and 44%, respectively, from the negative control.

References are available on request

From the Proceedings of the 13th Turkey Science and Production Conference