Performance and Nutrient Digestability in Broilers in Response to Increasing Doses of Phytase

I. INTRODUCTION

Phytase has traditionally been used in broiler feed at a standard dose of 500 FTU/kg, but recent studies have reported extra phosphoric effects of high phytase doses in broilers (Selle and Ravindran 2007; Amerah et al., 2014). It is well known that phytate, the main phosphorous source in plant ingredients, is poorly available to poultry. Phytate can bind amino acids and minerals and reduce utilization of these nutrients. High phytase doses can further reduce the antinutritional effect of phytate and improve digestibility of amino acids and energy, resulting in improved animal performance. The objective of this study was to evaluate: 1) dose response of a new generation phytase (derived from Buttiauxella spp.) on performance and nutrient digestibility in broilers; 2) compare the efficacy of Buttiauxella phytase with an E. coli phytase, based on pooled data from several trials carried out by Danisco Animal Nutrition/DuPont.

II. MATERIALS AND METHODS

In the first analysis, data from seven trials were collected in a database, including five treatments: PC, NC and NC supplemented with 500, 1000 and 2000 FTU/kg Buttiauxella phytase. PC diets were formulated to meet nutritional requirements. NC diets were formulated with lower levels of energy, available P, and Ca (average 0.2 MJ/kg ME, 0.17 % available P and 0.15 % Ca lower compared to PC). Ross broilers were used and fed diets based mainly on corn and soybean meal. Average daily feed intake (AFDI), daily weight gain (ADG) and feed conversion ratio (FCR, g feed/ g gain) were analysed for starter phase (0-21 days) and the overall period of 0-42 days. Due to a significant difference of ADG between the PC, NC, and phytase treatments, body weight corrected feed conversion (FCRc) was calculated by correction of 3 points (0.03) for each 100 g body weight difference compared to the PC, in order to standardize the data for accurate comparison of treatment means. In addition, energy conversion was calculated to compare energy efficiency between treatment groups, as phytase was supplemented to the low energy NC diet. In the second analysis, individual data from four trials were collected in a database, including eight treatments: PC, NC and NC supplemented with Buttiauxella or E. coli phytase at 250, 500 and 1000 FTU/kg. PC diets were formulated to meet nutritional requirements. NC diets were formulated with lower levels of energy, available P, and Ca (average 0.2 MJ/kg ME, 0.17% available P and 0.16% Ca lower compared to PC).

Outlier removal was conducted and Tukey’s HSD test was used for means separation in the Fit Model platform of JMP 11 (SAS Institute Inc., Cary, NC, 1989-2013). Dose response from 0 (NC) to 2000 FTU/kg phytase was analysed using linear and quadratic models. The trial code was included in the model as a random effect, as this accounted for the underlying heterogeneity between studies (Lean et al., 2009).

III. RESULTS AND DISCUSSION

a) Dose response

Results on performance parameters during starter (0-21 d) and overall (0-42 d) phases are presented in Table 1. Increasing phytase inclusion level linearly improved ADG and FCR in both starter and overall phases. Overall performance data showed that 2000 FTU/kg phytase improved ADFI and ADG compared to the PC, and reduced body weight corrected FCRc by 3.4 and 18.6 points compared to the PC and NC, respectively. The NC had lower (P < 0.05) bone ash (%) compared to the PC, but all phytase treatment groups recovered bone ash to a level similar to the PC. The best energy conversion ratio was with 1000 FTU/kg phytase, which was 0.6 MJ (143 kcal) and 0.8 MJ (191 kcal) lower per kg body weight gain than the PC and NC, respectively. Supplementation of 2000 FTU/kg phytase reduced rearing days to reach a market size of 3 kg live body weight by 2.5 (Table 1). Reducing available P in the NC diets resulted in a decrease (P < 0.05) of ileal P digestibility (%) compared to the PC. Increasing phytase dose improved ileal P digestibility in both a linear and quadratic manner. However, it seems that the ileal digestibility of P and bone ash reached a plateau at 1000 FTU/kg phytase in broilers fed mainly corn and soybean meal based diets containing 0.24-0.27 % phytate. The further improvement on performance at 2000 FTU/kg phytase may indicate some extra phosphoric effect.

b) Comparison of two phytases

The results of the comparison of Buttiauxella with E. coli phytase are presented in Figure 1. NC diets showed reduced (P < 0.05) ADG, bone ash and increased FCRc compared to the PC. All inclusion levels of both phytases improved ADG and FCRc compared to the NC; no differences were seen compared to the PC, except with Buttiauxella phytase at 1000 FTU/kg, which significantly (P < 0.05) improved ADG and reduced FCRc (by 4 points) compared to the PC. Phytase at 500 and 1000 FTU/kg recovered bone ash to a level similar to the PC, even though phytase supplemented diets were 0.17 % and 0.15 % lower available P and Ca, respectively. In comparison, Buttiauxella phytase increased (P < 0.05) ADG and reduced FCRc (P < 0.05) compared to E. coli phytase, but there were no differences in ADFI and bone ash.

Table 1 - Effect of increasing phytase supplementation to the NC diet (with low energy (0.2MJ/kg), available P (0.17%) and Ca (0.15%)) on performance of broilers¹ .

Performance and Nutrient Digestability in Broilers in Response to Increasing Doses of Phytase - Image 1

The data from both analyses demonstrated a clear benefit of using increasing doses of phytase in broiler feed. The improved performance and feed/energy efficiency at the high doses indicated an extra phosphoric effect, for which there are several possible mechanisms of action. First, increasing phytase level can increase the degradation of phytate and reduce its antinutritional effects, including an increase in amino acid digestibility (Amerah et al., 2014). Secondly, phytase can reduce endogenous nutrient losses (Cowieson et al., 2008), which may also contribute to improved nutrient efficiency. In addition, phytase may have an impact on the ratio of protein and starch digestion rate, which may influence passage rate and feed efficiency (Selle, personal communication). Another factor that may be involved is the effect of phytase on sodium and glucose metabolism (Truong et al., 2014). Recently it has also been suggested that inositol released from phytate degradation may contribute to the extra phosphoric effect; however, the extent to which released inositol may influence a broiler’s performance needs further evaluation. The high efficacy of Buttiauxella phytase compared to E. coli phytase is in line with other publication (Plumstead et al., 2012). This may be explained by the fact that Buttiauxella phytase is more effective at a lower, broader pH range, resulting in a high degree of phytate degradation in the upper GI tract of animals. A recent study showed that phytate degradation was up to 88 % in broilers fed corn and soybean meal based diets supplemented with 1000 FTU/kg Buttiauxella phytase (Amerah et al., 2014).

IV. CONCLUSION

Buttiauxella or E. coli phytase at a level equal or above 500 FTU/kg replaced 0.17 % available P, 0.15 % total Ca and 0.2 MJ/kg ME in broiler diets and maintained performance similar to the PC. Phytase supplementation at 1000-2000 FTU/kg can further improve ADFI, ADG, feed and energy efficiency, and reduce rearing days to reach market size in broilers fed a low energy, available P and Ca diet. This indicates an extra phosphoric effect which provides potentially increased economic benefits. Both phytases were effective in improving performance of broilers; however, Buttiauxella phytase had a significantly higher efficacy (FCRc, P < 0.05) than E. coli phytase at 500-1000 FTU/kg.

Figure 1 - Comparison of Buttiauxella (But) and E. coli phytases on performance and bone ash in broilers fed test diets for 42 days, based on statistical analysis of data from 4 trials.