The benefits of high phytase doses on the growth and feed efficiency of broilers have previously been demonstrated and they appear to be dependent on the ability of phytase to degrade phytic acid rapidly in the digestive tract. This study evaluated the ability of Buttiauxella or E. coli phytase to increase the growth and feed efficiency of broilers beyond traditional dose recommendations. In the first analysis, data from seven broiler trials were used to determine dose response relationships with a Buttiauxella phytase at inclusion levels ranging from 500 to 2000 FTU/kg. Phytase was added to a negative control (NC) diet that was deficient in available P, Ca and energy and a nutritional adequate positive control (PC) diet was used as a reference. A strong linear response (P ≤ 0.005) in ADG, FCR and energy conversion was observed with increasing phytase level from 0 (NC) to 2000 FTU/kg in all phases. Overall 42 day data showed that 2000 FTU/kg phytase outperformed the PC with higher (P < 0.05) ADG and ADFI. Ileal P digestibility plateaued at 1000 FTU/kg. Bone ash was significantly reduced in the NC diet compared to the PC and was recovered in all phytase treatment groups. The best energy conversion ratio (MJ/kg BWG) was observed at 1000 FTU/kg, being 0.6 MJ (143 kcal) and 0.8 MJ (191 kcal) lower per kg BWG compared to the PC and NC, respectively. Phytase supplementation at 2000 FTU/kg reduced the rearing period to market size (3 kg live BW) by 2.5 days compared to the PC. In the second analysis, data from four trials were analysed to compare the efficacy of Buttiauxella and E. coli phytases; each phytase was included at 250, 500 and 1000 FTU/kg, respectively, in a NC diet that was deficient in available P, Ca, and energy, with respective PC diet as a reference. Both phytases improved (P < 0.05) growth and feed efficiency of broilers compared to the NC. Buttiauxella phytase at 1000 FTU/kg improved growth and reduced body weight corrected feed conversion (FCRc) by 4 points compared to the PC, and improved efficacy compared to E. coli phytase. It can be concluded that high doses of phytase at 1000-2000 FTU/kg can be beneficial in broiler production.
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 .
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).
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.
Amerah AM, Plumstead PW, Barnard LP & Kumar A (2014) Poultry Science 93: 906-915.
Cowieson AJ, Ravindran V & Selle PH (2008) Poultry Science 87: 2287-2299.
Lean IJ, Rabiee AR, Duffield TF & Dohoo IR (2009) Journal of Dairy Science 92: 3545-3565.
Plumstead PW, Kwakernaak C & van der Klis JD (2012) Poultry Science 91(Suppl. 1): 91.
Selle PH & Ravindran V (2007) Animal Feed Science and Technology 135: 1-41.
Truong HH, Yu S, Peron A, Cadogan DJ, Khoddami A, Roberts TH, Liu SY & Selle PH (2014) Animal Feed Science and Technology 198: 248-256.