Comparison of Three Different Phytase Products on Broiler Performance and Toe Ash

Phosphorus (P) is an essential nutrient in metabolic processes and the third most costly nutrient in monogastric feed after energy and protein. All plant ingredients contain phytate (salt of phytic acid, myo-inositol hexakisphosphate, IP6) which is a source of phosphorus for farm animals. However, phytate has poor bioavailability for monogastric animals due to inadequacy of endogenous phytase activity and lower microbial degradation capacity in the digestive tract (Li et al., 2022). This leads to routine supplementation with inorganic P sources to animal diets which not only increases feed cost but also P excretion resulting in environmental pollution. Moreover, phytate possesses substantial antinutritional impact, due to its interactions with other components in the digestive tract, forming insoluble complexes with positively charged mineral ions, such as calcium, and other trace minerals as well as amino acids (Selle et al. 2012) causing a negative impact on overall feed digestibility.

The recent significant inflation in the cost of feed ingredients, along with the global demand on sustainability, is driving the animal industries to review P levels in diets and to search for more effective phytases with higher efficacy to enhance P utilisation. This study aimed to compare the efficacy of two new-generation commercial phytase products versus a currently available commercial phytase.

The study was conducted following a complete randomised design, plus a positive control (PC) and a negative control (PC), which contained no added phytase, to serve as a baseline for the comparison. In total of 4,356 day-old male broiler chicks (Lohmann Indian River) were allocated into 11 dietary treatments, consisting of PC and NC, plus 3 different phytases (A, B and C) at 3 application dosages (250, 500 and 1000 FTU/kg diet). The PC diet was formulated to meet the requirements of nutrients to support normal growth as specified by the breeding firm (Lohman Indian River), and the NC was formulated to create marginal deficiency of nutrients in order to observe performance differences, whilst avoiding significant losses of growth and health of the birds. The levels of down-spec were ME 0.084 MJ/kg, 2% in digestible amino acids, and 0.2 %-unit in calcium and available and finally 0.03 %-unit in sodium. Each treatment had 11 replicates with 36 birds per replicate, in total 396 birds per treatment. The birds were raised in floor pens of 1.70 x 1.44 m2 , in an enclosed pen house. As the purpose of the study was to evaluate P and phytase efficacy, a 2-phase feeding program was chosen: 1-21 days of age as starter and 22-35 days of age as finisher. Fine crumble was provided during the starter and pellet was given during the finisher phase. The birds had free access to feed and water.

Diet formulation is shown in Table 1. Three commercial phytase samples (A, B and C) were collected from the market in Southeast Asia. Phytase A and B both are newly launched bacterial consensus 6-phytase variant, expressed in Trichoderma reesei, and C was an enhanced E. coli phytase. All the three phytase samples were analyzed according to standard procedure and all samples met their declared specification.

The birds were weighed on a pen basis on days 0, 21 and 35. Feed intake was measured at the end of each phase, and feed conversion ratio (FCR) was calculated (including live weight and mortality correction) accordingly. The performance index was calculated at day 35. Mortality, culling number, and dead weights were recorded daily. Toe ash was measured at day 21 over one sample pooled by 3 birds/pen (total of 121 pooled toe ash samples). Carcass % and abdominal fat pad were measured at day 35 over a total of 363 samples, 3 birds/pen.

Table 2 shows the results of performance and toe ash contents at the end of the starter phase. As expected, all performance parameters (FI, BW and FCR) of the PC group reached their breeder standard, confirming adequate diet formulation and trial management. Significant decrease in performance was observed in the NC. The reduction of the three essential nutrients led to a decrease of feed intake (P < 0.05), and consequently lower net gain (P < 0.05), and performance index (P < 0.05) and increase in FCR (P < 0.05). Significantly lower (P < 0.05) toe ash content in the NC groups with a very low mortality rate indicates that the final avP level in NC was appropriate. All performance parameters were improved with phytase supplementation and there were no interactions between phytase source and dose (P > 0.05). Among the phytases tested, Phytase A displayed a tendency of more effectiveness over the other two products. Moreover, the results showed a steady and significant (P < 0.05) dose response in terms of weight gain, FCR and PI.

Table 3 presents the performance results and carcass measurements at the end of the study. While the performance of the PC group met the breeder standard, the reduction in the essential nutrients resulted in numerical decreases in feed intake, and net gain, and a significant decrease in performance index (P < 0.05). FCR was maintained, most likely due to a well-balanced reduction of all major nutrients, leading to “eat less and grow less” situation and therefore similar feed efficiency to the PC group. The sub-adequate performance due to the down-spec nutrients created room for the birds to reflect the effect of additional phosphorus and nutrients released by phytases, which improved FCR in a quadratic manner as reported by Jlali et al. (2022). Weight gain, and PI were also improved (P < 0.05) over the NC group.

No statistical differences were observed among the phytase products in terms of performance. Phytase A yielded significantly more breast muscle (P < 0.05) than the other two products, with less abdominal fats (P < 0.05). This may be explained by a more efficient digestion and utilisation of dietary energy for protein synthesis rather than fats. On the other hand, a phytase dose response was observed as the groups receiving higher doses grew more weight, at significantly lower FCR (P < 0.05) and higher PI (P < 0.05), these results are well in line with the findings of Li et al. (2022) and Jlali et al. (2022).

In conclusion, the results demonstrated that the supplementation of all three phytase products was effective in restoring performance and toe ash, and there are clear dose responses from 250, 500 to 1000 FTU/kg. Among the three products, Phytase A appears to have displayed more effectiveness during the starter phase, but such advantage did not last until the end of the growth cycle. Moreover, the birds fed on Phytase A produced more breast muscle and less abdominal fat.