Effect of super dosing of phytase enzyme on carcass traits of broiler chicken

Introduction

Phosphorus ranks as the third most high-priced nutrient in poultry diets, following energy and protein (Adewoye and Akinfala, 2023) [9] . Majority of the plant-based phosphorus are bound to phytic acid, which poultry cannot efficiently break down due to limited endogenous phytase production (Bedford, 2000) [1] . As a result, a lot of the phytate phosphorus remains unused and ends up being excreted in the chicken's manure. Phytic acid is considered an antinutritional factor because of its strong chelating ability, which interferes with the absorption of minerals and other nutrients (Joudaki et al., 2023; Oliveira Borges et al., 2025) [7,12] . Exogenous phytase enzyme is added to poultry diets at a standard dose of 500 FTU/kg to replace about 0.12% of dietary phosphorus. Recently, super dosing of phytase has gained attention for its potential to release greater amounts of phosphorus, reduce residual phytate and produce lipotropic compounds that support improved nutrient absorption. These benefits include enhanced amino acid utilization, protection of the intestinal lining, lower epithelial cell turnover and reduced metabolic burden in broilers ( [3,18,10,4,15,11,19] . The present study aimed to investigate the impact of phytase super dosing in phosphorus-deficient diets on carcass traits in broiler chickens.

Materials and Methods

The experiment was carried out at the National Institute of Animal Nutrition and Physiology (NIANP), Bengaluru, India, using a completely randomized design involving four dietary treatments in broiler chickens. A total of 168 birds were divided into four dietary treatment groups. Each dietary treatment had six replicates and each replicates had seven chicks. The dietary treatments consisted of one positive control diet, Group I without any phytase enzyme (0.45% available P during starter and 0.40% during finisher phase), and three negative control diets-Group II, III, IV (0.32% available P during starter and 0.28% during finisher phase) were supplemented with commercial phytase @ 500, 2500 and 5000 FTU/kg diet, respectively. The trial period was divided into two phases: starter (1 to 21 days) and finisher (22 to 35 days). The diets were based on corn/soybean meal (Table 1), which allowed for the constant inclusion of the majority of ingredients with the exception of dicalcium phosphate. Excel-based feed formulation was used to create the diets, which were based on the Nutrient Requirement of Poultry published by ICAR (2013) [5] using Excel-based feed formulation. At experimental livestock unit of institute, chicks were housed in battery cages as groups in random manner, fitted with heating arrangements, feeders, waterer and dropping trays, with 24 hr light, proper air ventilation and reared under standard managemental conditions. At the end of the trial, two birds from each replicate (12 per treatment group, totaling 48 birds) were randomly selected and humanely euthanized via cervical dislocation to evaluate carcass characteristics. The study was approved by the Institutional Animal Ethics Committee. Data were statistically analyzed using one-way ANOVA suitable for a completely randomized design, with treatment means compared using Tukey's HSD test. Statistical significance was set at p≤0.05 (SPSS Version 20.0, SPSS Inc., Chicago, USA).

NP-Normal Phosphorus diet LP-Low Phosphorus diet ** Calculated

Results and Discussion

The results obtained during the trial were presented in the Table 2. Broilers fed in the group III and IV ate more and gained more (p<0.05) than chicks fed in the group I and II during the trial period. The highest body weight was noticed in group IV (1.806±0.04 kg) and lowest in group II (1.463±0.05 kg). The carcass weight of broiler chicken was significantly higher in group IV receiving phytase 5000 FTU/kg diet and lower in group II receiving phytase 500 FTU/kg diet. The cut-up parts (breast, thigh, drumstick, back) weight followed the same trend of carcass weight.

In alignment with the present findings, Jain (2021) [6] observed a significant improvement (p>0.01) in the final body weight of broiler chicks supplemented with phytase at 500 FTU (T 1 ) and 1000 FTU (T 2 ) compared to the control group (T 0 ). Additionally, Broch et al. (2018) [2] reported that broiler growth performance responded to phytase supplementation in a quadratic manner (p<0.05) from day 1 to 42, with optimal results for body weight gain, feed consumption and feed conversion ratio achieved at inclusion levels of 2051, 1992 and 2101 FTU/kg, respectively. According to Shirley and Edwards (2003) [17] , high-dose phytase supplementation may offer beneficial effects through three main mechanisms: enhanced phosphate release or rebalancing of phosphorus to calcium ratios, reduced residual phytate to mitigate anti-nutritional effects and production of myo-inositol, which has vitamin-like or lipotropic properties due to the breakdown of phytate into more soluble lower esters. Lima et al. (2021) [19] recorded that varying levels of phytase (FTU) supplementation had a significant influence on carcass traits, particularly thigh yield (p = 0.027) and breast yield (p = 0.032). Their findings suggested that inclusion of 1500 FTU/kg and 1000 FTU/kg phytase resulted in the highest thigh and breast yields, respectively, in 45-day-old broilers. Similarly, Jain (2021) [6] observed a significant improvement in carcass characteristics of Kadaknath birds with phytase supplementation. Key parameters such as edible carcass yield, breast and thigh portions, meat and bone weights and meat-to-bone ratio were significantly enhanced (p>0.01) in the phytase-treated groups, with the T 2 group (1000 FTU) demonstrating superior performance compared to the non-supplemented control. On the other hand, phytase supplementation improved leg quarter yield but had no effect on overall carcass yield or breast weight, according to Scheideler and Ferket (2000) [16] . Similarly, Pillai et al. (2006) [13] observed that the inclusion of fungal phytase at 600 FTU/kg in a low-phosphorus diet resulted in carcass yield, breast and thigh weights comparable to those in the normal phosphorus control group. Supporting these findings, Juncqueira et al. (2011) [3] reported that supplementing low-phosphorus diets with 750 and 1000 FTU/kg of phytase did not significantly affect carcass yield; however, leg and thigh weights were lower than the control group, while breast weight showed some improvement. More recently, Prabhuraja et al. (2024) [14] noted no significant differences (p>0.05) in carcass characteristics including dressing percentage, thigh yield, breast and drumstick, abdominal fat content and weights of internal organs such as the heart, liver, proventriculus and gizzard between the control and phytase-supplemented lowphosphorus groups, as well as among the various phytasesupplemented groups.

Conclusion

This study demonstrated that incorporating high levels of phytase (2500 FTU) into a low-phosphorus diet offers greater benefits compared to the standard phytase inclusion level (500 FTU) in broiler nutrition. The results suggest that super dosing phytase in phosphorus-deficient diets positively influences both body weight and carcass yield in broiler chickens.

Acknowledgement

AcknowledgmentThe financial support received from Department of Biotechnology; Government of India is thankfully acknowledged.

References

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