Objectives: This experiment evaluated the effect of phytase super dosing on performance, tibia bone quality and serum biochemistry of broiler chicken. Materials and Methods: A total of 96 day-old chicks were distributed randomly into four treatment groups: D0, D1, D2, D3 with four replicates per treatment (6 chicks per replicate). The treatments were control diet (D0), control diet +500 FTU phytase kg1 (D1), control diet +1500 FTU phytase kg1 (D2) and control diet +2500 FTU phytase kg1 (D3), that were fed to the birds from day 13-28. Birds were offered a commercial starter diet from day 0-12. Results: The different levels of phytase had no significant effect on body weight gain (BWG) and feed intake (FI). Supplementation of 1500 FTU phytase kg1 of diet showed better (p<0.05) FCR than those received 2500 FTU phytase kg1 of diet. Diet with 1500 FTU phytase kg1 increased (p<0.05) the serum concentration of phosphorus (P) and total protein (TP). Inclusion of 1500 FTU phytase kg1 of diet increased (p<0.05) the calcium (Ca) content of tibia. Diets supplemented with 500 and 1500 FTU phytase kg1 reduced (p<0.05) the heart weight but increased (p<0.05) the drumstick weight of birds. Supplementation of 500 and 1500 FTU phytase kg1 diet significantly reduced the total feed cost, production cost and increased the total profit kg1 live bird. Conclusion: Supplementing diets with 500 and 1500 FTU phytase kg1 improved the overall production performance of broiler chickens and consequently enhanced economic profitability.
S. Hossain, M.A. Hossain, N. Akter and M. Akter, 2022. Effects of Phytase Super Dosing on Performance, Plasma Mineral Contents and Bone Mineralization in Broiler Chicken. International Journal of Poultry Science, 21: 1-9.
The plant-based poultry diet contains an important antinutrient factor called phytate (IP6) which is the major storage site of phosphorus (P). Phytate not only limits the availability of phosphorus (P) but also other minerals and nutrients like protein, carbohydrate, etc1. Poultry is unable to hydrolyze phytate due to a lack of effective endogenous phytase activity2. Moreover, the endogenous intestinal phytase poorly hydrolyzes the phytate due to the different pH levels and cation concentrations of the gastrointestinal tract (GIT) of poultry3. Therefore, exogenous phytase is routinely added to the poultry diet to improve the availability of phytate-bound minerals and nutrients. A significant amount of literature has already reported the beneficial effect of conventional dose of phytase (500 FTU kg1) on growth performance, nutrient utilization and bone quality of broiler chickens1,4-7.
The corn-soybean-based poultry diet contains around 28% phytate which stores 60-80% of the total P8. It has been reported that 500 FTU kg1 of phytase could only hydrolyze 62% of the total phytate and released only 0.15% phytate-P9. Due to several extrinsic and intrinsic factors, the conventional dose (500 FTU kg1) of phytase cannot completely dephosphorylate the phytate10. Increasing the phytase level by more than 500 FTU kg1 of diet could potentially maximize the phytase-induced benefits in poultry.
Phytase causes stepwise hydrolysis of dietary phytate (IP6) and produces intermediate esters (like IP5, IP4, IP3, IP2 and IP1) of inositol. Commercial or standard phytase dose breakdown the phytate (IP6) and subsequently releases IP4 and IP3 esters which are more soluble and suspectable to phytase-induced digestion than IP6 and IP5. As broiler lacks endogenous phytase, the concentration of these intermediate esters increases in the intestine unless an increased dose of exogenous phytase is added to the diet11,12. Previous study claimed that higher dose of phytase (1500 FTU phytase kg1 of diet) could potentially hydrolyze the IP4 and IP3 and thereby ameliorate their anti-nutritive effect completely through the production of free inositol which subsequently plays an important role in improving the performance of broiler chickens13.
The first work of phytase super-dosing was reported by Nelson et al.14 where the effect of phytase super dose (950-7600 FTU kg1) was evaluated. The authors observed that the phytate-P disappearance increased by 55.5% when the phytase dose increased from 950-7600 FTU kg1. The weight gain and ash content of bone at 21 day were highest at 7,600 FTU kg1 of diet14. Another study stated that supplementation of phytase between 1000 FTU kg1 and 5000 FTU kg1 of diet significantly improved length, width and mineral content of tibia bone compared to a diet with 500 FTU kg1 of phytase15. According to Shirley and Edwards16 supplementation of 12000 FTU phytase kg1 of the diet effectively hydrolyzed 95% of phytate-P. This enhanced efficacy of phytase super dosing could be due to the complete hydrolysis of phytate and release of minerals (P, Ca, Zn, Fe, etc.) and other nutrients, like protein and energy17,18.
Most of the studies stated that the benefits of phytase super dosing become more pronounce when supplemented to non-phytate P (NPP) deficient diet2,15,19-22. Although these studies reported the positive effect, the impact of phytase super dosing is still inconsistent as the phytase dose and NPP level of the diet varied over the literature. Moreover, the amount of literature on phytase super dosing is very limited in the Bangladesh context. Therefore, the present study was undertaken to evaluate the effect of phytase super dosing on the performance, bone quality and serum profile of broiler chickens.
MATERIALS AND METHODS
Study site and Ethical approval: The experiment was carried out at the Department of Dairy and Poultry Science, Chattogram Veterinary and Animal Sciences University (CVASU). The experimental procedures were approved by CVASU Ethics Committee (EC) and the EC Approval No. is CVASU/Dir(R&E) EC/2019/94(7).
Formulation of experimental diets: The birds were fed a commercial (Nahar TM) broiler starter diet (Table 1) up to 12 days of age. After that, experimental diets were prepared and fed the birds from day 13-28. Four different test diets (D0, D1, D2 and D3) were formulated with the locally available feed ingredients to fulfill or exceed the requirements of NRC23 where diets were iso-caloric and iso-nitrogenous.
All feedstuffs were used to formulate a control diet without phytase (D0), whereas D1, D2 and D3 experimental diets were prepared with the supplementation of phytase at the rate of 500 FTU, 1500 FTU and 2500 FTU, respectively. Phytase (Renaphytase®) was purchased from Renata Pharmaceuticals Ltd. The mineral matrix value of phytase (Ca = 80%, avP = 92%) were considered during formulation of experimental diets. The composition and nutritive values of formulated finisher test diets are shown in Table 2 and 3, respectively.
Management of birds: A total of 96 Cobb-500 day-old broiler chicks of both sexes were purchased from the local hatchery. The chicks were weighed on receiving day and then randomly assigned into four dietary treatment groups (D0, D1, D2 and D3), where each treatment was replicated 4 times with 6 birds per replicate in a completely randomized design (CRD). The birds were allocated to 16 equal-sized, clean and disinfected cages which were furnished with feeders and drinkers. Each pen (4.4 sq. ft.) was allotted for 6 birds. Therefore, floor space for each bird was 0.73 sq. ft. The birds were exposed to a temperature of 35°C for the first two days. Then the temperature was gradually reduced by 1 or 2°C after every 1 or 2 days until the chicks arrived at 10 days of age. Afterward, the poultry shed temperature was maintained at 25°C for the rest of the trial. All the birds had free access to diets and fresh, clean and cool drinking water during the entire trial period. Other standard management and vaccination programs were maintained according to the breeder manual.
Sample collection: On day 28, two birds were selected randomly from each replicate for sample collection. The birds were slaughtered humanely by cutting the jugular vein. Blood samples were collected in a falcon tube separately. After centrifugation at 5000 revolutions per minute, the serum samples were taken into the 2ml Eppendorf tube and stored at -20ºC until further analysis. The tibia bones were also collected from the same birds and stored at -20ºC for further processing and analysis. Different meat yield parameters such as carcass weight, dressed weight, weights of different meat cuts (neck, thigh, wings, breast, drumstick) and giblets weights (heart, lungs, liver, shank, proventriculus and gizzard and abdominal fat) were recorded. Besides, weights of other samples such as small intestine, pancreas, proventriculus, meat yields and cuts were also recorded from the same birds to evaluate carcass yields. Bodyweight, feed intake and remaining feeds were recorded weekly basis and the FCR was calculated accordingly. As there was no occurrence of death in the bird population during the trial period, so mortality was not recorded.
Sample processing and analyses: Feed samples were collected from formulated test diets before feeding the birds. The samples were processed by grinding with the help of mortar and pestle and then mixed thoroughly for lab analyses. About 500 g of each diet of finisher were taken for proximate analysis. The samples were tested for proximate analysis having dry matter (DM%), moisture%, crude protein (CP%), Crude Fiber (CF%) and ash using standard laboratory procedures24. Dry matter estimation was done by the oven-dry method. Crude protein estimation was accomplished by the Kjeldahl Method. Ash was measured by igniting the pre-ashing sample on a muffle furnace at a temperature of 600°C for four to six hours. The serum total protein (TP), Calcium (Ca), Phosphorus (P), alkaline phosphatase (AP), GPT (glutamic pyruvic transaminase), GOT (glutamic oxaloacetic transaminase) levels were analyzed by using their respective standard assay kit (Randox Laboratories Ltd, UK) and semi-automated Humalyzer (Humalyzer 4000 Merck®, Germany).
Bone Sample: The left tibia from each sampled bird was collected and weighed. Length and width were also measured for each tibia after removing the flesh. The Seedor index (the ratio of bone weight and length) was also calculated. The seedor index was calculated by dividing the bone weight (mg) by its length (mm)2,25. The tibia bones were dried in a force draft oven (95°C) to reach a constant weight. The dried tibia bones were ashed at 650°C for 23 h. The samples were processed by grinding with the help of mortar and pestle and then mixed thoroughly. The bone ash for each tibia was then analyzed for Ca and P content using standard laboratory procedures26.
Production cost: Cost of production was calculated considering the expense on chick, feed, medicine, labor, etc. Chick cost was calculated from the purchasing cost. Feed cost was considered from the sale price of the feed marketed through dealers.
Statistical analysis: All collected data were analyzed using one-way analysis of variance (ANOVA)followed by least significance difference (LSD) test using the SPSS software V.25 (SPSS, Inc., IBM, Chicago, Illinois, USA). Statistical significance was considered at p≤0.05.
Gross responses: The effect of the increased level of phytase supplementation on gross responses of broiler chickens is summarized in Table 4. There was no effect (p>0.05) of phytase on BWG and FI of broiler chickens from day 13-28. However, the highest weight gain was recorded for the diet supplemented with 1500 FTU phytase kg1. The FCR of broilers was significantly influenced by dietary treatment from day 13-28. Supplementation of 1500 FTU phytase kg1 of diet showed better (p<0.05) FCR compared to the birds that received diets containing 2500 phytase kg1.
Tibia bone development: The effect of phytase supplementation on tibia bone development of broiler chickens is summarized in Table 5. There was no effect (p>0.05) of phytase inclusion on the weight of the tibia bone of broiler chickens from day 13-28. However, the length and width of the tibia bone were significantly influenced by phytase supplementation. Addition of 2500 FTU phytase kg1 of diet reduced (p<0.001) the length and width of the tibia bone of broiler chickens. Birds supplemented 500 FTU phytase kg1 of diet showed the highest (p<0.001) SI of the tibia bone. Diet supplemented with 1500 FTU phytase kg1 of the diet increased (p<0.002) the Ca content of tibia bone compared to other diets. Supplementation of phytase did not affect (p>0.05) the P concentration of tibia bone of broiler chickens.
Serum biochemistry: The effect of phytase supplementation on serum contents of broiler chickens from day 13-28 is summarized in Table 6. Supplementation of 500 and 1500 FTU phytase kg1 of the diet increased p<0.001) the serum TP and P levels of birds compared to those fed diets with 0 and 2500 FTU phytase kg1. Phytase supplementation had no significant effect on serum Ca, GPT and GOT levels in broiler chickens.
Carcass yield parameters: The effect of phytase supplementation on carcass yield and cuts of broiler chickens is summarized in Table 7. There was no significant effect of phytase supplementation on dressing percent and meat yields except for drumstick. Diet supplemented with 500 and 1500 FTU phytase kg1 had bigger (p<0.05) drumsticks than those on diets containing 0 and 2500 FTU phytase kg1.