Phosphorus utilization in finishing broiler chickens: effects of dietary calcium and microbial phytase

Efficacy and Equivalency of Phytase for Available Phosphorus in Broilers Fed an Available Phosphorus-Deficient Diet

This study was conducted to assess the effectiveness of phytase on the performance, carcass traits, nutrient digestibility, tibia characteristics, and inositol phosphorus (IP) degradation in broiler chickens. Additionally, the available phosphorus (AP) equivalency of phytase in AP-deficient diets was estimated for 35 days after hatching. A total of 336 one-day-old Ross 308 broiler chicks were allocated to one of seven dietary treatments with six replications with eight birds per cage. The dietary treatments were as follows: (1) positive control containing 0.45% AP of the starter and 0.42% AP of the grower diet (PC), (2) 0.10% AP deficiency from the PC (NC-1), (3) 0.15% AP deficiency from the PC (NC-2), (4) 0.20% AP deficiency from the PC (NC-3), (5) NC-3 +phytase (500 FTU/kg; NC-3-500), (6) NC-3 + phytase (1000 FTU/kg; NC-3-1000), and (7) NC-3 + phytase (1500 FTU/kg; NC-3-1500). On d 35, the NC-3 diet exhibited lower tibia weight compared to the other treatments (p < 0.001). The NC-3-1500 group had higher calcium and phosphorus contents in the tibia than the other treatments on d 35 (p < 0.01). Phytase supplementation led to a reduced IP6 concentration and increased IP3 concentrations in different sections of the gastrointestinal tract on d 21 and 35 compared to the control diet (p < 0.05). In conclusion, based on the tibia phosphorus content, this study determined that 500 FTU/kg phytase was equivalent to 0.377% and 0.383% AP in the diet on d 21, and 0.317% and 0.307% AP in the diet on d 35, respectively. Likewise, 1000 FTU/kg was determined to be equivalent to 0.476% and 0.448% AP on d 21, and 0.437% and 0.403% AP on d 35, respectively. Furthermore, 1500 FTU/kg was determined to be equivalent to 0.574% and 0.504% AP on d 21, and 0.557% and 0.500 AP on d 35, respectively.

A first model of the fate of dietary calcium and phosphorus in broiler chickens

To reduce P excretion and increase the sustainability of poultry farms, one needs to understand the mechanisms surrounding P metabolism and its close link with Ca metabolism to precisely predict the fate of dietary P and Ca and related requirements for birds. This study describes and evaluates a model developed to estimate the fate of Ca and P consumed by broilers. The Ca and P model relies on three modules: (1) digestion of Ca and P; (2) dynamics of Ca and P in soft tissue and feathers; and (3) dynamics of body ash. Exogenous phytase affects the availability of Ca and P; thus, to predict the absorption of those minerals, the model also accounts for the effect of phytase on Ca and P digestibility. We used a database to estimate the consequences of dietary Ca, P, and phytase over feed intake response. This study followed a four-step process: (1) Ca and P model development and its coupling with a growth broiler model; (2) model behavior assessment; (3) sensitivity analysis to identify the most influential parameters; and (4) external evaluation based on three databases. The proportion of P in body protein and the Ca to P ratio in bone are the most sensitive parameters of P deposition in soft tissue and bone, representing 91 and 99% of the total variation. The external evaluation results indicated that body water and protein had an overall mean square prediction error (rMSPE) of 7.22 and 12.3%, respectively. The prediction of body ash, Ca, and P had an rMSPE of 7.74, 11.0, and 6.56%, respectively, mostly errors of disturbances (72.5, 51.6, and 90.7%, respectively). The rMSPE for P balance was 13.3, 18.4, and 22.8%, respectively, for P retention, excretion, and retention coefficient, with respective errors due to disturbances of 69.1, 99.9, and 51.3%. We demonstrated a mechanistic model approach to predict the dietary effects of Ca and P on broiler chicken responses with low error, including detailed simulations to show the confidence level expected from the model outputs. Overall, this model predicts broilers' response to dietary Ca and P. The model could aid calculations to minimize P excretion and reduce the impact of broiler production on the environment. A model inversion is ongoing that will enable the calculation of Ca and P dietary quantities for a specific objective. This will simplify the use of the model and the feed formulation process.

Approaches to determine the efficiency of novel 3-phytase from Klebsiella pneumoniae and commercial phytase in broilers from 1 to 14 d of age

This study aimed to evaluate the effects of a laboratory 3-phytase (the expression of the phyK gene, Lab-Phy) and a commercial 6-phytase (Quantum Blue 40 P, Com-Phy) alone and in combination (corn-soy-based diets) in broilers. A total of 400, day-old Ross 308 male broilers were randomly assigned to 5 treatments with 10 replicate cages (8 chicks/cage) for a 14-day trial. Experimental treatments included the positive control (0.95% Ca and 0.48% nonphytate phosphorus (nPP), PC), negative control (0.90% Ca and 0.22% nPP, NC), and NC which was supplemented with Lab-Phy 250 FTU/kg and Com-Phy 250 FTU/kg alone or in combination of Lab-Phy 125 FTU/kg and Com-Phy 125 FTU/kg. The inclusion of Lab-Phy in the NC diet significantly improved the P and Ca content in the tibia compared to the NC group. Moreover, the inclusion of Com-Phy alone and in combination with Lab-Phy in the NC diet significantly increased the P and Ca content in the tibia compared to the Lab-Phy. The mRNA expression of NaPi-IIb was upregulated in the duodenum by the reduction of nPP and downregulated by the inclusion of any phytase, whereas other nutrient transporters were not influenced by the reduction of nPP or the addition of phytase in the small intestine mucosa. Broilers receiving the NC diet obtained the lowest body weight (BW) and body weight gain (BWG) at 8 to 14 and 1 to 14 d of age. The NC group showed the lowest villi height and surface area, Newcastle disease (ND) antibody titer, and digestibility of nutrients compared to the PC group at 14 d of age. Supplementing the NC diet with the Lab-Phy and Com-Phy individually, or in combination tended to improve BW, BWG, tibia characteristics, villi characteristics, ND, and retained CP and P, and apparent ileal digestibility of CP, P, methionine, and threonine. The present research indicated that the studied traits by the combination of phytases were slightly better than the average of the 2 individually, suggesting there might be some value in combining the laboratory and commercial phytases.

Nutritional and Functional Roles of Phytase and Xylanase Enhancing the Intestinal Health and Growth of Nursery Pigs and Broiler Chickens

This review paper discussed the nutritional and functional roles of phytase and xylanase enhancing the intestinal and growth of nursery pigs and broiler chickens. There are different feed enzymes that are currently supplemented to feeds for nursery pigs and broiler chickens. Phytase and xylanase have been extensively studied showing consistent results especially related to enhancement of nutrient digestibility and growth performance of nursery pigs and broiler chickens. Findings from recent studies raise the hypothesis that phytase and xylanase could play functional roles beyond increasing nutrient digestibility, but also enhancing the intestinal health and positively modulating the intestinal microbiota of nursery pigs and broiler chickens. In conclusion, the supplementation of phytase and xylanase for nursery pigs and broiler chickens reaffirmed the benefits related to enhancement of nutrient digestibility and growth performance, whilst also playing functional roles benefiting the intestinal microbiota and reducing the intestinal oxidative damages. As a result, it could contribute to a reduction in the feed costs by allowing the use of a wider range of feedstuffs without compromising the optimal performance of the animals, as well as the environmental concerns associated with a poor hydrolysis of antinutritional factors present in the diets for swine and poultry.

Effects of dietary calcium and phosphorus restrictions on growth performance, intestinal morphology, nutrient retention, and tibia characteristics in broiler chickens

1. This study evaluated the effects of dietary calcium (Ca)‎ and available phosphorus (aP) restrictions on growth performance, intestinal morphology, nutrient apparent total tract retention (ATTR), and tibia characteristics.2. A total of 1296, one-day-old male Ross-308 broilers were reared for 42 d. During the ‎starter phase (1-10 d), all birds were fed a nutrient-adequate diet (C). Diets fed during the grower phase (11-24 d) included: 1. C; 2. 15% of the Ca and aP in C; 3. 30% of the Ca and aP in C. At the beginning of the finisher phase (25 d), chickens fed the C diet were divided into two subgroups including C, and C+ phytase (500 FTU/kg). Restricted treatments were divided into eight subgroups as 1. C; 2. 10% of the Ca and aP in C; 3. 20% of the Ca and aP in C; 4. 30% of the Ca and aP in C; 5. C+ phytase; 6. 10% of the Ca and aP in C+ phytase; 7. 20% of the Ca and aP in C+ phytase and 8. 30% of the Ca and aP in C+ phytase.3. On d 24 and 42, ATTR of Ca and phytate phosphorus (pP) were linearly increased by decreasing Ca and aP levels (P<0.05). Birds receiving phytase showed higher nutrient ATTR ‎compared to those fed non-phytase supplemented diets (P<0.05). Tibia Ca and P were linearly decreased at 24 d (P<0.05) and tibial ash was linearly decreased (P<0.05) at 42 d by decreasing levels of Ca and aP in finisher diets (without phytase)‎. By decreasing the levels of Ca and aP in the finisher diets (with phytase) with a 30% reduction of Ca and aP in the grower phase, tibia ash linearly decreased (P <0.05). Using 500 FTU/kg phytase improved tibia traits compared to non-phytase supplemented treatments (P<0.05).4. In general, decreasing dietary Ca and aP (up to 30%) during grower and finisher phases increased ATTR of minerals and decreased Ca, P and breaking strength (BS) of tibia without any negative effect on growth performance or intestinal morphology. Reduced dietary Ca and aP decreased tibial ash content, although 500 FTU/kg phytase improved ATTR of minerals and tibia attributes.

Determination of the standardized ileal digestible calcium requirement of male Arbor Acres Plus broilers from day 25 to 42 post-hatch

An experiment was conducted to determine the standardized ileal digestible (SID) Ca requirement of Arbor Acres Plus male broilers from d 25 to 42 post-hatch. Broilers were obtained at hatch, placed in floor pens, and fed a nutrient adequate diet until d 24 post-hatch. On d 25, twelve hundred birds were weighed and allocated to one of 4 treatments. There were 25 birds per pen and 12 pens per diet. The diets were formulated to contain 0.46, 0.35, 0.24, or 0.13% SID Ca. Available P (avP) was 0.39% in all diets, including 0.16% avP expected from 2,500 FYT/kg of phytase. The SID Ca requirement was estimated using nonlinear models, including quadratic, straight broken-line, and quadratic broken-line. There was no effect of SID Ca on feed intake, body weight gain, feed conversion ratio, or livability. Tibia ash percent was greatest in birds fed 0.35% SID Ca and lowest in birds fed 0.13% SID Ca (quadratic, P = 0.063). Apparent ileal digestibility (AID) of Ca was highest in birds fed the diets containing 0.13% SID Ca and decreased (quadratic, P = 0.014) as dietary SID Ca increased to 0.46%. Apparent digested Ca was highest in birds fed 0.35% SID Ca and lowest in birds fed 0.13% SID Ca (quadratic, P = 0.005). Decreasing the concentration of SID Ca in the diet from 0.46 to 0.13% (P < 0.0001) increased the AID of P and apparent digested P. Litter N or P were lowest in birds fed 0.35% SID Ca and increased (quadratic, P ≤ 0.05) as dietary SID Ca decreased to 0.13%. Non-linear equations, developed using tibia ash percent, digested Ca, or litter P, estimate the SID Ca requirement of Arbor Acres Plus broilers from d 25 to 42 was 0.37, 0.35, or 0.35%, respectively. This corresponds to an SID Ca to available P ratio of 0.95 to 0.90.

Growth performance, carcass and meat quality, bone strength, and immune response of broilers fed low-calcium diets supplemented with marine mineral complex and phytase

Influence of marine mineral complex (CeltiCal) as a partial substitute for limestone on growth efficiency, carcass traits, meat quality, bone strength, calcium (Ca) retention, and immune response was investigated in broilers fed low-Ca diets with or without phytase (PHY) addition for a 35-d trial period. A total of 300 one-day-old Ross 308 straight-run broilers were randomly allocated to: T1 (positive control), recommended Ca levels + PHY; T2 (negative control), 0.2% below the recommended Ca levels + PHY; T3, 0.1% below the recommended Ca levels + 0.2% CeltiCal + PHY; T4, 0.2% below the recommended Ca levels + 0.4% CeltiCal + PHY; T5, 0.2% below the recommended Ca levels + 0.4% CeltiCal. PHY was added at 500 phytase units/kg diets. Each dietary treatment had 10 replications of 6 chicks each. Results revealed that production efficiency factor was greater for T4 compared to T2 and T5 during 22-35 d and for T1, T3, and T4 compared to T2 during 0 to 35 d (P < 0.05). Feed conversion ratio was lower for T3 and T4 compared to T2 and T5 during 0 to 35 d (P < 0.05). T4 had a greater (P < 0.05) dressing percentage than T2, which had a lighter (P < 0.01) small intestinal relative weight than all other treatments. Breast meat temperature at 15 min postmortem was highest for T1 and lowest for T3 (P < 0.001). Breast meat pH was greater for T1 compared to T5 at 15 min postmortem and for T3 compared to T4 at 24 h postmortem (P < 0.05). T5 had a lower breast meat redness than all other treatments at 15 min postmortem and then T1 and T3 at 24 h postmortem (P < 0.01). Tibia and femur weights were greater (P < 0.05) for T3, T4, and T5 compared to T2, which had the lowest tibia ash content (P < 0.05) and femur geometric properties (P < 0.001). Greater antibodies to infectious bronchitis virus (P < 0.01) and Ca retention (P < 0.001) were observed for T3 and T4 in comparison to T2. Based on the findings of this research, CeltiCal can adequately replace a considerable portion of limestone in broiler reduced-Ca diets containing PHY.

How do pigs deal with dietary phosphorus deficiency?

Feeding strategies for growing monogastric livestock (particularly pigs) must focus on maximising animal performance, while attempting to reduce environmental P load. Achieving these goals requires a comprehensive understanding of how different P feeding strategies affect animal responses and an ability to predict P retention. Although along with Ca, P is the most researched macromineral in pig nutrition, knowledge gaps still exist in relation to: (1) the effects of P feed content on feed intake (FI); (2) the impact of P intake on body composition; (3) the distribution of absorbed P to pools within the body. Here, we address these knowledge gaps by gathering empirical evidence on the effects of P-deficient feeds and by developing a predictive, mechanistic model of P utilisation and retention incorporating this evidence. Based on our statistical analyses of published literature data, we found: (1) no change in FI response in pigs given lower P feed contents; (2) the body ash–protein relationship to be dependent upon feed composition, with the isometric relationship only holding for pigs given balanced feeds and (3) the priority to be given towards P retention in soft tissue over P retention in bones. Subsequent results of the mechanistic model of P retention indicated that a potential reduction in P feeding recommendations could be possible without compromising average daily gain; however, such a reduction would impact P deposition in bones. Our study enhances our current knowledge of P utilisation and by extension excretion and could contribute towards developing more accurate P feeding guidelines.

A reassessment of the vitamin D requirements of modern broiler genotypes

We hypothesized that performance and bone mineralization of 2 broiler lines will benefit from increasing vitamin D (vitD) supplementation above current commercial levels and by partial substitution of D3 by 25-OH-D3. Male Ross 308 and 708 chicks (n = 576), were offered diets with low (LD; 1,000), medium (MD; 4,000) or high levels of D3 (HD; 7,000 IU/kg), and medium levels of vitD where the majority of D3 was substituted by 25-OH-D3 (25MD; 1,000 D3+3,000 25-OH-D3 IU/kg). Performance was measured at the end of starter (day 10), grower (day 24), and finisher periods (day 38). Three birds per pen were dissected at the end of each period to assess tibia and femur ash percentage (%), ash weight, bone breaking strength (BBS), and serum levels of 25-OH-D3. Remaining birds were gait scored (GS) at day 37 of age. Genotype and diet did not interact for any trait, whilst performance was not affected by diet. Ross 708 had lower body weight (P < 0.005), higher feed conversion ratio over the grower period (P < 0.05), similar levels of 25-OH-D3, but higher GS (P < 0.05) than Ross 308. Serum 25-OH-D3 levels were affected by diet at the end of the starter and grower periods (P < 0.05), being lowest for LD and highest for 25MD. Diet affected GS (P < 0.01), being higher in LD than 25MD. Femur ash % was higher at the end of the starter and grower periods for 25MD than LD and for both HD and 25MD than LD (P < 0.05). Femur and tibia ash weight were higher for 25MD in comparison to LD birds (P < 0.05) at the end of the grower period. Femur and tibia BBS were higher (P < 0.05) for 25MD in comparison to LD at the end of the grower and finisher periods, respectively. Overall, effects of vitD supply were more pronounced for femur than for tibia mineralization. Results do not suggest supplementation of vitD above current maximum levels and support partial substitution by 25-OH-D3.

High stocking density alters bone-related calcium and phosphorus metabolism by changing intestinal absorption in broiler chickens

Live performance, bone health and metabolic responses to the interaction among stocking density and dietary concentrations of total calcium (TCa) and non-phytate phosphorus (NPP) were determined on 2,232 Ross 308 female broilers over a 3-wk experimental period. From 22 d of age, birds were randomly divided into 48 groups and provided with different corn-soybean meal-based diets varying in TCa (0.70% or 0.90%) and NPP (0.28% or 0.36%) content at 1 of 2 stocking densities [28.6 (LSD, 13 broilers/m2) and 39.6 (HSD, 18 broilers/m2) kg of predicted final BW/m2 floor space], according to a 2 × 2 × 2 factorial design with 6 replications in each treatment. Regardless of NPP supplementation, a high-TCa (0.90%) diet aggravated the impact of HSD on growth (BW gain and feed efficiency, P < 0.001) and motility (gait score, P < 0.001). This might be explained by deteriorating tibia quality (relative weight, mineral composition and biomechanical property; P < 0.01), due to the involvement of decreasing duodenal absorption (type IIb sodium-phosphate co-transporter mRNA, P < 0.001) in reduced phosphorus retention (P < 0.001). On the contrary, increasing dietary NPP (0.36%), particularly if high in TCa (0.90%), boosted TCa retention (P < 0.05) by improving absorption (calcium-binding protein D28k transcription, P < 0.05) for LSD chickens, hence enhancing bone development (relative tibia weight and tibia breaking strength, P < 0.05) and leg health (walking ability, P < 0.05). Together, HSD and LSD birds show an impaired TCa tolerance and a higher TCa+NPP threshold, respectively, to allow the optimization of bone quality via altered intestinal absorption.

Tibia mineralization of chickens determined to meat production using a microbial phytase

The target of the research was 6-phytase of microbial origin. It was used in feed mixtures for chickens determined to meat production. Its effect has been studied in relation to the tibia mineralization by calcium, phosphorus and magnesium. 6-phytase is a product of Aspergillus oryzae. That was obtained by means of biotechnological processes of production of commercially available enzymes. It was incorporated in the feed mixtures 0.1%. In a 38-day feeding trial, 300 one-day-old, as hatched, Cobb 500 chickens determined to meat production (100 birds per group) were fed on one concentrations of dietary non-phytate phosphorus (2.32, 2.31 g.kg-1, respectively and supplemental microbial phytase (0 and 500   FTU.kg-1 feed mixtures). Control group was used to compare the results and control feed mixtures contained 4.5 g.kg-1 without microbial phytase. At days 40 it was selected 6 birds in every group, which were slaughter in accordance with the principles of welfare. Left tibias of every bird were used to determination of calcium, phosphorus and magnesium contents. According to in vivo, it was found that the addition of microbial phytase to reduced dietary non-phytate phosphorus increased concentrations of calcium (Ca), phosphorus (P) and magnesium (Mg) in tibia. The differences among groups were statistically significant (p <0.05). It was concluded that reducing of dietary non-phytate phosphorus on the 2.32, 2.31 g.kg-1, respectively, by monocalcium phosphate and microbial phytase supplementation in feed mixtures facilitated tibia mineralization at chicken determined to meat production.

Effect of dietary calcium concentrations in low non-phytate phosphorus diets containing phytase on growth performance, bone mineralization, litter quality, and footpad dermatitis incidence in growing broiler chickens

Objective

An experiment was conducted to investigate the effect of dietary Ca concentrations in low non-phytate phosphorus (NPP) diets containing phytase on growth performance, bone mineralization, litter quality, and footpad dermatitis (FPD) incidence in growing broiler chickens.

Methods

A total of 1,800 21-day-old Ross 308 growing broiler chickens were allotted to 1 of 6 dietary treatments with 6 replicated cages. Six diets were formulated to provide increasing Ca concentrations of 4.0, 5.0, 6.0, 7.0, 8.0, or 9.0 g/kg in diets. The concentrations of NPP in all diets were maintained at 3.0 g/kg, and phytase was supplemented to all diets at the level of 1,000 fytase units (FTU)/kg. At the end of the 14-d feeding trial, birds were euthanized for tibia sampling, and litter samples were collected from 3 areas in the cage. The FPD incidence was measured based on a 6-point scoring system.

Results

Dietary Ca concentrations had no effect on growth performance of growing broiler chickens. However, a tendency (linear, p = 0.05) for decreased feed efficiency was observed as dietary Ca concentrations were increased. The concentrations of Ca and P in the tibia of broiler chickens increased (linear and quadratic, p<0.01) with increasing Ca concentrations in low NPP diets containing phytase. Litter pH, moisture, and N contents were not affected by increasing Ca concentrations in low NPP diets containing phytase. However, a tendency (quadratic, p = 0.10) for increased FPD incidence with increasing dietary Ca concentrations was observed.

Conclusion

Dietary Ca concentrations from 4.0 to 9.0 g/kg in low NPP diets containing phytase have little effects on growth performance of growing broiler chickens. However, Ca and P concentrations in the tibia are decreased if dietary Ca concentrations are less than 5.0 g/kg. The FPD incidence for growing broiler chickens may be decreased if less than 9.0 g/kg of Ca is included in diets.

Adaptive response of broilers to dietary phosphorus and calcium restrictions

The aim of this study was to evaluate the capacity of chickens to adapt to and compensate for early dietary restriction of non-phytate P ( NPP: ) and/or Ca (10 to 21 d) in a later phase (22 to 35 d), and to determine whether compensatory processes depend on the P and Ca concentrations in the finisher diet. Four diets were formulated and fed to broilers from 10 to 21 d in order to generate birds with different mineral status: L₁ (0.6% Ca, 0.30% NPP), L₂ (0.6% Ca, 0.45% NPP), H₁ (1.0% Ca, 0.30% NPP), and H₂ (1.0% Ca, 0.45% NPP). On d 22, each group was divided into three groups which received a low (L, 0.48% Ca, 0.24% NPP), moderate (M, 0.70% Ca, 0.35% NPP), or high (H, 0.90% Ca, 0.35% NPP) finisher diet until 35 d, resulting in a total of 12 treatments. Lowering the Ca level enhanced apparent ileal digestibility of P (P AID) at 21 d especially with the high NPP level (Ca × NPP, P < 0.01). The lower bone mineralization observed at 21 d in broilers fed the L₁ diet compared to those fed the H₂ diet had disappeared by 35 d with long-term stimulation of the P AID with the low NPP level (P < 0.001). Although P AID and growth performance were improved in birds fed the L₁L compared to the L₁H and H₂H treatments, tibia characteristics tended to be lower in birds fed the L₁L compared to those fed the L₁H treatment. Birds fed the H₁M treatment had higher P AID, growth performance and tibia ash content than those fed the H₁H treatment. A significant increase in the mRNA levels of several genes encoding Ca and P transporters was observed at 35 d in birds fed the L₁ followed by the L diet compared to birds fed the L₁ followed by the M diet. In conclusion, chickens are able to adapt to early dietary changes in P and Ca through improvement of digestive efficiency in a later phase, and the extent of the compensation in terms of growth performance and bone mineralization depends on the P and Ca levels in the subsequent diet.

Effect of super dosing of phytase on growth performance, ileal digestibility and bone characteristics in broilers fed corn-soya-based diets

A feeding trial was designed to assess the effect of super dosing of phytase in corn-soya-based diets of broiler chicken. One hundred and sixty-eight day-old broilers were selected and randomly allocated to four dietary treatment groups, with 6 replicates having 7 chicks per treatment group. Two-phased diets were used. The starter and finisher diet was fed from 0 to 3 weeks and 4 to 5 weeks of age respectively. The dietary treatments were consisted of normal phosphorus (NP) group without any phytase enzyme (4.5 g/kg available/non-phytin phosphorus (P) during starter and 4.0 g/kg during finisher phase), three low-phosphorus (LP) groups (3.2 g/kg available/non-phytin P during starter and 2.8 g/kg during finisher phase) supplemented with phytase at 500, 2500, 5000 FTU/kg diet, respectively, to full fill their phosphorus requirements. The results showed that super doses of phytase (at 2500 FTU and 5000 FTU/kg) on low-phosphorus diet improved feed intake, body weight gain, ileal digestibility (serine, aspartic acid, calcium, phosphorus), blood P levels and bone minerals such as calcium (Ca), P, magnesium (Mg) and zinc (Zn) content. It could be concluded that super doses of phytase in low-phosphorus diet were beneficial than the normal standard dose (at 500 FTU/kg) of phytase in diet of broiler chicken.

Effect of calcium level and phytase addition on ileal phytate degradation and amino acid digestibility of broilers fed corn-based diets

This study investigated the effect of dietary Ca to available P (AvP) ratio and phytase supplementation on bone ash, ileal phytate degradation, and nutrient digestibility in broilers fed corn-based diets. The experimental design was a 4 × 2 factorial arrangement of treatments evaluating 4 Ca:AvP ratios (1.43, 2.14, 2.86, and 3.57) and 2 levels of phytase (0 and 1,000 phytase units/kg of feed). The 4 Ca:AvP ratios were achieved by formulating all diets to a constant AvP level of 0.28% and varying Ca levels (0.4, 0.6, 0.8, and 1.0%). Each treatment was fed to 6 cages of 8 male Ross 308 broilers from 5 to 21 d. At 21 d, digesta from the terminal ileum was collected and analyzed for energy, phytate, P, Ca, and amino acids (AA) to determine digestibility. Digesta pH was measured in each segment (crop, gizzard, duodenum, and ileum) of the digestive tract. Data were analyzed by 2-way analysis of covariance. There was a significant interaction between dietary Ca:AvP ratio and phytase supplementation for weight gain (WG), feed intake (FI), and feed conversion ratio (FCR). In diets with no phytase, Ca:AvP ratio had a greater effect on WG, FI, and FCR compared with those fed diets without phytase. The orthogonal polynomial contrasts showed that the increase in dietary Ca:AvP ratio significantly decreased WG and FI in a quadratic manner, whereas FCR increased (P < 0.05) linearly with higher dietary Ca:AvP ratio. Increasing dietary Ca:AvP ratio led to a significant quadratic decrease in phytate degradation and significant linear decreases in P digestibility and bone ash. Phytase addition increased (P < 0.05) phytate degradation and improved (P < 0.05) energy, AA, and P digestibility at all levels of Ca:AvP with no interaction (P > 0.05) between the main factors. Digestibility of AA was positively correlated (P < 0.05) with the degree of phytate degradation. Increasing dietary Ca:AvP ratio significantly increased gizzard pH in a linear manner. In conclusion, phytase (1,000 phytase units/kg of feed) improved phytate, and P and AA digestibility at all Ca:AvP ratios evaluated in this study.