Description of 3 failed attempts to estimate the calcium equivalency of phytase for growth performance and tibia ash of broiler chickens when using graded dietary levels of limestone

Three broiler experiments were conducted to estimate the Ca equivalency of a novel phytase using direct and indirect methods. All 3 experiments employed 4 concentrations of limestone to create 4 reference diets, deficient in nonphytate P, with increasing dietary Ca. Phytase was supplemented to the lowest Ca reference diet at 350, 700, 1,400, or 2,800 FYT/kg in experiment (Exp.) 1 and Exp. 2 and at 500, 1,000, 2,000, or 4,000 FYT/kg in Exp. 3. Broilers were fed from d 8 to 10 and 20 to 24, 19 to 21, or 7 to 10 and 7 to 21 posthatching in Exp. 1, 2, or 3, respectively. Diet did not affect growth performance or tibia ash in Exp. 1. Reducing the dietary Ca linearly (P < 0.05) increased body weight gain (BWG) and feed intake (FI) in Exp. 2 or Exp. 3. Feed conversion ratio (FCR) was decreased (linear or quadratic, P < 0.05) as dietary Ca was reduced in Exp. 2 or Exp. 3 (d 7-21). Tibia ash percent linearly (P < 0.05) decreased as dietary Ca decreased in Exp. 3 but only from d 7 to 21 and phytase increased (linear or quadratic, P < 0.05) FI and BWG, and decreased FCR. In Exp. 1 (d 8-10) and Exp. 2, apparent ileal digestibility (AID), total tract retention, and apparent digested and retained Ca or P increased (linear or quadratic, P < 0.05) as dietary Ca decreased. Phytase increased (linear or quadratic, P < 0.05) AID and apparent digested and retained Ca or P in Exp. 1 or Exp. 2. Due to the nature of the effect of dietary Ca on performance or tibia ash, it was not possible to use the indirect method to estimate the Ca equivalence of phytase in the current experiments. The total and digestible Ca equivalence of phytase could be estimated using the direct method. These experiments highlight challenges to consider when designing experiments to estimate the Ca equivalency for phytase in the future.

Application of enzyme matrix values for energy and nutrients to a wheat-corn-soybean meal-based broiler diet supplemented with a novel phytase, with or without a xylanase-β-glucanase, achieved a production benefit over a nutritionally adequate unsupplemented diet

The effect of applying an energy and nutrient matrix to a wheat-corn-soybean meal-based diet supplemented with a novel consensus bacterial 6-phytase variant (PhyG) and xylanase-β-glucanase on growth performance, bone mineralization, carcass weights, feed costs, and carbon footprint was evaluated. A randomized complete block design (3,300 Ross 308 mixed-sex birds; 60 pens, 12 pens per treatment) tested 5 treatments: 1) a positive control diet (PC), containing 0.92, 0.84, 0.71% Ca and 0.43, 0.38, 0.30% digestible P during 1 to 10, 11 to 21, and 22 to 32 d of age, respectively; 2) a negative control reduced in Ca, digestible P, digestible AA, ME, and Na by phase based on the PhyG dosing regimen (NC1); 3) NC1 supplemented with PhyG at 2,000, 1,500, and 1,000 FTU/kg by phase (NC1+PhyG); 4) as NC1 but additionally reduced in ME (NC2); and 5) NC2 supplemented with PhyG as in 3) plus 1,220 U/kg of xylanase and 152 U/kg of β-glucanase (NC2+PhyG+XB). Final (d 32) BW, overall (0-32 d of age) ADFI, FCR, d 10 and 32 tibia ash and carcass part weights were reduced or impaired (P < 0.05) in NC1 and NC2 vs. PC (d 32 BW -477 g/bird (23.4%) and -422 g/bird (20.7%), respectively). Growth performance (all measures, all phases) was improved and tibia ash (at 10 and 32 d of age), total carcass thigh, breast and leg weights were increased (P < 0.05) in NC1+PhyG vs. NC1, and NC2+PhyG+XB vs. NC2. Overall growth performance outcomes in NC1+PhyG and NC2+PhyG+XB were not different (P > 0.05) from the PC. Total feed cost and carbon footprint per kilogram BW gain (BWG) were reduced (P < 0.05) vs. PC in NC2+PhyG+XB [-0.052 € and -376 g CO2 eq./kg BWG, respectively] and NC1+PhyG [-0.038 € and -260 g CO2 eq./kg BWG, respectively]. The results validated the nutrient matrices in the test diets and highlighted a potential feed cost and environmental sustainability benefit which was greatest when the enzymes were applied in combination.

Research Note: Comparison of two methods to measure broiler tibia morphology

The skeletal integrity of chickens is an important area of research and detailed measures are needed to better understand the influence of experimental manipulation on bone health. The objective of this experiment was to compare 2 methods to measure the superficial tibiotarsus (tibia) morphology of broiler chickens collected in the wet laboratory (WL) or from digital images (DIG). The length, width at 90%, 75%, 50%, 25%, and 10% of the length, proximal and distal head width, medial, lateral, and distal intercondylar groove depth (ID), and proximal head angle were measured on the right and left tibias collected from broilers in 2 experiments (E1, E2). In both experiments, tibias had a greater width at 90% of the length when measured with the WL method compared with the DIG method (P ≤ 0.04), while tibias measured with the DIG method had a greater length, distal ID, and widths at 10%, 25%, 50%, and 75%, of the length compared with the WL method (P < 0.0001). In E1, tibias measured with the DIG method had a greater medial, lateral, and distal ID compared with the WL method (P ≤ 0.04). In E2, compared with the DIG method, tibias measured with the WL method had a greater distal head width and lateral ID, yet a shallower distal ID (P ≤ 0.03). The use of the DIG method provided more precise measures but, due to the limitations of measures from digital images and the opportunity for more accurate measures to be collected with the WL method, the WL method is recommended to measure the superficial morphology of broiler chickens because it was more accessible and practical.

Effects of phytase and coccidial vaccine on growth performance, nutrient digestibility, bone mineralization, and intestinal gene expression of broilers

A study was conducted to evaluate effects of phytase and coccidial vaccine on growth performance, bone mineralization, nutrient digestibility, and intestinal gene expression of broiler chickens. The experiment was conducted in a 2 × 4 completely randomized factorial arrangement with 6 replicates per treatment and 10 birds each. Applications of coccidiosis vaccine and different dietary treatments were the 2 main factors in the current study. The dietary treatments included 1) a positive control (PC; 0.90% Ca and 0.45% available P: avP); 2) a negative control (NC; 0.75% Ca and 0.30% AvP); 3) NC + 500 FTU/kg of phytase (NC + 500PHY); and 4) NC + 1500 FTU/kg of phytase (NC + 1500PHY). Data were analyzed using SAS by 2-way ANOVA via GLM procedure. The statistical significance was set at P ≤ 0.05, and means were further separated using Tukey's Test. The results indicated that vaccination had no effect on growth performance except for feed intake from 0 to 14 d but negatively (P < 0.05) regulated bone ash and Ca digestibility. Birds fed with the Ca and P-reduced diet (NC) showed a lower BWG and bone ash compared to birds fed with the normal diet (PC), but supplementing phytase mitigated the negative effects on those birds. Broilers fed the NC diet had higher (P < 0.05) total Ca and P digestibility, and phytate degradation; supplementing phytase further increased P digestibility and phytate degradation of the broilers. A significant interaction (P < 0.05) between phytase and vaccination was observed, suggesting the vaccinated birds fed the PC diet and the unvaccinated birds fed the NC + 1500PHY increased calcium-sensing receptor gene expression compared with the unvaccinated birds fed the PC diet. In conclusion, in spite of coccidiosis vaccine, supplementing phytase at 1,500 FTU/kg alleviated the negative effects on growth performance, bone mineralization, and apparent ileal digestibility of P and phytate.

A simple daily dynamic feeding regimen for reducing phosphorus consumption and excretion in laying hens

Phosphorus metabolism in laying hens is a highly dynamic process over the course of the 24 h egg-laying cycle. Adjusting the phosphorus feeding regimen according to the daily egg-laying cycle may help to improve phosphorus utilization efficiency. Hy-Line Brown layers (n = 120; 70 wk old) were offered 4 different phosphorus daily regimens: (1) RR, fed regular phosphorus at both 09:00 and 17:00; (2) RL, fed regular phosphorus at 09:00 and low phosphorus at 17:00; (3) LR, fed low phosphorus at 09:00 and regular phosphorus at 17:00; (4) LL, fed low phosphorus at both 09:00 and 17:00. The regular and low phosphorus diets contained 0.32% and 0.14% non-phytate phosphorus, respectively. The feeding trial lasted for 12 wk. As a result, layers on the RL regimen had decreased laying rate (P < 0.05; 5 to 8, 9 to 12, and 1 to 12 wk) when compared to all other regimens. Layers on the LL regimen had decreased eggshell thickness and specific gravity (P < 0.05; wk 8) when compared to all other regimens, and had decreased egg shell strength (P < 0.05; wk 8) when compared to RL and LR regimens. When compared to the RR regimen (a common practice in the industry), layers on the LR regimen had: (1) identical laying performance and egg quality (P > 0.05); (2) decreased phosphorus excretion (P < 0.05) during the period of 09:00 to 17:00; (3) increased jejunal calbindin D28k protein expression (P < 0.05) 2 h after feeding in the morning; (4) decreased serum fibroblast growth factor 23 and calcitriol levels (P < 0.05), decreased jejunal type III sodium-phosphate cotransporter 2 gene and protein expression (P < 0.05), and decreased renal type III sodium-phosphate cotransporter 1 protein expression (P < 0.05), 2 h after feeding in the afternoon. In summary, when dietary phosphorus was supplemented in accordance with daily serum phosphorus rhythms (i.e., the LR regimen), laying performance and egg quality were well supported whilst significantly decreasing phosphorus consumption and excretion. Thus, serum phosphorus rhythms will need to be carefully maintained when developing dietary phosphorus-reduction strategies in laying hens.

Evaluation of the efficacy of a novel phytase in short-term digestibility and long-term egg production studies with laying hens

Three independent trials were conducted to evaluate the efficacy of a novel phytase in laying hens. Trial 1 used a total of 90 laying hens (Lohmann Brown, 33-wk-old) fed either a negative control (NC) diet with 0.09% non-phytate P (NPP) or NC supplemented with 187.5 or 375 FYT phytase/kg feed for 4 d before collection of excreta and ileal digesta to measure ileal digestibility and retention of Ca and P. In trial 2 and 3, a total of 108 laying hens (Hy Line Brown, 25-wk-old) and 360 hens (Lohman Brown, 25-wk-old) were used, respectively. In both trials, the hens were randomly assigned to 3 dietary treatments: NC with 0.1% NPP, positive control (PC) and NC plus 187.5 FYT phytase/kg feed, the experimental diets were fed for 12 wk, and egg production and bone mineralization were measured. The results showed that the ileal digestibility of P increased both linearly (P = 0.012) and quadratically (P = 0.01) with increasing supplementation of phytase in trial 1. In trial 2, phytase supplementation significantly improved egg production, egg weight, and feed conversion ratio and reduced the percentage of broken eggs during the overall trial duration compared with NC. In trial 3, phytase significantly improved egg production, egg weight, and feed intake and reduced the percentage of broken eggs during the entire trial duration. In addition, percentage and weight of bone Ca and P increased significantly with added phytase. In trial 2 and 3, there was no significant difference between PC and the phytase treatment. In conclusion, the novel phytase significantly increased the ileal digestibility of P in a short-term digestibility study and improved egg production and bone mineralization in a 12-wk laying cycle. Ileal digestibility of P rather than P retention in short-term digestibility studies as well as egg production and whole tibia mineralization in long-term studies should be measured to demonstrate the efficacy of phytase in laying hens.

A novel consensus bacterial 6-phytase variant added to phytate-rich diets totally replaced inorganic phosphate in broilers

The capacity of a novel bacterial 6-phytase variant (PhyG) to totally replace dietary supplemental inorganic phosphate (Pi) in broilers aged one day old was evaluated using a phased dosing strategy and reduction in dietary phytate. A total of 1,248 one-day-old Ross 308 broilers were assigned to 24 pens (52 birds/pen, 12 pens/diet, six each males and females) in a complete randomised block design with a 2×2 factorial arrangement (two diets, two genders). Diets comprised: (1) a positive control (PC) based on maize, wheat and soybean meal, containing Pi from monocalcium phosphate and 2,000 XU/kg xylanase, and; (2) an inorganic phosphate-free (IPF) diet equivalent to PC but with reduced Ca (-2.0 g/kg) and supplemented with PhyG at 3,000, 2,000 and 1000 FTU/kg from d 0 to 11 (3.4 g/kg phytate-P (PP)), d 11 to 22 (3.3 g/kg PP) and d 22 to 42 (2.8 to 2.9 g/kg PP), respectively. A negative control was not included for animal welfare reasons. Tibias were collected on d 11, 22 and 42 from two birds/pen. Treatment IPF maintained or improved average daily gain (ADG), average daily feed intake and feed conversion ratio (FCR) vs PC during all phases; Body weight was higher in the IPF treatment than the PC at d 42 (+3.97%, P<0.01) and ADG during d 0 to 42 (+4.10%, P<0.01). Overall (d 0 to 42), treatment IPF improved FCR in males (-5 points vs PC, P<0.05) but not females. Tibia ash was equivalent in IPF and PC throughout, with no gender differences. In conclusion, when applied as a phased dosing strategy to diets with graded reduction in PP content, PhyG totally replaced supplemental Pi during all growth phases in males and females.

Body weight of young broilers fed with declining calcium and phosphorus contents during the starter period is irresponsive to changes in the skeleton

To evaluate the effect of reduced calcium (Ca) and available P (aP) levels in starter diets on growth performance and tibia, sternum and serum characteristics, and to assay the association between Ca and P (aP) intakes and these variables, 600 one-day-old broiler chicks (Ross 308) were used in a 21-days trial. Broilers were randomly allotted to five treatments with five replicate pens. Chicks were fed on one of the five starter diets that were formulated with a 10% reduction in the Ca and aP contents, starting from the control diet and hence, named as C (0.96% Ca, 0.45% aP), L1 (0.85% Ca and 0.42% aP), L2 (0.77% Ca and 0.38% aP), L3 (0.68% Ca and 0.34% aP) and L4 (0.61% Ca and 0.31% aP). Declining dietary Ca and aP levels did not affect body weight and levels of Ca, P and alkaline phosphatase in serum, but reduced linearly feed intake, the feed conversion ratio and the bone weight and ash content. The Ca and aP intakes and Ca:aP ratio displayed a positive correlation with both tibia and sternum weights, and the mass of the bones were equally sensitive to dietary Ca and aP levels. In conclusion, the body weight of young broilers was irresponsive to changes in the skeleton when exposed to early dietary Ca and aP restrictions (up to 0.61% Ca and 0.31% aP) and the mechanostat had limits due to the association between Ca and aP intakes, and bone properties.

The adaptability of Hy-Line Brown laying hens to low-phosphorus diets supplemented with phytase

Body phosphorus homeostasis network allows laying hens to adapt to wide range of changes in dietary phosphorus levels. Phytase hydrolyzes phytate rendering phosphorus and reduces the laying hens' requirements for inorganic phosphate rock. Here, we demonstrate that there is no need to keep large safety margins in dietary phosphorus when hens are fed with phytase. Hy-Line Brown laying hens (n = 504) were randomly assigned to 7 treatments (6 replicates of 12 birds). A corn-soybean meal–based diet, with no inorganic phosphate rock, was formulated to contain 0.12% nonphytate phosphorus (nPP), 3.8% calcium, and 2,000 FTU/kg phytase. Inorganic phosphate rock (di-calcium phosphate) was supplemented into the basal diet to create 6 other diets containing 0.17, 0.22, 0.27, 0.32, 0.37, and 0.42% nPP. Levels of calcium carbonate and zeolite powder were adjusted to make sure all the 7 experimental diets contained the same nutrition levels (including calcium and phytase) except nPP. The diets were subjected to laying hens from 29 to 40 wk of age. As a result, when supplemented with 2,000 FTU/kg phytase, extra supplementation of inorganic phosphate rock had no effects (P > 0.05) on serum phosphorus levels, serum calcium levels, laying performance (laying rate, egg weight, feed intake, feed-to-egg ratio, and unqualified egg rate), egg quality (shell thickness, shell strength, albumen height, yolk color, and Haugh unit), and tibia quality parameters (breaking strength and ash, calcium, and phosphorus contents). Extra supplementation of inorganic phosphate rock linearly increased (P < 0.01) fecal phosphorus excretion and linearly decreased (P = 0.032) the apparent metabolizability of dietary phosphorus. While serum hormones and intestine gene expressions were varied within treatments, no consistent changes were found. In conclusion, the supplementation of inorganic phosphate rock (provided 0.05–0.30% extra nPP) to phytase-containing basal diets (2,000 FTU/kg; nPP = 0.12%) provided limited benefits to egg production performance in laying hens from 29 to 40 wk of age. Further investigating the body phosphorus homeostasis would help to understand the nutritional and physiological reasonability of formulating low-phosphorus diets in the laying hen industry.

Effects of available phosphorus source and concentration on performance and expression of sodium phosphate type IIb cotransporter, vitamin D-1α-hydroxylase, and vitamin D-24-hydroxylase mRNA in broiler chicks

This experiment was conducted to examine the effect of 2 phosphorus (P) sources on broiler performance to day 14. The P bioavailability was estimated using bird performance and tibia ash measurements, whereas P digestibility, intestinal P transporter, kidney vitamin D-1α-hydroxylase, and vitamin D-24-hydroxylase mRNA abundances were also determined. Slope regression analysis was used to determine the bioavailability of dicalcium phosphate (Dical P) and nanocalcium phosphate (Nano P) with dietary available P (AvP) set to 0.20% P (control) using AvP from the major ingredients and Dical P. The experimental treatments were achieved by supplementation with either Dical P or Nano P to generate 0.24, 0.28, 0.32, and 0.36% AvP. A total of 648-day-old unsexed broiler chicks were divided into 72 birds per treatment (8 replicate cages of 9 birds). Slope regression analysis showed positive linear relationships between BW, feed intake (FI), tibia ash weight (TAW), and tibia ash percentage (TAP) with dietary Dical P and Nano P levels. Comparisons between regression slopes for Dical P and Nano P fed birds were not significantly different for BW, feed intake, tibia ash weight, and tibia ash percentage, indicating similar P bioavailability from Dical P and Nano P. There were interactions between P source and AvP for feed efficiency (FE) and apparent ileal P digestibility (AIPD). Dicalcium phosphate had greater FE than Nano P at 0.28% AvP and greater AIPD than Nano P at 0.24% AvP. The addition of AvP from Dical P and Nano P resulted in reduced sodium phosphate cotransporter mRNA abundance in the duodenum in a dose–dependent response. In the kidney, vitamin D-1α-hydroxylase mRNA abundance was greater at 0.36% Nano P compared with control, but there was no difference with Dical P. There was no difference in vitamin D-24-hydroxylase mRNA abundance between control and supplementation with Nano P or Dical P. In conclusion, Nano P and Dical P had the same bioavailability but had different effects on gene expression.

Limestone particle size, calcium and phosphorus levels, and phytase effects on live performance and nutrients digestibility of broilers

Limestone particle size (PS) affects its solubility and thus can influence broiler performance by altering the rate of calcium (Ca) release into the gastrointestinal tract. The objective of this research was to determine, using 2 × 2 × 2 factorial arrangement, the influence of PS (fine and coarse) and supplemented phytase (0 and 1,000 FYT/kg) in diets formulated with 2 Ca and P_i levels (positive control [PC]; negative control [NC]) on live performance, bone ash, and apparent ileal nutrients digestibility (AID). Starter PC: 0.9 Ca and 0.45 Pi; NC: 0.72 Ca and 0.03 Pi. Grower PC: 0.76 Ca and 0.38 Pi; NC: 0.58 Ca and 0.23 Pi. The 8 diets were assigned randomly to a total of 1,512 birds, with 21 birds per pen and 9 pens per treatment. The main effects of PS and Ca and P_i levels had no influence on feed intake (FI), body weight gain (BWG), or feed conversion ratio. Adding phytase improved BWG by 8 g and 50 g and FI by 25 g and 56 g at 0–14 D (P ≤ 0.05) and 0–35 D (P ≤ 0.05), respectively. Interaction between Ca and P_i levels and phytase improved BWG and FI for 0–14 D (P ≤ 0.05) and BWG during 15–28 D (P ≤ 0.05) for PC without phytase and for PC and NC with phytase when compared with NC without phytase. Birds fed PC without phytase, or either PC or NC with phytase were about 96 g heavier than NC without phytase. Birds fed either PC or NC diet with coarse limestone or PC with fine limestone gained approximately 14 g more (P ≤ 0.05) than birds fed NC with fine limestone for BWG at 0–14 D (P ≤ 0.05). Phytase increased tibia bone ash (14 D) by 1% (P ≤ 0.05). AID of Ca and P_i at 14 D was improved (P ≤ 0.05) by 66% when phytase was added to coarse limestone. Results indicate that phytase improved broiler performance without being affected by PS. Furthermore, phytase had greater influence on coarse limestone than on fine limestone for bone ash and AID. Ca and P_i levels were the most influential factors in determining bone ash although phytase inclusion could lead to an improvement during early days.

Genetic parameters for bone ash and phosphorus utilization in an F2 cross of Japanese quail

The main objective of this study was to perform quantitative genetic analyses of tibia and foot ash traits, which might serve as proxy traits to improve phosphorus utilization (PU) in a breeding program. Additionally, data for ash concentration in tibia and foot were compared with data for total amount of ash. Heritabilities for bone ash traits and genetic and phenotypic correlations between bone ash traits and PU were estimated. A total of 887 F₂ birds, established from 2 Japanese quail lines divergently selected on social reinstatement behavior, were provided a P deficient diet. In a metabolic study, feed consumption was measured and total excreta collected for each bird separately. Afterwards, birds were euthanized, the bones obtained and incinerated. Bone ash data showed a heritability of 0.230 (amount of tibia ash) to 0.342 (amount of foot ash), which was higher than estimated for PU, P retention, calcium utilization (0.120–0.174), and performance traits (0.088–0.114). The strongest genetic and phenotypic correlations between PU and bone ash traits were detected for the amount of foot ash with 0.549 and 0.527, respectively. Genetic and phenotypic correlations were stronger between PU and ash amount than between PU and ash percentage, irrespective of bone. Therefore, ash amount was considered a better trait than ash percentage to reflect PU. Strong genetic and phenotypic correlations were detected between the amount of foot and tibia ash (0.887 and 0.901, respectively). Phenotypic and genetic correlations between ash amount and PU or calcium utilization were almost identical, irrespective of bone. Foot ash is as suitable as tibia ash, but easier to determine. Bone ash data, especially the amount of foot ash, seem to be suitable indirect selection criteria for P efficiency breeding.

Lack of a relationship between plasma fibroblast growth factor-23 and phosphate utilization in young chicks

Fibroblast growth factor 23 (FGF-23) is proposed to be the hormone that controls phosphate (P) homeostasis in chickens. This study was initiated to investigate the effect of feeding young chicks diets that were either adequate (0.45%) or marginal (0.25%) in available P content on plasma FGF-23 levels. The dietary level of available P significantly (P ≤ 0.05) affected bone mineralization and bone length, but was without effect (P > 0.05) on growth rate and circulating FGF-23 concentrations. Substantial individual variation in bone mineralization and plasma FGF-23 levels was observed, and the correlation between these two variables was non-significant (P > 0.05). This suggested that there was no alteration in FGF-23 activity in response to suboptimal dietary P intake. The relationship of these observations to studies on the immunosuppression of FGF-23 activity is subsequentlydiscussed.

Minerais séricos, características morfométricas ósseas e deposição de minerais ósseos de frangos de corte alimentados com dieta com inclusão de bentonita

RESUMO O objetivo deste trabalho foi avaliar a concentração sérica de cálcio, cloretos, ferro, fósforo e magnésio, as características morfométricas ósseas e a deposição de cálcio e fósforo nas tíbias de frangos de corte recebendo dieta com zero, 0,25 ou 0,50% de bentonita. Um ensaio foi conduzido com 288 frangos de corte de 14 a 21 dias de idade, submetidos a três dietas experimentais: sem inclusão (0,0); com inclusão de 0,25 e com inclusão de 0,50% do adsorvente bentonita. Não foram observadas diferenças (P>0,05) no desempenho das aves, nos níveis séricos de cálcio, cloretos, ferro e magnésio, no entanto os níveis de fósforo foram reduzidos (P<0,05) nas aves que ingeriram dieta com 0,50% de bentonita. Em relação às tíbias, observou-se redução (P<0,05) na matéria mineral (g e %) e no teor de cálcio com a inclusão de 0,50% de bentonita. Houve redução (P<0,05) nos níveis de fósforo das tíbias com a inclusão de 0,25 e 0,50% de bentonita. Conclui-se que a inclusão de até 0,50% do adsorvente de micotoxinas bentonita na dieta de frangos de corte não altera o desempenho zootécnico das aves. A inclusão de 0,25% de bentonita, na dieta de frangos de corte, não altera a concentração dos minerais séricos e a deposição de minerais nas tíbias, entretanto a inclusão de 0,5% reduz os níveis séricos de fósforo, o teor de matéria mineral e a concentração de cálcio e fósforo ósseos, sem afetar as características morfométricas ósseas.

Effect of a microbial phytase on growth performance, plasma parameters and apparent ileal amino acid digestibility in Youxian Sheldrake fed a low-phosphorus corn-soybean diet

Objective

This study investigated the effect of microbial phytase supplementation on growth performance, tibia ash, plasma parameters, apparent ileal digestibility (AID) of amino acid (AA) and apparent digestibility of nutrients in Youxian Sheldrakes fed with low-phosphorus (P) corn-soybean diets.

Methods

A total of 350 Youxian Sheldrakes (7d old) were randomly divided into 5 treatment groups: positive control (PC) group has adequate available P diet (0.42% and 0.38%, starter and grower), negative control (NC) group were deficient in available P (0.32% and 0.28%, starter and grower) and NC diet was supplemented with 3 levels of microbial phytase (500, 750, and 1,000 U/kg).

Results

Dietary supplementation of phytase in NC diet improved the average daily gain, increased the levels of serum calcium (Ca), tibia Ca and P, AID of AA and apparent digestibility of energy and Ca in starter stage (p<0.05). There was an increased (p<0.001) in the utilization of P from 17.3% to 23.9%. Phytase supplementation (1,000 U/kg) has shown that the AID of His, Thr, Val, indispensable AA, Glu, Pro, and dispensable AA was higher (p<0.05) than that of NC. Moreover, phytase supplementation improved (p<0.05) serum and tibia Ca and P, AID of AA and apparent digestibility of dry matter, crude protein, energy, P and Ca, and reduced (p<0.05) feed to gain ratio (F/G) and the levels of serum alkaline phosphatase in grower stage. Likewise, an increase (p<0.001) in the utilization of P was noticed from 12.6% to 17.2%. Supplement phytase at 750 U/kg improved the AID of His, Thr, Asp, Cys, Pro, and Ser (p<0.05).

Conclusion

The microbial phytase supplement could improve growth performance, AID of some AA and apparent utilization of other nutrients in Youxian Sheldrakes, and reduce excreta P load to environment.