Studies on the measurement of ileal calcium digestibility of calcium sources in broiler chickens

Ileal mineral digestibility and expression of nutrient transporter genes of broiler chickens in response to variable dietary total Ca and phytase supplementation are influenced by time on experimental diet and age of the birds

Two experiments were conducted to determine the impact of Ca, phytase, sampling time, and age on the digestibility (AID) of Ca and P and the expression of their transporters. Cobb 500 male chicks (N = 600) were used in each experiment and allocated to cages with 10 (Exp 1, 8-11 d) or 5 (Exp 2, 21-24 d) birds/cage and 10 (Exp 1) or 20 (Exp 2) reps/treatment. Treatments were a 2 × 3 factorial arrangement, with low (LOW) or standard (STD) Ca level and 3 phytase (PHY) levels (0, 300, or 3,000 FYT/kg). Ileal digesta were collected at 8, 12, 24, 48, and 72 h, and jejunum tissues at 12, 48, and 72 h after the start of feeding experimental diets. In Exp 1, there was no effect of Ca or phytase on the AID of Ca at 8, 12, or 24 h. Phytase increased the AID of P (P < 0.05) at all time points, and the magnitude was influenced by Ca. At 12 h, the mRNA level of P (NaPi-IIb) and Ca (CaSR) transporters was greatest in the LOW diets without phytase (Ca × PHY, P ≤ 0.06). In Exp 2, the STD diet decreased the AID of Ca and P (P < 0.05) at 8, 24, 48, or 72 h. Phytase increased the AID of Ca (P < 0.05) at 8, 12, and 24 h, and decreased the AID of Ca (quadratic, P < 0.05) in the STD diet (48 h). The AID of P (P < 0.05) increased with phytase at all sampling times. At 48 h, 3,000 FYT/kg decreased (P < 0.05) mRNA expression of NaPi-IIb and Ca transporter ATP2B1 in the STD diet (Ca × PHY, P < 0.05). In conclusion, to avoid adaptation of broilers to Ca and P deficiencies, the optimal time on experimental diets is ≤ 48 h for young broilers and ≤ 24 h in older birds due to up- or down-regulation of Ca and P transporters in response to dietary Ca, P, and phytase.

Calcium Nutrition of Broilers: Current Perspectives and Challenges

Calcium (Ca) plays an essential role in poultry nutrition as 99% of Ca is located in birds' skeletal system. However, oversupply of Ca rather than deficiency of Ca is the current concern in commercial broiler diets. Calcium is an inexpensive dietary nutrient due to the cheap and abundant availability of limestone, the major Ca source; therefore, little attention was given to the oversupply of Ca in the past. The recent shift in the use of digestible P in broiler feed formulations has necessitated a closer look at digestible Ca, as Ca and P are interrelated in their absorption and postabsorptive utilisation. In this context, data on ileal digestibility of Ca and P in ingredients has been determined. Preliminary data on the digestible Ca and digestible P requirements for the different growth stages of broilers have also recently become available. The present review focusses on these recent advances in Ca nutrition. In addition, aspects of homeostatic control mechanisms, different Ca sources and factors influencing Ca digestibility in poultry are covered.

Requirement of digestible calcium at different dietary concentrations of digestible phosphorus for broiler chickens 3. Broiler finishers (d 25 to 35 post-hatch)

An experiment was conducted to determine the digestible calcium (Ca) and digestible phosphorous (P) requirements of 25 to 35-day-old broiler chickens. Fifteen corn-soybean meal-based diets containing 2.0, 2.5, 3.0, 3.5, and 4.0 g/kg standardized ileal digestible (SID) Ca and 2.5, 3.5, and 4.5 g/kg SID P were fed to broilers from d 25 to 35 post-hatch. Each experimental diet was randomly allocated to 6 replicate cages (8 birds per cage). Body weight and feed intake were recorded, and the feed conversion ratio was calculated. On d 35, birds were euthanized to collect the ileal digesta, tibia, and carcass for the determination of ileal Ca, and P digestibility, concentrations of ash, Ca, and P in tibia and the retention of Ca and P in the carcass. Titanium dioxide (5.0 g/kg) was included in all diets as an indigestible indicator for the ileal digestibility measurement. Feed intake and total excreta output were measured during the last 4 d of the experimental period for the measurement of apparent total tract retention of Ca and P. Fixed effects of the experiment were dietary concentrations of SID Ca and SID P and their interaction. If the interaction or main effects were significant (P < 0.05), the parameter estimates for second-order response surface model (RSM) were determined using General Linear Model procedure of SAS. The maximum response was not predicted for most of the parameters (including growth performance and tibia) as the Ca effect was linear which indicated that the highest level of Ca employed in the study may have not been high enough. The requirement of dietary SID Ca for maximization of these parameters, therefore, depends on the dietary SID P concentration when the dietary SID Ca is within 2.0 to 4.0 g/kg. However, based on the factorial analysis, the highest weight gain was observed at 3.5 g/kg SID P and 3.5 g/kg SID Ca concentrations. Tibia ash was higher in birds fed 4.5 g/kg SID P and was unaffected by dietary SID Ca concentrations. However, based on overall findings, a combination of 3.5 g/kg SID P and 3.0-3.5 g/kg SID Ca may be recommended for the optimum tibia ash. The recommended SID Ca requirements (at 3.5 g/kg SID P) for weight gain (3.5 g/kg or 6.4 g/kg total Ca) and tibia ash (3.0-3.5 g/kg or 5.5-6.4 g/kg total Ca) are lower than the current Ca recommendations (7.8 g/kg total Ca equivalent to 4.25 g/kg SID Ca; Ross, 2019) for broiler finishers, suggesting possible excess of Ca in diets formulated based on the current recommendation.

Effects of limestone solubility on the efficacy of a novel consensus bacterial 6-phytase variant to improve mineral digestibility, retention, and bone ash in young broilers fed low-calcium diets containing no added inorganic phosphate

This study evaluated the effect of limestone solubility on the capacity of a novel consensus bacterial 6-phytase variant (PhyG) to improve phosphorus (P) and calcium (Ca) digestibility, retention, and utilization in low-Ca broiler diets containing no added inorganic phosphate (Pi). Male Ross 308 broilers (n = 1,152) were fed one of 16 experimental diets from 11 to 21 d of age in a randomized complete design (12 birds/cage, 6 cages/treatment). Diets comprised three positive controls (PC3, PC2, and PC1) containing 1.8, 1.2, or 0.6 g/kg MCP-P and 7.7, 7.0, or 6.2 g/kg Ca, respectively, and a negative control (NC) containing no added Pi (4.4 g/kg P; 2.8 g/kg phytate-P) and 5.5 g/kg Ca from either low or high solubility limestone (LSL or HSL, respectively, [with 42% and 97% solubility after 5 min at pH 3.0]), supplemented with 0, 250, 500, 1,000, or 2,000 FTU/kg of PhyG. Fecal samples collected on days 18 to 20 and ileal digesta collected on day 21 were analyzed for titanium dioxide, Ca, P, and phytate (IP6, inositol hexakisphosphate). Tibias (day 21) were analyzed for ash content. Data were analyzed by factorial analysis (2 limestone solubilities × 4 MCP-P levels and 2 limestone solubilities × 5 phytase dose levels) and exponential regression. Increasing dose levels of PhyG resulted in an exponential increase (P < 0.01) in the apparent ileal digestibility (AID) of P, ileal digestible P content of the diet, ileal IP6 content, and IP6 disappearance in birds fed either HSL or LSL diets, but AID Ca and ileal digestible Ca were exponentially increased by the phytase only in HSL diets (P < 0.01). Relative to HSL, the LSL increased AID P, ileal digestible P, and IP6 disappearance (P < 0.05) but reduced AID Ca, ileal digestible Ca, and retainable Ca (P < 0.05), resulting in reduced retainable P and tibia ash. Phytase exponentially increased the apparent total tract digestibility of P, retainable P, and tibia ash in HSL and LSL diets, but at or above 500 FTU/kg values were higher in HSL than LSL (interaction P < 0.05). The findings highlight that phytase dose-response effects on mineral digestibility and utilization are different for high- and low-solubility limestones, and it is therefore recommended to use digestible rather than total Ca content during diet formulation to ensure an optimal balance of Ca and P, especially in low-Ca diets. In diets containing HSL, higher phytase dose levels may be needed to compensate for the low digestible P content of the basal diet.

Gastrointestinal digestibility insights of different levels of coated complex trace minerals supplementation on growth performance of yellow-feathered broilers

This study was designed to evaluate the optimum additional level of coated complex trace minerals (TMs) and its impacts on the growth performance of broilers through measurement of digestibility of nutrients and intestinal development. In a 56-day trial, a total of 360 one-day-old male yellow-feathered broilers were randomly divided into six dietary treatment groups. Each treatment contained six replicates, with 10 birds. The control group was supplemented with 1,000 mg/kg of uncoated complex TMs in the basal diet (UCCTM1000). The remaining 5 treatments were degressively supplemented with coated complex TMs from 1,000 to 200 mg/kg in the basal diet, which were considered as (CCTM1000), (CCTM800), (CCTM600), (CCTM400), (CCTM200), respectively. Results: On comparing the UCCTM1000 supplementation, the CCTM1000 supplementation decreased the feed to gain ratio (F/G) (P < 0.05), increased digestibility of crude protein (CP) (P < 0.05), crude fat (CF) (P < 0.05), villus height (VH) of duodenum (P < 0.05), and the mRNA expression level of occludin in jejunal mucosa (P < 0.05). In addition, the F/G was lower in the CCTE600 group than that in the CCTE200 group (P < 0.05). The VH to crypt depth (CD) ratio (V/C) of jejunum and ileum in the CCTM400 and CCTM600 groups was higher (P < 0.05) than that in the CCTM1000 group. The serum endotoxin and D-lactate level and CP digestibility were increased by dietary coated complex TMs addition level. The mRNA expression levels of claudin-1 and ZO-1 in the CCTM600 group were higher (P < 0.05) than that in the CCTM1000 group. In conclusion, adding 600 mg/kg of coated complex TMs showed the minimum F/G and the maximum crude protein digestibility and intestine development of yellow-feathered broilers compared with other treatments. This supplementation level of coated complex TMs could totally replace 1,000 mg/kg of uncoated complex TMs to further decrease the dose of TMs and raise economic benefit.

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.

Requirement of digestible calcium at different dietary concentrations of digestible phosphorus for broiler chickens. 2. Broiler growers (d 11 to 24 post-hatch)

An experiment was conducted to determine the digestible calcium (Ca) and digestible phosphorous (P) requirements of 11 to 24 d old broiler chickens. Eighteen corn-soybean meal-based diets containing 1.80, 2.35, 2.90, 3.45, 4.00, and 4.55 g/kg standardized ileal digestible (SID) Ca and 3.5, 4.5, and 5.5 g/kg SID P were fed to broilers from d 11 to 24. Each experimental diet was randomly allocated to six replicate cages (8 birds per cage). Body weight and feed amount were recorded at the start and end of the experiment and the feed conversion ratio was calculated. On d 24, birds were euthanized to collect ileal digesta, tibia, and carcass for the determination of digestible Ca and P, the concentration of ash, Ca and P in tibia and the retention of Ca and P in the carcass, respectively. Titanium dioxide (5 g/kg) was included in all diets as an indigestible indicator for apparent ileal digestibility measurement. Total excreta output was measured during the last 4 d of the experimental period for the measurement of apparent total tract retention of Ca and P. Fixed effects of the experiment were dietary concentrations of SID Ca and SID P and their interaction. If the interaction or main effect was significant (P < 0.05), the parameter estimate for second-order response surface model was determined using General Linear Model procedure of SAS. The weight gain of broiler growers was optimized at the SID P concentration of 3.5 g/kg and SID Ca concentrations between 2.35 and 4.00 g/kg. At 3.5 g/kg SID P concentration, the required SID Ca for maximum weight gain was determined to be 3.05 g/kg, which corresponded to SID Ca to SID P ratios of 0.87. The concentration of SID Ca that maximized tibia ash at 3.5 g/kg SID P was 3.69 g/kg, which corresponded to SID Ca to SID P ratio of 1.05. Maximizing bone ash requires more Ca than maximizing weight gain. Carcass Ca and P retention were reflective of total tract Ca and P retention values. The estimated SID Ca requirements (at 3.5 g/kg SID P) for both maximized weight gain (3.05 g/kg or 6.11 g/kg total Ca) and bone ash (3.69 g/kg or 7.28 g/kg total Ca) are lower than the current Ca recommendation (8.70 g/kg total Ca equivalent to 4.03 g/kg SID Ca; Ross, 2019) for broiler growers, indicating possible oversupply of Ca in diets formulated based on the current recommendation.

Comparison of Coated and Uncoated Trace Minerals on Growth Performance, Tissue Mineral Deposition, and Intestinal Microbiota in Ducks

Abnormally low or high levels of trace elements in poultry diets may elicit health problems associated with deficiency and toxicity, and impact poultry growth. The optimal supplement pattern of trace mineral also impacts the digestion and absorption in the body. For ducks, the limited knowledge of trace element requirements puzzled duck production. Thus, the objective of this study was to investigate the influence of dietary inclusions of coated and uncoated trace minerals on duck growth performance, tissue mineral deposition, serum antioxidant status, and intestinal microbiota profile. A total of 1,080 14-day-old Cherry Valley male ducks were randomly divided into six dietary treatment groups in a 2 (uncoated or coated trace minerals) × 3 (300, 500, or 1,000 mg/kg supplementation levels) factorial design. Each treatment was replicated 12 times (15 birds per replicate). Coated trace minerals significantly improved average daily gain (p < 0.05), increased Zn, Se, and Fe content of serum, liver, and muscle, increased serum antioxidant enzyme (p < 0.05) and decreased the excreta Fe, Zn, and Cu concentrations. Inclusions of 500 mg/kg of coated trace minerals had a similar effect on serum trace minerals and tissue metal ion deposition as the 1,000 mg/kg inorganic trace minerals. Higher concentrations of Lactobacillus, Sphaerochatea, Butyricimonas, and Enterococcus were found in birds fed with coated trace minerals. In conclusion, diets supplemented with coated trace minerals could reduce the risk of environmental contamination from excreted minerals without affecting performance. Furthermore, coated trace minerals may improve the bioavailability of metal ions and the colonization of probiotic microbiota to protect microbial barriers and maintain gut health.

Determination of the standardized ileal digestible calcium requirement of male Arbor Acres Plus broilers from day 11 to 24 post-hatch

Male broilers (n = 576) were obtained and allocated to 96 cages with 6 birds per cage. From hatch to d 24, 16 randomly allocated cages were fed a nutrient adequate reference diet. The reference diet was formulated to contain 0.96 and 0.87% total Ca from hatch to d 10 and d 11 to 24, respectively. The remaining 80 cages were fed a nutrient adequate diet, formulated to contain 0.50% standardized ileal digestible (SID) Ca from hatch to d 10. On d 11, five diets containing 0.56, 0.46, 0.36, 0.26, or 0.16% SID Ca were randomly assigned to 16 cages per diet. Means were separated using polynomial contrasts and Dunnett's Multiple Comparison tests. From hatch to d 10, birds fed diets formulated to contain 0.50% SID Ca gained more (P < 0.05) compared with birds fed the reference diet. From d 11 to 24, there was no effect of diet on feed intake or BW gain. Birds fed 0.46 or 0.16% SID Ca were less (P < 0.05) efficient compared with birds fed the reference diet. Birds fed 0.26 or 0.36% SID Ca were more efficient compared with birds fed all other levels of SID Ca (quadratic, P < 0.05). Tibia ash percent was greatest in birds fed 0.56 or 0.46% SID Ca, decreased (quadratic, P < 0.05) as dietary SID Ca decreased and was lower (P < 0.001) in birds fed the 0.26 or 0.16% SID Ca diets compared with birds fed the reference diet. Apparent ileal digestibility (AID) of Ca or retention of P was greater (P < 0.05) in birds fed the diets formulated using SID Ca compared with birds fed the reference diet. Apparent P retention was greatest in birds fed 0.36% SID Ca (quadratic, P < 0.05). Regression equations developed using P retention, AID of Ca, and percent tibia ash estimated the SID Ca requirement of 11 to 24-d-old broilers was 0.380, 0.488, and 0.515%, respectively. This corresponds to a SID Ca to available P ratio of 0.86 to 1.17.

Global survey of limestone used in poultry diets: calcium content, particle size and solubility

Limestone is used in poultry diets as a calcium (Ca) source. Feed formulation is often based on an estimate of limestone Ca content or, less frequently, wet chemistry analysis. However, limestone composition may vary, which has not previously been studied on a large scale. In this study, 641 limestone samples supplied to poultry feed mills in 40 countries across eight global regions were collected and analysed for macro- and micromineral content, particle size (geometric mean diameter, GMD), and in vitro solubility. Mean Ca content of fine limestone (GMD<1000 μm, n=566) was 37.8% (range 33.3-39.7%) and for coarse limestone (GMD>1000 μm, n=75) was 38.0% (range 34.7-40.0%). There was marked variation among and within regions in the concentration of other macro minerals and microminerals. Particle size (GMD) of fine limestone was 288 μm (range 37.7-991.9 μm) and 1,689 mm for coarse limestone (range 301.6-3,067.9 μm). In vitro solubility of fine limestone (5 min incubation, pH=3.0) was 68.4% (range 18.8 to 99.4%). Particle size only explained 52% of the variation in 5 min incubation solubility (R2=0.52). For coarse limestone, mean solubility (30 min incubation) was 65.5% (range 23.2-96%) which was not correlated (R2=0.09) with particle size. Particle size and solubility rate of limestone have been shown to alter Ca and phosphorus utilisation in broilers and laying hens. Hence, better understanding of variation in mineral analysis, particle size and solubility rate would enable more accurate feed inclusion and subsequently digestibility to support health and performance.

Requirement of digestible calcium at different dietary concentrations of digestible phosphorus for broiler chickens. 1. Broiler starters (d 1 to 10 post-hatch)

An experiment was conducted to determine the digestible calcium (Ca) and digestible phosphorous (P) requirements of 10-day-old broiler chickens. Fifteen corn-soybean meal-based diets containing 3.3, 3.9, 4.4, 5.0, and 5.5 g/kg standardized ileal digestible (SID) Ca and 4.0, 5.0, and 6.0 g/kg SID P was fed to broilers from d 1 to 10. Each experimental diet was randomly allocated to 6 replicate cages (12 birds per cage). Body weight and feed intake were recorded at the start and end of the experiment and the feed conversion ratio was calculated. On d 10, birds were euthanized to collect ileal digesta, toes and tibia for the determination of digestible Ca and P, toe ash concentration and the concentrations of ash, Ca, and P in tibia. Titanium dioxide (5 g/kg) was included in all diets as an indigestible indicator for apparent ileal digestibility measurements. Total excreta were collected from d 1 to 10 for the measurement of total tract retention of Ca and P. Fixed effects of the experiment were dietary concentrations of SID Ca and SID P and their interaction. If the interaction or main effects were significant (P < 0.05), the parameter estimates for second-order response surface model were determined using General Linear Model procedure of SAS software. The growth performance, bone mineralization and mineral utilization of broiler starters were found to be optimized at 5 g/kg SID P concentration. Required SID Ca for maximum weight gain and bone mineralization was determined to be 3.32 and 4.36 to 4.78 g/kg, respectively, at 5 g/kg SID P concentration, which correspond to SID Ca to SID P ratios of 0.66 and 0.87 to 0.96, respectively. The estimated SID Ca requirement for weight gain is lower than the current Ca recommendation (9.6 g/kg total Ca or 4.4 g/kg SID Ca) for broiler starters. However, bone mineralization is maximized around the current total Ca recommendation at 8.9 to 9.8 g/kg (4.36-4.78 g/kg SID Ca) and indicates that bone mineralization requires more Ca than growth performance.

Determination of the standardized ileal digestible calcium requirement of male Arbor Acres Plus broilers from hatch to day 10 post-hatch

Arbor Acres Plus male broilers (n = 1,152) were obtained at hatch and allocated to 1 of 6 diets from hatch to d 10 post-hatch. There were 16 replicate cages per diet and 12 birds per cage. Five of the diets were formulated to contain graded concentrations of standardized ileal digestible (SID) Ca at 0.60, 0.50, 0.40, 0.30, or 0.20%. A sixth reference diet was formulated using total Ca coefficients for each ingredient and contained 0.96% total Ca. Available P (avP) was maintained at 0.48% in all 6 diets. Data were subjected to an analysis of variance and the model included diet and block. Means were separated using contrasts to determine linear or quadratic effects of SID Ca and using the Dunnett's test to compare the reference diet to all SID Ca diets. There was no effect of graded levels of SID Ca on intake or gain. Birds fed diets containing 0.60, 0.50, 0.30, or 0.20% SID Ca ate (P < 0.05) or gained (P < 0.05) more compared with birds fed the reference diet. Mortality corrected FCR improved (linear, P < 0.05) as the SID Ca concentration in the diet increased from 0.20 to 0.60%. Tibia ash percent was greatest in birds fed 0.50% SID Ca and lowest in birds fed 0.20% SID Ca (quadratic, P < 0.05). Tibia ash percent was lower (P < 0.05) in birds fed diets formulated to contain 0.20% SID Ca compared with birds fed the reference diet. No other differences in tibia ash were reported. Apparent ileal digestibility (AID) or retention of P was greater (P < 0.05) in birds fed diets formulated using SID Ca compared with birds fed the reference diet. The AID of P increased (linear, P < 0.05) as the SID Ca content in the diet decreased from 0.60 to 0.20%. The AID or retention of Ca was similar in birds fed 0.60 or 0.50% SID Ca and increased as SID Ca decreased to 0.20% (quadratic, P < 0.05). Regression equations developed using bone ash and apparent P retention estimate the SID Ca requirement of Arbor Acres Plus broilers from hatch to d 10 post-hatch was 0.53 and 0.49%, respectively. This corresponds to a SID Ca to available P ratio of 1.1 to 1.02.

Comparison of the apparent ileal calcium digestibility of limestone in broilers and layers

1. The apparent ileal calcium (Ca) digestibility coefficients of two limestone sources in growing broilers and layers were determined in two separate experiments.2. In each experiment, two maize-based diets were developed with two limestone sources (A, experiment 1 and B, experiment 2) to contain either 8.0 g/kg Ca for broilers or 40 g/kg Ca for layers. The two sources differed in particle size, with limestone A being finer and limestone B being coarser. Each experimental diet was randomly allotted to six replicate cages and offered for 3 days from 19 to 21-day post-hatch to broilers and during 40 weeks of age to layers. The total tract Ca retention was also measured using the indicator ratios in the diet and excreta.3. In both experiments, the apparent ileal Ca digestibility, gizzard pH and gizzard Ca concentration were higher (P < 0.05) in layers than in broilers. The apparent ileal digestibility coefficient of limestone A for broilers and layers was 0.50 and 0.62, respectively. The corresponding values for limestone B were 0.43 and 0.70, respectively. The apparent total tract retention of Ca was similar (P > 0.05) between broilers and layers in both experiments, and between the two sources.4. The data show that the layers are more efficient in absorbing Ca from limestone than broilers.

True ileal calcium digestibility in soybean meal and canola meal, and true ileal phosphorous digestibility in maize-soybean meal and maize-canola meal diets, without and with microbial phytase, for broiler growers and finishers

1. Published data on the ileal Ca digestibility in soybean meal (SBM) and canola meal (CM), and the effect of microbial phytase on the Ca digestibility of these ingredients are limited. Therefore, two experiments were conducted, with the primary objective of determining the true ileal digestibility of calcium (Ca) in SBM and CM, without and with microbial phytase, during broiler grower (Experiment 1) and finisher (Experiment 2) periods. A secondary objective was to investigate the influence of microbial phytase on the true ileal digestibility of phosphorus (P), apparent digestibility of nitrogen (N) and minerals, and phytate disappearance in maize-SBM and maize-CM diets. Six experimental diets based on SBM and CM, with three phytase doses (0, 500 and 2000 FTU/kg), were fed to broilers from day 18 to 21 (Experiment 1) or 39 to 42 (Experiment 2) post-hatch. A Ca- and P-free diet, with no added phytase, was also developed to determine the endogenous Ca and P losses. Titanium dioxide was incorporated in all diets as an indigestible indicator. Each experimental diet was randomly allocated to six replicate cages (eight birds per cage). Apparent ileal digestibility was calculated using the indicator method and the true ileal digestibility was calculated by correcting for endogenous losses. Apparent total tract retention (ATTR) of Ca and P was also measured.2. Ileal endogenous losses of Ca and P were determined to be 236 and 310 mg/kg of dry matter intake (DMI), respectively, in broiler growers and 29 and 130 mg/kg of DMI, respectively, in broiler finishers. True ileal Ca digestibility coefficients of SBM and CM, without added phytase, were determined to be 0.51 and 0.53, respectively, in broiler growers and 0.33 and 0.22, respectively, in broiler finishers. Increasing phytase doses increased (P < 0.05) the true ileal Ca digestibility of CM in both broiler growers and finishers, but Ca digestibility of SBM increased (P < 0.05) only at the superdose (2000 FTU/kg) in broiler finishers. The ATTR of Ca (P < 0.001) in growers was higher in CM than in SBM and was increased in both ingredients by increasing phytase doses. In finishers, the ATTR of Ca was increased (P < 0.001) by both phytase doses in CM, but only by the superdose in SBM, resulting in an ingredient × phytase interaction (P < 0.001).3. True ileal P digestibility coefficients of maize-SBM and maize-CM diets, without added phytase, were determined to be 0.89 and 0.66, respectively, in broiler growers and 0.82 and 0.57, respectively, in broiler finishers. Supplemental phytase increased (P < 0.05) the true ileal P digestibility of the maize-CM diet in both broiler growers and finishers. However, the P digestibility of the maize-SBM diet was increased (P < 0.05) in broiler finishers only at the superdose (2000 FTU/kg). The ATTR of P was higher (P < 0.001) in the maize-SBM diet during both periods.4. The apparent ileal digestibility of N, Mg, K and Mn was higher (P < 0.001) in the maize-SBM diet for broiler growers and finishers. Phytase addition had no effect (P > 0.05) on the apparent digestibility of N and minerals in growers and finishers.5. Increasing phytase doses increased IP6 disappearance in the maize-CM diet, but not in the maize-SBM diet, resulting in an ingredient × phytase interaction (P < 0.001) for growers and finishers.6. In conclusion, true ileal Ca digestibility coefficients of SBM and CM for broilers were determined in this study. The findings confirmed the influence of broiler age of Ca digestibility. Superdosing of phytase increased the digestibility and ATTR of Ca in CM and SBM by two-fold compared to the normal phytase dose.

Trends in feed evaluation for poultry with emphasis on in vitro techniques

Accurate knowledge of the actual nutritional value of individual feed ingredients and complete diets is critical for efficient and sustainable animal production. For this reason, feed evaluation has always been in the forefront of nutritional research. Feed evaluation for poultry involves several approaches that include chemical analysis, table values, prediction equations, near-infrared reflectance spectroscopy, in vivo data and in vitro digestion techniques. Among these, the use of animals (in vivo) is the most valuable to gain information on nutrient utilization and is more predictive of bird performance. However, in vivo methods are expensive, laborious and time-consuming. It is therefore important to establish in vitro methods that are reliable, rapid and practical to assess the nutritional quality of feed ingredients or complete diets. Accuracy of the technique is crucial, as poor prediction will have a negative impact on bird performance and, increase feed cost and environmental issues. In this review, the relevance and importance of feed evaluation in poultry nutrition will be highlighted and the various approaches to evaluate the feed value of feed ingredients or complete diets will be discussed. Trends in and practical limitations encountered in feed evaluation science, with emphasis on in vitro digestion techniques, will be discussed.

Coarse limestone does not alleviate the negative effect of a low Ca/P ratio diet on characteristics of tibia strength and growth performance in broilers

The hypothesis was tested that an increased digestion of coarse compared with fine limestone can alleviate the negative effects of a low dietary Ca/P ratio on the growth performance and characteristics of tibia strength (CTS) in broilers. A total of 1,152 Ross 308 broiler chickens received a standard commercial starter feed from day 0 to 13. From day 14 onward, birds received 1 of 12 diets containing 1 of 6 Ca/P ratios (0.50, 0.75, 1.00, 1.25, 1.50, and 1.75) and 1 of 2 limestone particle sizes (<500 [fine] and 500 to 2,000 [coarse] μm) in a study with a 6 × 2 factorial arrangement of treatments. Total P content was fixed at 5.5 g/kg for all treatment diets. Each treatment was replicated 6 times with 16 birds per replicate pen. On day 20 and 21, twelve birds per pen were randomly selected from 4 of the 6 replicate pens for tibia analysis and digesta collection from different gut segments. The apparent Ca digestibility was higher for fine than coarse limestone in the jejunum (P = 0.043). However, this difference in Ca digestibility disappeared for the low, whereas it remained for the high Ca/P ratios in the proximal (P_interaction = 0.067) and distal (P_interaction = 0.052) ileum. In addition, coarse limestone improved apparent P digestibility in the proximal and distal ileum (P < 0.001) but not in the jejunum (P = 0.305). Regardless of limestone particle size, reducing dietary Ca/P ratio linearly improved apparent Ca and P digestibility in the proximal and distal ileum (P < 0.001). Moreover, decreasing dietary Ca/P ratio linearly (P < 0.001) and quadratically (P < 0.046) reduced the CTS. Reducing dietary Ca/P ratio linearly (P < 0.003) and quadratically (P ≤ 0.006) decreased body weight gain and increased feed conversion ratio. For both fine and coarse limestone, the optimal Ca/P ratio was 1.00 to 1.25 to optimize apparent Ca and P digestibility while maintaining growth performance and CTS. Reducing Ca/P ratio from 1.75 to 1.00 improved distal ileal Ca and P apparent digestibility from 36.6 to 53.7% and 48.0 to 58.3%, respectively. In conclusion, coarse limestone is equally digestible with fine limestone at a low Ca/P ratio but is less digestible at a high Ca/P ratio, and the optimal Ca/P ratio in the diet is 1.00 to 1.25 for both fine and coarse limestone.