Towards a digestible calcium system for broiler chicken nutrition: A review and recommendations for the future

Determination of the standardized ileal digestible calcium requirement of Ross broilers from hatch to day 14 post-hatch

An experiment was conducted to determine the standardized ileal digestible (SID) calcium requirement of fast-growing broilers from hatch to d 14 post-hatch. Ross 308 (n = 360) male broilers were obtained on day of hatch and allocated to 1 of 5 treatments in battery cages. There were 6 birds per cage and 12 pens per treatment. Four treatments were formulated to contain 0.60%, 0.46%, 0.32% or 0.18% SID Ca. The final treatment was formulated using total Ca to meet or exceed all nutrient requirements, including 0.90% total Ca and 0.49% non-phytate P (nPP), using the same ingredients. This treatment was the reference diet for comparison and validation of the SID Ca diets. Birds and feed were weighed at placement and on d 14. Tibias and ileal contents were obtained on d 14 and excreta was collected per pen and pooled on d 14. Data were analyzed using JMP Pro and requirements were estimated using 3 different non-linear regression models. Increasing the SID Ca content in the diet from 0.18% to 0.60% improved (quadratic, P < 0.05) body weight gain and mortality corrected feed conversion ratio (mFCR). The estimated SID Ca requirement to optimize gain or mFCR was between 0.39% and 0.52%. Tibia ash percent and weight increased (quadratic, P < 0.05) as SID Ca content in the diet increased and the estimated SID Ca requirement was between 0.32% and 0.58%. Phosphorus utilization was improved in birds fed diets formulated using SID Ca compared with birds fed the reference diet. In conclusion, the SID Ca requirement of fast-growing broilers from hatch to d 14 was estimated between 0.534% and 0.398% when quadratic, straight-broken line, or quadratic-broken line regressions were used. These results agree with previously published data evaluating the SID Ca requirement of fast-growth broilers from hatch to d 10.

A comparative study on the effect of limestone particle size on performance, ileal digestibility of calcium and phosphorus, and bone characteristics in broilers and pullets

1. The effects of limestone particle size on growth performance, gastrointestinal tract (GIT) traits, ileal morphology, duodenal gene expression of calbindin, apparent ileal digestibility coefficients (AIDC) of calcium (Ca) and phosphorus (P) and tibia characteristics in broilers and pullets were assessed in broilers and pullets. These birds have different growth rates and likely different responses to parameters, such as particle size.2. A total of 240 chicks aged one day, 120 Ross 308 female broilers, and 120 Hy-Line pullets were allocated randomly into four treatments in a 2 × 2 factorial arrangement with two bird types (broilers vs. pullets) and two limestone particle sizes (<0.5 mm versus 1-2 mm) to give six replicates containing 10 chicks in each from 1 to 21 d of age.3. Feed intake and weight gain were greater (P < 0.001) and feed per gain (FCR) was better (P < 0.001) in broilers compared to pullets from 1 to 21 d of age. Greater villus width (P < 0.01), villus height (P < 0.001) and crypt depth (P < 0.01) were seen for broilers compared to pullets.4. Pullets fed coarse Ca particles had higher calbindin gene expression at 21 d of age (P = 0.05). Both AIDC of Ca and P were higher (P < 0.001) in broilers compared to pullets. The AIDC of Ca from 0.463 to 0.516 was increased (P < 0.05) by feeding coarse limestone particles. A significant interaction was found between bird type and limestone particle size (P < 0.01), where pullets fed coarse Ca particles had higher bone P concentration in tibia than broilers.5. Broilers had better ileum absorptive capacity and growth performance compared to pullets. The AIDC of Ca and P was higher in broilers than in pullets. Increased limestone particle size elevated villus height, AIDC of Ca and concentration of P in the tibia.

Digestible calcium equivalency of phytase and nutrient utilization of broiler chickens fed graded levels of limestone or phytase during the starter phase

The current study aimed to quantify the digestible calcium (Ca) equivalency of a new phytase (HiPhorius) in broiler chickens. A total of 1,152 male Cobb 500 broiler chickens were used in an experiment in which 8 diets consisting of graded levels of Ca supplied with limestone or graded levels of the phytase were fed. The 8 dietary treatments were based on a corn-soybean meal diet containing 5.1 g/kg of Ca and 5.1 g/kg of phosphorus (P) as negative control (NC); the NC + 1.3, 2.6, or 3.9 g/kg of Ca from limestone; and the NC + 500, 1,000, 2,000, or 4,000 FYT/kg of phytase. Birds were fed the experimental diets for 3 d (from d 7 to 10) or 14 d (from d 7 to 21) to determine apparent ileal digestibility (AID) and apparent total tract retention (ATTR) of dry matter (DM), CP, Ca, and P. In the 10-day-old birds, increasing the levels of Ca decreased the AID of P and Ca (linear, P < 0.05). Increasing the levels of phytase quadratically improved (P < 0.05) the AID of Ca and P. The AID of DM and CP in the younger birds quadratically increased (P < 0.05) as the levels of Ca increased. There were linear and quadratic effects (P < 0.05) of increasing phytase level for the AID of DM and a linear effect (P < 0.05) for the AID of CP. In the 21-day-old birds, increasing Ca levels resulted in a linear decrease (P < 0.05) in the AID of CP and P, and a quadratic decrease (P < 0.05) in the ATTR of CP. Increasing phytase levels linearly and quadratically (P < 0.05) improved the AID and ATTR of CP, P, and the ATTR of Ca. The analyzed phytase activity in the diets supplemented with phytase ranged from 1,520 to 7,661 FYT/kg. The digestible Ca equivalence for dietary phytase at 1,520 to 7,661 FYT/kg ranged from 1.55 to 2.02 g/kg in the 10-day-old birds fed for 3 d and from 0.52 to 0.64 g/kg in 21-day-old birds fed for 14 d. The results showed the reduction in Ca level that could be accommodated by phytase supplementation, which is markedly different between the younger and older birds. Feeding duration influenced the impact of phytase supplementation on Ca and P digestibility, with better efficacy of phytase observed in the 10-day-old birds fed for 3 d. Also, the results showed the extra-phosphoric effects of phytase on the utilization of other essential nutrients such as protein and Ca.

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.

- Invited Review - Mineral composition and phosphorus digestibility in feed phosphates fed to pigs and poultry

Phosphorus (P) is a macro mineral needed for bone mineralization and cell membrane structure and P is also involved in several fundamental pathways of metabolism in the body. Because of the low concentration and digestibility of P in plant ingredients that are the main components of diets for poultry and pigs, feed phosphates are usually included in diets in addition to the P contributed by plant ingredients. The most widely used feed phosphates in poultry and swine diets are dicalcium phosphate (DCP) and monocalcium phosphate (MCP), but tricalcium phosphate (TCP), monosodium phosphate (MSP), and magnesium phosphate (MgP) may be used as well. Because feed phosphates are mostly produced from rock phosphate, feed phosphates have impurities that contain minerals other than P. Concentrations of P in feed phosphates range from 14.8% (MgP) to 25.7% (MSP). The standardized total tract digestibility (STTD) of P in pigs ranges from 71% (TCP) to 95% (MSP). The STTD of Ca and the standardized ileal digestibility (SID) of P and Ca in feed phosphates fed to pigs and poultry have been determined only in a few experiments. Available data indicate that the STTD of Ca and SID of P in MCP are greater than in DCP in both poultry and pigs, but the SID of Ca is similar between DCP and MCP fed to broilers. Information on mineral concentrations and digestibility values in feed phosphates is needed in diet formulation for pigs and poultry, but if diets are formulated to contain equal concentrations of digestible P and Ca, it is unlikely that animal performance will be impacted by the source of feed phosphates used in the diet.

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.

Research Note: Formulating broiler diets using digestible calcium significantly improved growth performance but reduced apparent ileal digestibility of calcium and phosphorus

An experiment was conducted to compare the use of a total and digestible Ca formulation system in broilers from hatch to d 37 post-hatch. Ross 308 (n = 288) male broilers were obtained and allocated to one of 2 dietary treatments in floor pens. There were 18 birds per pen and 8 replicate pens per diet. One diet was formulated using ingredient and nutrient recommendations for total Ca and the second diet was formulated using ingredient and nutrient recommendations for standardized ileal digestible (SID) Ca. All diets were formulated to be nutrient adequate using a 2-phase feeding program and including 0.19% available P (avP) and 0.209% total Ca or 0.073% digestible Ca from 1,000 FYT/kg of phytase. On d 17 and 37, tibias and ileal contents were obtained. From hatch to d 37, birds fed diets formulated using digestible Ca gained (P < 0.05) more and were more efficient (P < 0.05) compared with birds fed diets formulated using total Ca. There was no impact of formulation system on tibia ash or minerals. Litter pH (P < 0.05) was greater and litter dry matter (P < 0.05) was lower in birds fed the diets formulated using digestible Ca compared with those fed diets formulated using total Ca. Apparent ileal digestibility (AID) of Ca (P < 0.05), AID of P (P < 0.05) and digestible P intake (P < 0.05) were lower in birds fed diets formulated using digestible Ca compared with those formulated using total Ca at d 17 or 37. However, apparent ileal digested Ca and digestible Ca intake were not different between the experimental diets on d 17 or 37. In conclusion, formulating diets using digestible Ca improved weight gain and feed conversion ratio, but reduced the AID of Ca and P compared with birds fed diets formulated using total Ca. These findings might be reflective of the higher total Ca concentration in the diets formulated using digestible Ca compared with those formulated using total Ca.

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.

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.