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
Article information
Abstract
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.
INTRODUCTION
Calcium (Ca) and phosphorus (P) are the most important minerals in poultry diets to obtain the optimal productivity. Currently, the National Research Council (NRC) has recommended 9.0 g/kg Ca and 3.5 g/kg non-phytate phosphorus (NPP) for growing broiler chickens [1]. However, the recommended dietary concentrations of Ca and P for broiler chickens are still debatable. In addition, there are increasing environmental and economic concerns regarding P utilization, and therefore, broiler nutritionists currently make a great effort to minimize P concentrations in diets to the levels that do not damage broiler productivity. Thus, the current broiler industry has developed and adopted low NPP diets. Moreover, phytase is also widely used to optimize P utilization in the low NPP diets to date [2].
Dietary Ca concentrations are suggested to be adjusted according to dietary NPP concentrations due to potential antagonising effects of Ca on P utilization in the gastrointestinal tract of poultry [3]. This adjustment is likely more important when low NPP diets are fed to broiler chickens [4,5]. Furthermore, previous experiments have reported that Ca utilization can be improved by supplemental phytase in addition to improved P utilization [2,6]. Therefore, a greater reduction in the concentrations of Ca in low NPP diets containing phytase than the current NRC recommendations [1] can be practiced for broiler diets. However, limited data regarding the relationship between Ca and NPP concentrations in diets containing phytase are available for broiler chickens. In addition, Collett [7] suggested that high concentrations of Ca in poultry diets may impair litter quality by increasing litter moisture content. In addition, poor litter quality is often associated with footpad dermatitis (FPD) incidence, which has gained increasing attention in broiler industry [8]. Thus, we hypothesised that the FPD incidence would be decreased when broiler chickens are fed diets containing low concentrations of Ca. However, no experiments using growing broiler chickens have been conducted, in which dietary Ca concentration and FPD incidence has been studied.
The objective of the present experiment, therefore, was to investigate the effect of dietary Ca concentrations in low NPP diets containing phytase on growth performance, bone mineralization, litter quality, and FPD incidence in growing broiler chickens.
MATERIALS AND METHODS
Birds, diets, and experimental design
The protocol for this experiment was reviewed and approved by the Institutional Animal Care and Use Committee at Chung-Ang University.
A total of 1,800 21-day-old Ross 308 growing broiler chickens (initial body weight [BW] = 962±57.0 g) were used and raised in conventional floor pens (200×230×100 cm, width×length×height) for 14 days of growing period. Before the start of the experiment, all chickens were fed a commercial starter diet. All chickens were allotted to 1 of 6 dietary treatments with 6 replicates in a completely randomized design. Each replicate had 50 birds per cage. Six commercial-type experimental diets were formulated to provide different Ca concentrations of 4.0, 5.0, 6.0, 7.0, 8.0, or 9.0 g/kg in diets (Table 1). The concentrations of NPP in all diets were maintained at 3.0 g/kg, which was less by 15% than the current recommendation of NPP concentrations (3.5 g/kg) in diets fed to growing broiler chickens [1]. Phytase (Phyzyme XP, Danisco Animal Nutrition, Marlborough, UK) was also supplemented to all diets at the level of 1,000 fytase units/kg as simulated to the commercial type phytase-containing diets. The experimental diets were mash form. All diets were formulated to meet or exceed the National Research Council requirements for growing broiler chickens [1], with the exception of Ca and NPP (Table 1). The diets and water were provided ad libitum throughout the experiment. Initial room temperature was set at 24°C, and was maintained from 23°C to 25°C during the experiment. Fresh rice hulls were used as bedding materials in the cages at the start of the experiment. Each cage had 2 separate feeders and 1 automatic water bowl. A 24-hour lighting schedule was used throughout the experiment. The body weight gain (BWG) and feed intake (FI) were recorded at the end of the experiment. Mortality was recorded daily. Feed efficiency (G:F) was calculated by dividing BWG with FI that were adjusted with mortality.
Sample collection and chemical analysis
At the conclusion of the experiment (35 days of age), 2 birds per replicate with a BW close to the replicate mean BW (i.e., 12 birds per treatment) were euthanized by CO2 asphyxiation, then immediately dissected. Both left and right tibias were collected from each replicate (i.e., 2 birds) before analysis. The right tibias were detached from adhering tissues, and then dried at 100°C for 24 hours in a drying oven. Fat in dried right tibias was extracted with ethyl ether in a Soxhlet apparatus for 48 hours. Afterwards, the samples were dried at 100°C for 24 hours in a drying oven, then dried right tibias were ground to pass through a 1.0-mm screen. Grounded samples were ashed for 24 hours at 600°C in a muffle furnace to measure tibia ash contents [9,10]. Tibia Ca and P concentrations were analyzed in the ash of right tibia by inductively coupled plasma spectrometer (Optima 5300 DV, Perkin Elmer Inc., Shelton, CT, USA) as proposed by Kurtoğulu et al [11] with minor modification. The left tibias were used for breaking strength analysis using a texture analyser TA-HDi (Stable Micro Systems Ltd, Surrey, UK) according to the method described by Shaw et al [12].
Litter samples were collected from 3 areas in the cage (i.e., near the waterer, near the feeder, and at the center) at the end of the experiment. The collected litter samples were stored in the refrigerator at −20°C until further analysis. Litter pH was determined by the method described by Pope and Cherry [13]. Litter moisture concentrations were measured by drying oven at 100°C for 12 hours. Litter nitrogen (N) concentrations were determined using the Kjehldahl method [14]. At the conclusion of the experiment, the FPD incidence was also measured visually using 10 birds randomly selected per pen based on a 6-point scale scoring system [15]: score 0, smooth and no lesion; score 1, discoloration and small injury; score 2, dark papillae and no ulceration; score 3, small ulcer covered by crust; score 4, medium ulcer covered by crust; and score 5, big ulcer covered by crust.
Statistical analysis
All data were tested for normal distribution and outliers with the UNIVARIATE procedure of SAS (SAS Institute Inc., Cary, NC, USA). No outliers were identified. All data except for FPD incidence were normally distributed. Thus, data with normal distribution were analyzed by the MIXED procedure of SAS, whereas data for FPD incidence were analyzed by the GLIMMIX procedure of SAS [16]. The LSMEANS procedure was used to calculate mean values. The orthogonal polynomial contrast test was also performed to determine linear and quadratic effects of increasing Ca concentrations in diets. Significance and tendency for statistical tests were set at p<0.05 and 0.05≤p≤0.10, respectively.
RESULTS
Growth performance including final BW, BWG, FI, G:F, and mortality was not affected by dietary treatments (Table 2). A tendency (linear, p = 0.05) for decreased G:F was observed as dietary Ca concentrations were increased.
As expected, increasing Ca concentrations in low NPP diets containing phytase increased (linear and quadratic, p<0.01) the concentrations of Ca and P in the tibia of growing broiler chickens, but had no effects on tibia ash contents and breaking strength (Table 3). Notably, broiler chickens fed diets containing 4.0 g/kg Ca concentrations had the least (p<0.05) concentrations of Ca and P in the tibia among those fed experimental diets.
Increasing Ca concentrations in low NPP diets containing phytase had no effects on litter quality including pH, moisture, and N contents (Table 4). However, a tendency (quadratic, p = 0.10) for increased FPD incidence was observed as dietary Ca concentrations were increased with the highest FPD incidence being observed for birds fed diets containing 9.0 g/kg Ca.
DISCUSSION
The analyzed concentrations of Ca in diets (5.2, 6.6, 7.4, 8.6, 9.2, or 9.7 g/kg) were greater by about 0.7 to 1.9 g/kg compared with the formulated concentrations of Ca in diets (4.0, 5.0, 6.0, 7.0, 8.0, or 9.0 g/kg). Similar differences between analyzed and formulated concentrations of Ca in diets have been reported in the previous experiments [17,18]. This difference is probably associated not only with possible underestimation of Ca concentrations of ingredients used in the diet formulation but also with the use of calcium carbonate carrier in vitamin and mineral premix used in diet formulation [18].
The observation that growth performance including BW, BWG, FI, and mortality was not affected by dietary treatments agrees with Rousseau et al [19] who reported that increasing Ca concentrations from 3.7 to 7.7 g/kg in diets had no effects on growth performance of growing broiler chickens. Our result indicates that the concentrations of Ca from 4.0 to 9.0 g/kg in low NPP diets containing phytase did not significantly limit growth performance of growing broiler chickens. However, increasing Ca concentrations in diets tended to decrease the G:F. Powell et al [20] also reported a similar decrease in the G:F of broiler chickens fed diets containing high Ca concentrations. However, Rousseau et al [19] showed no significant difference in the G:F of growing broiler chickens fed diets containing 3.7, 5.7, or 7.7 g/kg Ca concentrations. The reason for these variable results among experiments may be associated with the difference in the Ca:NPP ratio in experimental diets. The current NRC recommendation for the Ca:NPP ratio is 2.6:1 (9.0 g/kg Ca:3.5 g/kg NPP) at 3 to 6 weeks of age [1]. However, this ratio has been questionable because of changes in genetic development, management, and raising environment of modern broiler industry. Currently, low NPP diets containing phytase, which is similar to our experimental diets, have been widely used in the broiler industry. In this situation, the optimal ratio for broiler chickens should be adjusted [21]. In the present experiment, the reduction up to 1.3:1 (4.0 g/kg Ca:3.0 g/kg NPP) of Ca:P in low NPP diets containing phytase had no detrimental effects on growth performance of growing broiler chickens.
In contrast to growth performance, however, significantly low Ca and P concentrations in the tibia were observed for growing broiler chickens fed diets containing 4.0 g/kg Ca although there were no differences in tibia ash and breaking strength among treatments. This result indicates that the reduction up to 1.7:1 (5.0 g/kg Ca:3.0 g/kg NPP) of Ca:P in low NPP diets containing phytase may have little negative effects on bone mineralization of growing broiler chickens. However, one should be cautious in considering the current data because the feeding duration of experimental diets in this experiment was only 14 days, which may be too short to impair bone mineralization of growing broiler chickens.
It is suggested that wet litter problems may be exacerbated by high concentrations of Ca in broiler diets because poultry have a limited capacity of reabsorbing Ca in the kidney, leading to a polyuria [7,22]. In the current experiment, however, birds fed low NPP diets containing increasing Ca concentrations from 4.0 to 9.0 g/kg had no effects on litter moisture contents. This result is probably due to the fact that increasing Ca concentrations from 4.0 to 9.0 g/kg in low NPP diets containing phytase did not interrupt renal reabsorption capacity of Ca. In the line with litter moisture content, litter pH and N contents were not affected by increasing Ca concentrations in diets. Therefore, it can be elucidated that dietary Ca concentrations in the range of 4.0 to 9.0 g/kg may have no negative effects on litter pH and N contents.
The FPD has been often related to poor litter quality such as high litter moisture and N contents [8]. However, we observed the highest FPD incidence in growing broiler chickens fed diets containing 9.0 g/kg Ca, which is the current Ca recommendation of NRC [1], despite no differences in litter quality among dietary treatments. The reason for little association between litter quality and FPD incidence as observed in this experiment is not clear; it may be related to the other factors affecting litter quality such as animal conditions, temperature, humidity, bedding materials, and litter microbial population, possibly in relation to different Ca concentrations in diets [8]. However, our result indicates that FPD incidence for growing broiler chickens may be decreased if less than 9.0 g/kg of Ca was included in diets.
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 during 14 days of feeding. 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.
ACKNOWLEDGMENTS
This research was carried out with the support of the Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ01093204), Rural Development Administration, Republic of Korea. This research was also supported by the Chung-Ang University Graduate Research Scholarship in 2016.
Notes
CONFLICT OF INTEREST
We certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.