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J APPL POULT RES 2006. 15:493-501
© 2006 Poultry Science Association
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Research Reports

Effect of High Concentrations of Cholecalciferol on Growth, Bone Mineralization, and Mineral Retention in Broiler Chicks Fed Suboptimal Concentrations of Calcium and Nonphytate Phosphorus

S. V. Rama Rao1, M. V. L. N. Raju, A. K. Panda, G. Shyam Sunder and R. P. Sharma

Project Directorate on Poultry, Indian Council of Agricultural Research, Rajendranagar, Hyderabad 500 030, India

Correspondence: 1 Corresponding author: svramarao1{at}rediffmail.com


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
An experiment was conducted to examine the effects of supplementing high concentrations (200 vs. 1,200, 2,400, and 3,600 ICU/kg) of cholecalciferol (CC) on performance, bone mineralization, and mineral retention in broiler chickens (2 to 42 d of age) fed a basal diet containing suboptimal concentrations of Ca and nonphytate P (NPP; 0.5 and 0.25%, respectively). A reference diet (RD) containing recommended levels of Ca, NPP, and CC was considered as control. Each diet was fed ad libitum to 21 replicates containing 5 birds in each. Body weight gain, feed efficiency, tibia ash, and serum Ca and inorganic P decreased significantly (P < 0.05) in broilers fed suboptimal concentrations of Ca and NPP compared with those fed the RD. The BW gain (2,400 ICU/kg) and feed efficiency, leg abnormality score, and bone mineralization characteristics (3,600 ICU/kg) in broilers fed suboptimal concentrations of Ca and NPP with high concentrations of CC were similar to those fed the RD. The concentrations of Zn, Mn, Fe, and Cu in liver increased significantly (P < 0.05) with increase in concentrations of CC in the basal diet. Based on the results, it is concluded that performance and bone mineralization in broilers could be maintained with suboptimal concentrations of Ca and NPP (0.5 and 0.25%, respectively) and higher concentrations of CC (3,600 ICU/kg) in the diet.

Key Words: cholecalciferol • calcium • nonphytate phosphorus • broiler chicken


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Poor utilization of phytate P (PP) by chickens is causing serious environmental concern due to the excretion of unutilized P and trace minerals from intensive poultry farming. The PP chelates several essential minerals in cereals and oilseed byproducts [1, 2] and inhibits their availability to chicken, resulting in excretion of these minerals into the environment. Increasing the bird’s ability to utilize PP by supplementing exogenous microbial phytase [3] to diets containing suboptimal Ca and P improved bird performance and bone mineralization similar to those fed optimum concentrations of these minerals.

Recommended or excess concentrations of Ca [3, 4, 5], P [6], or both in the diet reduce the utilization of PP in the chicken gut. Utilization of Ca and P can be enhanced when they are fed at suboptimal concentrations by supplementing high concentrations of cholecalciferol (CC) in diet [7, 8]. Because CC is known to enhance Ca utilization, lower concentrations of these minerals may provide the bird’s requirement by the addition of high concentrations of the vitamin in the diet. The suboptimal concentrations of Ca, P, or both also enhance the utilization of PP in chickens [5, 9] by increasing the activity of intestinal phytase [5, 10] and utilization of Ca and P [9, 11, 12]. Because the cost of synthetic CC is lower than that of supplemental P (dicalcium phosphate), reducing P and Ca concentrations with high concentrations of CC may be beneficial for economic and environmental reasons. In the present study, an attempt was made to examine the possibility of maintaining performance, bone mineralization, and mineral retention in liver of broiler chicks fed suboptimal concentrations of Ca and P with high concentrations of CC in the diet.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Birds and Management
Five hundred twenty-five female 1-d-old Cobb 100 broiler chicks [13] were procured from a local hatchery. The chicks were wing-banded on d 1 and randomly distributed to 105 raised-wire floor stainless steel battery brooder pens with 5 birds/pen. Each brooder was fitted with an individual feeder, waterer, and excreta collection tray. Continuous light was provided with incandescent bulbs. Ground corn was provided ad libitum on d 1, followed by the respective experimental diet up to 42 d of age. Uniform vaccination and management practices were followed for all the experimental groups.

Diets
Starter (up to 21 d of age) and finisher (22 to 42 d of age) reference diets (RD) were prepared to contain 2,800 and 2,980 kcal of ME with 23 and 19% CP, respectively (Table 1Go). Calcium and nonphytate P (NPP) concentrations in starter and finisher RD were maintained at 0.9 and 0.8% and 0.45 and 0.4%, respectively; concentrations in the basal diet (BD) were reduced to 0.50 and 0.25%, respectively. The concentrations of energy, protein, and limiting amino acids in starter and finisher basal diets were maintained at par with the RD. The concentrations of Ca and NPP in basal diets were selected based on our previous studies [11, 12], in which concentrations higher than these (0.6% Ca and 0.3% NPP) did not affect the performance and bone mineralization in broilers chicks at 42 d of age. The BD was supplemented with synthetic CC [14] at 200, 1,200, 2,400, and 3,600 ICU/kg. High concentrations of CC were tested to determine the benefits of the vitamin on utilization of Ca and NPP when they were fed at suboptimal concentrations in the diet. The CC level in the RD was maintained at 200 ICU/kg. To ensure proper mixing of crystalline CC in diets, the vitamin was dissolved in 100 mL of propylene glycol-ethanol solution (95 mL of propylene glycol and 5 mL of ethanol). A separate premix of CC was prepared by mixing the above solution with finely ground corn and added to the respective experimental diet. The concentrations of oyster shell powder, dicalcium phosphate, and corn were adjusted to provide the desired concentrations of Ca and NPP in diets. Each experimental diet was allotted to 21 battery brooder pens (replicates) containing 5 birds in each. Diets were randomly allotted to pens by following the completely randomized design.


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  		Table 1. Ingredient and nutrient composition (%) of reference and basal diets
 
Analysis of Biological Samples and Feed Ingredients
Feed ingredients were analyzed for CP, total ash, Ca, total P [15], and PP [16]. The difference between total P and PP was considered as NPP. Liver samples were analyzed for Zn, Mn, Fe, and Cu with an atomic absorption spectrophotometer [17]. Each nutrient was analyzed in quadruplicate. Blood samples were analyzed for Ca, inorganic P (iP) [18], and activity of alkaline phosphatase using diagnostic kits [19].

Traits Measured
Body weight gain, feed intake, and leg abnormality score (LAS) [20] were recorded at weekly intervals. The degree of leg abnormality was scored as 1 = normal hock joint; 2 = slight swelling of the hock joint; 3 = marked swelling of the joint; 4 = marked swelling of the joint and slight slipping of the Achilles tendon; and 5 = marked swelling and complete slipping of the tendon. Two to three milliliters of blood was drawn from the brachial vein from 1 bird per replicate at 21 and 42 d of age. Sera samples were analyzed for Ca, iP, and activity of alkaline phosphatase. One bird representing the mean value of the replicate was randomly selected and killed by cervical dislocation at 42 d of age. Both tibias were freed of soft tissue and dried at 100°C for 3 h and soaked in petroleum ether for 48 h. Thirty dried bone samples (both tibia of 15 birds) were used to measure bone length, weight, and bone ash content, considering each bone as an individual unit. Bones were ashed at 600 ± 20°C for 4 h in a microwave muffle furnace [21]. Liver samples were dried and ashed initially in perchloric acid, followed by hydrochloric acid. The digested samples of liver were analyzed for Zn, Fe, Mn, and Cu. The experiment was conducted by following the guidelines of the Animal Ethical Committee of India.

Statistical Analysis
The data were analyzed with 1-way ANOVA [22], and the treatment means were compared with Duncan’s multiple range test [23]. The requirement of CC in broilers fed diets containing suboptimal concentrations of Ca and NPP for different characteristics was predicted with Y = a + bx + cx2 + dx3 or lower order. When a characteristic was found significant, the requirement of CC for the parameter was predicted using the specific equation either for the maximum output or the output equivalent to that of the RD-fed group.


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Ca and P Contents in Feed Ingredients
Analyzed concentrations of Ca, total P, and PP in corn, soybean meal, and deoiled rice bran were 0.22, 0.31, and 0.06%; 0.067, 0.058, and 1.19%; and 0.046, 0.386, and 1.01%, respectively. Similarly, dicalcium phosphate contained 24.67% Ca and 16.63% P, whereas shell grit contained 38.03% Ca.

BW Gain, Feed Efficiency, and LAS
Body weight gain, feed efficiency (weight gain/feed intake), LAS, Ca, and iP concentrations and the activity of alkaline phosphates in serum were significantly influenced by the treatments used at both 21 and 42 d of age, except the LAS (P < 0.05) at 21 d of age (Table 2Go). The weight gain at 21 and 42 d of age was significantly (P < 0.05) depressed by feeding CC at 200 ICU/kg compared with those fed RD. Supplementing high concentrations of CC (2,400 ICU/kg) to BD significantly improved weight gain, similar to those fed the RD. The predicted requirement of CC for maximum BW gain at 21 d of age was 3,182 ICU/kg (Table 3Go). At 42 d of age, growth showed progressive increase with the CC level up to 3,600 ICU/kg of diet, but the predicted requirement of CC for obtaining the BW gain observed in the RD fed group (Table 2Go) was 3,424 ICU/kg of diet (Table 3Go).


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  		Table 2. Performance, leg abnormality score (LAS), and serum biochemical profile in broilers at 21 and 42 d of age fed different concentrations of cholecalciferol (CC) in basal diet (BD) containing suboptimal concentrations of Ca and NPP
 

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  		Table 3. Regression coefficients, correlations and predicted cholecalciferol (CC) requirements (ICU/kg) for maximum performance of broiler chicks fed suboptimal concentrations of Ca and NPP1
 
At 21 d of age, the feed efficiency depressed significantly (P < 0.05) in broilers fed BD compared with those fed the RD and was not affected by supplementing higher concentrations of CC to the BD. However, at 42 d of age, the feed efficiency of broilers fed BD with 3,600 ICU of CC/kg was similar to those fed the RD, whereas the feed efficiency in other groups was poorer than that of the RD-fed broilers.

The LAS was not affected at 21 d of age, whereas at 42 d of age, the leg abnormality increased significantly (P < 0.05) in broilers fed the BD with 200, 1,200, and 2,400 ICU of CC/kg compared with those maintained on the RD. However, the LAS in groups fed BD with 3,600 ICU of CC was similar to those fed the RD.

Based on the data, the predicted requirement of CC for BW gain (3,182 and 3,424 ICU/kg of diet during the starter and finisher phases, respectively) and bone ash (3,485 ICU/kg) were considerably higher than the concentrations (200 ICU/kg) recommended by the NRC [24] or those of several authors (400 to 1,000 ICU/kg) [25, 26, 27, 28]. The lower concentrations recommended by these authors might be due to the adequate concentrations of Ca and P (about 1.0 and 0.7%, respectively) used in the basal diets. It has been well established that at optimum concentrations of Ca and NPP, the dietary requirement of CC is reduced [8].

The feed efficiency and LAS at 42 d of age in broilers fed BD with 3,600 ICU of CC/kg were comparable to those fed RD. Thus, the results suggest higher requirements of CC for broiler chicks fed suboptimal concentrations of Ca and NPP. That is, broiler performance could be maintained by feeding diets with higher concentrations of CC (3,600 ICU/kg) in diets containing suboptimal concentrations of Ca and NPP (BD).

The predicted requirement of CC for maximum tibia ash content (3,485 ICU/kg) was similar to that of BW gain (3,182 and 3,424 ICU/kg of starter and finisher diets, respectively). Further, the 42-d LAS of broilers fed the highest level of CC (3,600 ICU/kg) was similar to that of RD, which contained the recommended concentrations of Ca and NPP (Table 2Go). Literature also suggests higher requirements of CC at suboptimal concentrations of dietary Ca and P for optimum BW gain [7, 9, 29, 30, 31] and bone mineralization [7, 32]. The beneficial effects of high CC concentrations at suboptimal concentrations of Ca and NPP might be due to its role in phytate utilization. Higher concentrations of CC in the diet are known to stimulate hydrolysis of phytate [7, 9, 33, 34]. Cholecalciferol improves Ca absorption through the gut, which in turn facilitates solubility of the phytin-mineral complex, thereby improving the accessibility of the molecule for hydrolysis [35, 36].

Serum Biochemical Profile
The activity of alkaline phosphatase increased significantly (P < 0.05) in groups fed CC at 200 ICU/kg compared with those fed the RD at both 21 and 42 d of age (Table 2Go). Although supplementation of higher concentrations of CC (3,600 ICU/kg) to BD reduced the enzyme activity, it was still higher than that of RD. The concentration of Ca and iP in the serum was significantly (P < 0.05) depressed in broilers fed BD compared with those fed the RD. Concentrations of these minerals in the serum increased progressively with the level of CC supplementation to BD at both 21 and 42 d of age. The concentrations of serum Ca and iP in broilers fed BD supplemented with 3,600 ICU of CC were similar to those of the chicks fed the RD.

Increased concentrations of Ca and iP in the serum of broilers fed suboptimal concentrations of Ca and NPP with increased CC level in BD also suggest the beneficial effects of higher CC concentrations on the utilization of dietary Ca and P in chicken. Lofton and Soares [25] also reported increased serum Ca concentrations with increased dietary CC concentration. Increased utilization of Ca and PP at higher concentrations of CC in the diet [7, 9, 33] may be responsible for the increase in serum P concentration. Increased activity of alkaline phosphatase in the serum of broilers fed the BD (CC at 200 ICU/kg) suggests Ca insufficiency, which was evident by reduced concentrations of Ca and iP in the serum (Table 2Go) and increased LAS at 42 d of age. Increasing CC concentrations in BD improved serum Ca and iP concentrations and concomitantly reduced the LAS at 42 d of age.

Tibia Mineralization Characteristics
Bone mineralization characteristics (i.e., tibia weight, length and total ash content) as affected by the concentrations of Ca, NPP, and CC in diet are presented in Table 4Go. Tibia weight decreased significantly (P < 0.05) in broilers fed CC at 200 ICU/kg compared with those fed the RD. Supplementing 2,400 ICU of CC/kg to BD significantly increased the bone weight compared with CC at 200 ICU/kg, but the weight was lower compared with those fed the RD. The tibia length was significantly (P < 0.05) higher in groups fed BD, irrespective of the level of CC supplementation compared with those fed the RD.


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  		Table 4. Tibia mineralization in broilers (42 d of age) fed different concentrations of cholecalciferol (CC) in basal diet (BD) containing suboptimal concentrations of Ca and NPP
 
Tibia ash content was reduced significantly (P < 0.05) in broilers fed suboptimal concentrations of Ca and NPP with 200 ICU of CC/kg compared with those fed the RD (Table 4Go). The bone ash content was increased (P < 0.05) progressively with increased concentrations of CC in BD, and the ash content in birds fed 3,600 ICU of CC/kg was statistically similar (P < 0.05) to those fed the RD. The predicted requirement of CC for maximum tibia ash content was 3,485 ICU/kg of diet.

Trace Mineral Content in Liver
Concentrations of trace minerals in liver were reduced significantly (P < 0.05) in chicks fed CC at 200 ICU/kg compared with those fed RD (Table 5Go). The concentrations of Mn, Fe, and Cu in liver were significantly higher in broilers fed BD supplemented with 2,400 ICU of CC compared with those fed the RD, whereas the Zn retention was higher at 3,600 ICU of CC compared with those fed the RD.


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  		Table 5. Retention of trace minerals in liver (mg/kg) of broilers fed different concentrations of cholecalciferol (CC) in diet (BD) containing suboptimal concentrations of Ca and nonphytate P (NPP)
 
Increased retention of trace minerals in liver, as sequel to increased CC level in the diet, may be due to better utilization of the trace minerals with increased PP hydrolysis [7, 9, 33, 34]. This hypothesis is also supported by increased concentrations of TP, Ca, and trace minerals in excreta and increased deposition of trace minerals in liver (Table 5Go). Enhanced utilization of PP might have liberated bound P (PP), Ca, and trace minerals and facilitated their utilization and retention in liver. Increased deposition of minerals (Ca, P, Zn, Mn) in tibia due to enhanced utilization of PP in broilers was also reported in the literature [29, 37].


   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 

  1. Body weight gain, feed efficiency, Ca, and iP concentrations in serum and tibia ash content decreased significantly in broilers fed suboptimal concentrations of Ca and NPP (0.5% and 0.25%, respectively) compared with those fed the recommended concentrations of these minerals in diet.
  2. Body weight gain, feed efficiency, leg abnormality score, and bone mineralization characteristics in broilers fed the suboptimal concentrations of Ca and NPP with high concentrations of CC (3,600 ICU/kg) were similar to those fed the recommended levels of Ca, P, and CC in diet.
  3. Retention of the trace minerals (Mn, Fe, Zn, and Cu) in liver increased significantly with increased concentrations of CC in diets containing suboptimal concentrations of Ca and NPP.
  4. Reducing the concentrations of supplemental NPP from 0.45% and 0.4% to 0.25% and Ca from 0.9 and 0.8% to 0.5% during starter and finisher phases, respectively, with higher supplemental concentrations of CC reduced the feed cost by about $0.13/bird up to 42 d of age.
  5. Based on the results, it is concluded that performance and bone mineralization in broilers could be maintained when feeding suboptimal concentrations of Ca and NPP (0.5 and 0.25%, respectively) with a higher level of CC (3,600 ICU/kg).


   ACKNOWLEDGMENTS
 
We thank to the Indian Council of Agricultural Research for financing this research project under the Young Scientist Awards Scheme. The support given by O. Krishna Murthy, K. Radhika, and S. Sasibindu for their help in the farm and lab work is acknowledged.


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

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