Comparison of Cholecalciferol and 25-Hydroxycholecalciferol in Broiler Diets Designed to Minimize Phosphorus Excretion 1

Transcription

1 2005 Poultry Science Association, Inc. Comparison of Cholecalciferol and 25-Hydroxycholecalciferol in Broiler Diets Designed to Minimize Phosphorus Excretion 1 C. A. Fritts 2 and P. W. Waldroup 3 Poultry Science Department, University of Arkansas, Fayetteville, Arkansas Primary Audience: Nutritionists, Veterinarians, Production Managers, Researchers SUMMARY A study was conducted to evaluate 2 phosphorus regimes (NRC; modified), using diets supplemented with 1,000, 2,000, or 4,000 IU/kg of cholecalciferol (VIT-D3) or the equivalent amount of 25-hydroxycholecalciferol (25-OH-D3). Each treatment was assigned to 4 pens of 25 male broilers of a commercial strain grown in an open-sided house with sidewall curtains. At 21, 42, and 49 d BW and feed conversion (FCR) were determined. At 49 d, 5 birds per pen were killed to evaluate tibia ash of the right leg and incidence and severity of tibial dyschondroplasia (TD) of the left tibia. All remaining birds were processed at a pilot processing plant with agitated chilling and automatic evisceration to determine incidence of broken bones. No differences in BW were observed at 21 d due to dietary treatments. At 42 d, the BW of birds fed 4,000 IU/kg of vitamin D was significantly greater than birds fed 1,000 or 2,000 IU/kg; at 49 d the BW of birds fed 4,000 IU/kg of vitamin D was significantly better than that of birds fed 1,000 IU/kg with the BW of birds fed 2,000 IU/kg intermediate between these 2 levels. No significant differences in BW were observed at any age between source of vitamin D, phosphorus program used, or any interaction among or between vitamin D source, level, or phosphorus program. There were no significant differences observed for FCR and mortality at any age period or for tibia ash at 49 d. Birds fed 25-OH-D3 had a significantly higher severity of TD than birds fed VIT-D3, with no effect of vitamin D level and phosphorus program. Birds fed the modified phosphorus diet in combination with 2,000 IU/kg vitamin D had significantly lower incidence of TD than birds fed the NRC phosphorus diet with the same level of vitamin D. There were no significant differences among treatments for the number of broken bones during automatic evisceration in a pilot processing plant. Key words: cholecalciferol, 25-hydroxycholecalciferol, vitamin D, broiler, phosphorus 2005 J. Appl. Poult. Res. 14: DESCRIPTION OF PROBLEM Poultry diets are formulated to provide a margin of safety for phosphorus to ensure an adequate skeletal system for the rapidly growing bird. A significant amount of phosphorus in the diet is in the form of phytate phosphorus, an organically bound form that chickens cannot 1 Published with the approval of the Director, Agricultural Experiment Station, Fayetteville, AR Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the University of Arkansas and does not imply its approval to the exclusion of other products that may be suitable. 2 Current address: Poultry Science Department, Mississippi State University, Mississippi State, MS To whom correspondence should be addressed: waldroup@uark.edu.

2 FRITTS AND WALDROUP: VITAMIN D SOURCES AND REDUCED PHOSPHORUS 157 readily digest [1, 2]. Research has shown that supplementation of poultry diets with phytase can allow reduction of overall dietary phosphorus levels by increasing the ability of the chick to use a portion of the phytate-bound phosphorus [3, 4, 5, 6, 7, 8, 9, 10, 11]. Because of environmental concerns, greater pressure is being placed upon the poultry industry to minimize phosphorus in poultry excreta. Therefore, reduction of dietary phosphorus is 1 approach to minimizing adverse effects of the poultry industry on the environment. Vitamin D is needed for proper absorption of calcium [12, 13, 14] and influences the absorption of phosphorus. The NRC [15] recommends a minimum of 200 IU/kg of vitamin D, and commercial diets are typically fortified at 10 to 20 times above this level [16]. Vitamin D in excess of NRC recommendations has been shown to reduce the incidence of rickets and tibial dyschondroplasia (TD), which are still observed in commercial situations [17, 18, 19, 20]. Vitamin D has typically been supplied to broilers in the form of cholecalciferol (VIT-D3), which must undergo change in the liver to become 25- hydroxycholecalciferol (25-OH-D3) and in the kidney to become 1,25-dihydroxycholecalciferol, considered to be the active metabolite of vitamin D [21]. In 1995, 25-OH-D3 was given generally recognized as safe status for use as a vitamin source in poultry [22]. Compared with comparable levels of VIT-D3, this metabolite has been shown under certain conditions to improve BW gain, feed efficiency, bone ash, and breast meat yield and to reduce the incidence of rickets and TD [17, 23, 24, 25, 26, 27, 28, 29, 30]. In a previous study in our laboratory [31], using calcium and phosphorus levels suggested by NRC [15], we demonstrated that chicks fed 25-OH-D3 as a source of vitamin D had improved BW, a greater percentage of bone ash, and a lower incidence and severity of TD than chicks fed similar levels of vitamin D from VIT- D3. Much of this difference was due to improvements at low levels of vitamin D supplementation. Recent research has suggested that phosphorus use of the chick may be improved by increasing levels of cholecalciferol or by utilizing other vitamin D isomers in the diet. Applegate et al. [32] found that supplementation of diets with 25-OH-D3 at 210 µg/kg (8,400 IU/ kg) provided an additional 0.065% of dietary phosphorus from phytate as compared with cholecalciferol. Angel et al. [33] reported that 70 µg/ kg (2,800 IU/kg) of 25-OH-D3 spared 0.035% phosphorus when fed in phytase-supplemented, low nonphytate phosphorus diets. Various isomers of vitamin D fed in conjunction with phytase have been shown to improve intestinal phytase or to act with microbial phytase to improve phosphorus use [8, 9, 11, 34, 35, 36, 37, 38]. However, much of this research has been conducted using vitamin D isomers not typically fed to broiler chicks, such as 1,25-(OH) 2 -D 3 and 1α-hydroxylated cholecalciferol. As a means of reducing phosphorus excretion, we have suggested a modified phosphorus feeding program with phytase supplementation to allow for adequate skeletal growth in the starter diet followed by markedly reduced phosphorus levels in grower and finisher diets [39, 40, 41, 42]. This modified phosphorus program reduced phosphorus excretion and maintained livability and tibia ash at lower dietary levels of nonphytate phosphorus. In these cited studies, cholecalciferol was used as the source of vitamin D. The objective of the present study was to compare sources of vitamin D when fed in conjunction with phytase-supplemented diets with reduced phosphorus levels. MATERIALS AND METHODS All diets were formulated to meet or exceed NRC [15] recommendations for essential amino acids in starter (0 to 21 d), grower (21 to 42 d), and finisher (42 to 49 d) feeding periods. One series (NRC) was formulated to provide NRC [15] recommendations for calcium and nonphytate P (NPP). By adjusting the level of dicalcium phosphate, ground limestone, and washed builders sand in this diet, a modified series was prepared that provided for early skeletal development followed by markedly reduced levels of NPP in grower and finisher diets (0.40, 0.20, and 0.10% NPP in starter, grower, and finisher diets, respectively). Calcium levels in the modified diets were 0.70, 0.60, and 0.50% for starter, grower, and finisher periods, respectively. All diets in this series were supplemented with 1,000 phytase units (FTU)/kg of phytase [43]. The composition of the diets is shown in Table 1.

3 158 JAPR: Research Report TABLE 1. Composition (g/kg) and calculated nutrient content of diets for broilers fed diets with different levels and sources of vitamin D and phosphorus feeding levels Ingredient 0 to 3 wk 3 to 6 wk 6 to 7 wk Yellow corn Soybean meal (47.5%) Poultry oil DL-Met (98%) Iodized salt BMD Coban Vitamin premix Choline Cl (60%) L-Lys HCl (98%) Trace mineral mix L-Thr Variable Total 1, , , Calculated analysis ME, kcal/kg 3, , , CP Met, % Lys, % Thr, % Met + Cys, % Chloride, % Sodium, % Alpharma, Inc., Ft. Lee, NJ. 2 Elanco Animal Health division of Eli Lilly and Co., Indianapolis, IN. 3 Provides per kilogram of diet: vitamin A, 7,714 IU; vitamin E, IU; vitamin B 12, mg; riboflavin, 6.6 mg; niacin, 39 mg; pantothenic acid, 10 mg; menadione, 1.5 mg; folic acid, 0.9 mg; thiamin, 1.54 mg; pyridoxine, 2.76 mg; D-biotin, mg; ethoxyquin, 125 mg; Se, 0.1 mg. 4 Provides 1,040 mg choline per kilogram of diet. 5 Provides per kilogram of diet: Mn (from MnSO 4 H 2 O) 100 mg; Zn (from ZnSO 4 7H 2 O) 100 mg; Fe (from FeSO 4 7H 2 O) 50 mg; Cu (from CuSO 4 5H 2 O) 10 mg; I from Ca(IO 3 ) 2 H 2 O), 1 mg. 6 Variable amounts of dicalcium phosphate, ground limestone, and washed builders sand. Within each phosphorus series, diets were supplemented with 1,000, 2,000, or 4,000 IU/kg of cholecalciferol (VIT-D3) [44] or equivalent amounts of 25-hydroxycholecalciferol (25-OH- D3) [45] based on the conversion of µg to 1 IU [15]. According to an industry survey of commercial broiler producers [46], the average level of vitamin D supplementation in broiler starter diets in the US commercial poultry industry was 2,819 IU/kg with the low 25% of producers adding 1,988 IU/kg and the top 25% of producers adding 4,030 IU/kg. The vitamin D sources were premixed in finely ground corn meal prior to addition to the diets to enhance mixing. The combination of 2 phosphorus regimes, 2 vitamin D sources, each fed at 3 levels, resulted in a factorial for a total of 12 experimental treatments, with each treatment assigned to 4 replicate pens of male broiler chicks. Samples of all feeds were assayed for calcium, total phosphorus, and vitamin D activity by commercial laboratories specializing in these analyses. Phytase-supplemented diets were analyzed for phytase activity in the laboratory of a major supplier of phytase. Day-old male chicks of a commercial strain [47] were obtained from a local hatchery where they had been vaccinated in ovo for Marek s disease and had received vaccinations for Newcastle disease and infectious bronchitis posthatch via a coarse spray. Twenty-five birds were placed in each of 48 pens in a steel-truss poultry house of commercial design. The house had a 1-m sidewall curtain [48] with an ultraviolet inhibition rating of 70% that was kept closed at all times during the study. There were 2 outside rows of 12 pens each and 2 inside rows of 12 pens each. Inside and outside pens served as

4 FRITTS AND WALDROUP: VITAMIN D SOURCES AND REDUCED PHOSPHORUS 159 blocks in the experimental design. Each pen contained 1 tube-type feeder and 1 bell-type automatic water fount. Birds were provided with ad libitum access to feed and water with 23L:1D. One 9-W fluorescent light suspended 198 cm over the litter provided supplemental light in each pen. House temperature and airflow were controlled by thermostatically controlled brooder stoves and ventilation fans. Care and management of the birds followed accepted guidelines [49]. The study began on June 18, 2002, and concluded August 6, 2002; thus, high summer temperatures were encountered during the study. Pen body weights were obtained at 21, 42, and 49 d of age. Feed consumption was determined for the same time periods. Birds were checked twice daily; weight of dead birds was used to adjust for feed consumption. At 49 d, 5 birds per pen were killed to evaluate tibia ash and incidence and severity of TD. The left tibia was analyzed for ash content as described by AOAC [50], and the right tibia scored for TD using the scoring system of Edwards and Veltmann [51]. Scores in this system ranged from 0 (no apparent TD) to 3 (most severe). All remaining birds were processed in a pilot processing plant with automatic evisceration and agitated chilling. Feed but not water was withheld for 12 h before placing the birds in coops and transporting approximately 2 km to the processing plant where they were processed as described [52]. Following processing, the incidence of broken wings, legs, and rib cage was determined. Pen means were the experimental unit for all data. Data were subjected to ANOVA as a factorial arrangement of treatments with vitamin D source, vitamin D level, and phosphorus regimes as the main effects; all possible interactions among and between the main effects were evaluated using the general linear model procedure of SAS [53]. All percentage data other than mortality were transformed to arc sine percentage prior to analysis; data are shown as natural numbers. Mortality data were transformed to n + 1 prior to analysis. Significant differences among or between means were separated by repeated t-tests using the least squares means option of SAS. Statements of significance are based on P 0.05 unless otherwise noted. RESULTS AND DISCUSSION Calculated and analyzed levels of VIT-D3, 25-OH-D3, phytase, calcium, and total phosphorus in the experimental diets are shown in Table 2. In general there was good agreement between calculated and analyzed levels for all of the test articles in the various research diets. Calcium and total phosphorus analyses were also within expected ranges. Only 1 significant interaction was observed upon statistical analysis; thus, only main effects will be shown in tables with the lone interaction shown in Figure 1. Body weight was not significantly affected by source of vitamin D or by phosphorus feeding program at any age interval (Table 3). The level of vitamin D had no significant effect at 21 d of age; however, at 42 and 49 d of age increasing the level of vitamin D generally resulted in a significant increase in BW. At 42 d of age, birds fed diets supplemented with 4,000 IU/kg of vitamin D had significantly greater BW than those fed diets with 1,000 or 2,000 IU/kg; at 49 d the BW of birds fed 4,000 IU/kg was significantly greater than that of birds fed 1,000 IU/kg, with the BW of those fed 2,000 IU/kg being intermediate between these 2 levels. There were no significant interactions between or among main effects for BW at any age; these data are not shown for brevity. There were no significant main effects or interactions of main effects on feed efficiency or mortality at any time during the study. Tibia ash content was not significantly affected by source of vitamin D, level of vitamin D, phosphorus feeding program, or any interaction among or between these main effects (Table 4). This further supports the use of the modified phosphorus feeding program as a means of reducing phosphorus excretion. The incidence of TD (percentage of birds having TD scores greater than zero) was not significantly influenced by source or level of vitamin D or phosphorus program at 49 d (Table 4). However, there was a significant interaction of vitamin D level and phosphorus level on the incidence of TD (Figure 1). No significant differences in incidence of TD were observed between birds fed the NRC or modified feeding programs when the birds were fed either 1,000 or 4,000 IU/kg of vitamin D; when the modified phosphorus

5 160 JAPR: Research Report TABLE 2. Calculated (C) and analyzed (A) levels (mean ± SD) of cholecalciferol, 25-hydroxycholecalciferol, phytase, calcium, and total phosphorus in experimental diets Product assayed Unit Feeding period C A C A C A Cholecalciferol 1 IU/kg 0 21 d 1,000 1,078 ± 171 2,000 2,111 ± 282 4,000 3,650 ± 311 IU/kg d 1,000 1,120 ± 153 2,000 2,188 ± 292 4,000 4,125 ± 325 IU/kg d 1, ± 143 2,000 2,068 ± 278 4,000 4,056 ± Hydroxycholecalciferol 2 µg/kg 0 21 d ± ± ± 8.9 µg/kg d ± ± ± 7.6 µg/kg d ± ± ± 9.7 Phytase 3 FTU/kg d 1, ± 27 FTU/kg d 1,000 1,050 ± 34 FTU/kg d 1,000 1,082 ± 22 Calcium 5 % 0 21 d (NRC) ± 0.07 % d (NRC) ± 0.03 % d (NRC) ± 0.02 % 0 21 d (MOD) ± 0.02 % d (MOD) ± 0.02 % d (MOD) ± 0.02 Total phosphorus 5 % 0 21 d (NRC) ± 0.02 % d (NRC) ± 0.02 % d (NRC) ± 0.01 % 0 21 d (MOD) ± 0.02 % d (MOD) ± 0.02 % d (MOD) ± Assays conducted by Roche Vitamins Inc., Parsippany, NJ. 2 Assays conducted by Monsanto Animal Nutrition, Naperville, IL. 3 Assays conducted by BASF Corporation, Mount Olive, NJ. 4 FTU = phytase unit. 5 Assays conducted by Agricultural Diagnostic Laboratory, University of Arkansas, Fayetteville, AR, using inductively coupled plasma-atomic spectroscopy following HNO3 digestion. NRC = NRC [15] recommended levels; MOD = 0.40, 0.20, and 0.10% nonphytate phosphorus fed in combination with 1,000 phytase units (FTU)/kg of phytase for 0 to 21 d, 21 to 42 d, and 42 to 49 d, respectively.

6 FRITTS AND WALDROUP: VITAMIN D SOURCES AND REDUCED PHOSPHORUS 161 FIGURE 1. Interaction of phosphorus feeding program and level of vitamin D on incidence of tibial dyschondroplasia (TD) in 49-d-old male broilers. The incidence of TD is based on percentage of birds with TD score greater than 0 (no apparent TD) based on system of Edwards and Veltmann [51]. The NRC feeding program is based on nonphytate phosphorus recommendations of NRC [15]. The modified (MOD) program consists of 0.40, 0.20, and 0.10% nonphytate phosphorus fed in combination with 1,000 phytase units (FTU)/kg of phytase for 0 to 21 d, 21 to 42 d, and 42 to 49 d, respectively. The levels of vitamin D are means of 2 sources of vitamin D (cholecalciferol and 25-OH-cholecalciferol). diet was fed to birds in combination with 2,000 IU/kg of vitamin D, a significantly lower incidence of TD was observed compared with those fed the NRC diet. The severity of TD (percentage of birds having a TD score of 3) was significantly affected by the source of vitamin D but not by level of vitamin D or phosphorus feeding program (Table 4). The severity of TD in birds fed diets containing 25-OH-D3 was significantly higher than birds fed diets with VIT-D3. As there was a considerable variation associated with this measurement (CV of 89.04), the significance of this effect is debatable, as it was not observed in our previous study dealing with these 2 sources of vitamin D [31]. No significant interactions were observed between or among main effects for severity of TD; data are not presented for brevity. Other reports on the effects of vitamin D sources on incidence or severity of TD have been variable. Edwards [19] reported that the addition of 25-OH-D3 to a diet containing no VIT-D3 caused higher bone ash and lower incidence of TD in the absence or presence of disulfiram, a compound known to increase the development of TD. Rennie and Whitehead [54] observed that replacing 75 µg/kg of VIT-D3 with the same weight of 25-OH-D3 significantly reduced the incidence of TD from 65 to 10%. Roberson [55] reported that 25-OH-D3 did not prevent TD in commercial broiler chicks raised in battery brooder cages when fed at levels as high as 250 µ/kg. Bar et al. [56] reported that the effects of VIT-D3 and 25-OH-D3 in the severity or frequency of TD were similar. Led-

7 162 JAPR: Research Report TABLE 3. Effects of source and level of vitamin D and phosphorus feeding program on BW, feed conversion, and mortality of male broilers BW (g) Feed:gain ratio Mortality (%) Dietary treatment n 1 21 d 42 d 49 d 0 21 d 0 42 d 0 49 d 0 21 d 0 42 d 0 49 d Source of vitamin D 2 VIT-D ,392 2, OH-D ,414 2, Level of vitamin D (IU/kg) 3 1, ,355 b 2,836 b , ,385 b 2,883 ab , ,469 a 2,963 a Phosphorus feeding program 4 NRC ,874 2, MOD ,914 2, Source of variation Source of vitamin D (source) Level of vitamin D (level) Phosphorus program (program) Source level Source program Level program Source level program SEM P > F a,b Within columns, means with common superscripts do not differ significantly (P 0.05). 1 Number of replicate pens containing 25 male broilers. 2 VIT-D3 = cholecalciferol; 25-OH-D3 = 25-hydroxycholecalciferol. 3 Levels of 25-hydroxycholecalciferol were calculated to be equal to similar levels of cholecalciferol based on conversion of µg to1iu. 4 NRC = NRC [15] recommended levels; MOD = 0.40, 0.20, and 0.10% nonphytate phosphorus fed in combination with 1,000 phytase units (FTU)/kg of phytase for 0 to 21 d, 21 to 42 d, and 42 to 49 d, respectively.

8 FRITTS AND WALDROUP: VITAMIN D SOURCES AND REDUCED PHOSPHORUS 163 TABLE 4. Effect of source and level of dietary vitamin D and phosphorus feeding program on tibia ash and on incidence and severity of tibial dyschondroplasia (TD) in 49-d-old male broilers Tibia ash Incidence Severity Dietary treatment n 1 (%) 2 of TD (%) 3 of TD (%) 4 Source of vitamin D 5 VIT-D b 25-OH-D a Level of vitamin D (IU/kg) 6 1, , , Phosphorus feeding program 7 NRC MOD P > F Source of variation Source of vitamin D (source) Level of vitamin D (level) Phosphorus program (program) Source level Source program Level program Source level program SEM CV a,b Within columns, means with common superscripts do not differ significantly (P 0.05). 1 Number of replicate pens with 5 males sampled. 2 Percentage ash in dry, fat-free bone. 3 Percentage with TD score greater than 0 (no apparent TD) based on system of Edwards and Veltmann [51]. 4 Percentage with TD score of 3 (most severe) based on system of Edwards and Veltmann [51]. 5 VIT-D3 = cholecalciferol; 25-OH-D3 = 25-hydroxycholecalciferol. 6 Levels of 25-hydroxycholecalciferol were calculated to be equal to similar levels of cholecalciferol based on conversion of µg to1iu. 7 NRC = NRC [15] recommended levels; MOD = 0.40, 0.20, and 0.10% nonphytate phosphorus fed in combination with 1,000 phytase units (FTU)/kg of phytase for 0 to 21 d, 21 to 42 d, and 42 to 49 d, respectively. waba and Roberson [57] reported that the effectiveness of 25-OH-D3 to reduce the incidence of TD in young broilers was higher when the dietary calcium level was below 0.85%. Zhang et al. [58] reported that the addition of 25-OH- D3 decreased the incidence of TD in a genetic line selected for low incidence of TD but not in a line selected for high incidence of TD. It has been suggested that the development of TD in chicks selected for high incidence of TD is associated with a subnormal activity to metabolize vitamin D [59]. Both nutritionists and processing plant managers are concerned as to whether reducing the phosphorus level in broiler diets will weaken the skeletal system, increasing the number of broken bones during processing. All remaining birds at the end of the trial were processed in a pilot processing plant. The number of broken legs, wings, and rib cage observed after automatic evisceration and agitated chilling are shown in Table 5. No significant differences were observed among birds fed the different sources or levels of vitamin D or phosphorus program, with no significant interactions among or between the main effects. This trial was conducted to examine both VIT-D3 and 25-OH-D3 fed to broilers at levels typically seen in the commercial industry when fed in conjunction with phytase-supplemented diets with reduced phosphorus levels. When birds were fed either the VIT-D3 or 25-OH-D3 at typical commercial industry levels, it was not surprising to see the same results for live performance as was observed in a previous trial in our laboratory [31]. Birds fed the modified phospho-

9 164 JAPR: Research Report TABLE 5. Effect of source and level of dietary vitamin D and phosphorus feeding program on carcass bone breakage in 49-d-old male broilers after automated evisceration and agitated chilling in a pilot processing plant Broken bones (%) 2 Dietary treatment n 1 Wings Legs Ribs Total Source of vitamin D 3 VIT-D OH-D Level of vitamin D (IU/kg) 4 1, , , Phosphorus feeding program 5 NRC MOD P > F Source of variation Source of vitamin D (source) Level of vitamin D (level) Phosphorus program (program) Source level Source program Level program Source level program SEM Number of birds evaluated. 2 The same bird could have bone wings or legs broken; this was considered to be 2 separate incidences. 3 VIT-D3 = cholecalciferol; 25-OH-D3 = 25-hydroxycholecalciferol. 4 Levels of 25-hydroxycholecalciferol were calculated to be equal to similar levels of cholecalciferol based on conversion of µg to1iu. 5 NRC = NRC [15] recommended levels; MOD = 0.40, 0.20, and 0.10% nonphytate phosphorus fed in combination with 1,000 phytase units (FTU)/kg of phytase for 0 to 21 d, 21 to 42 d, and 42 to 49 d, respectively. rus program supplemented with phytase did not differ significantly in live performance compared with birds fed the NRC phosphorus diet, as demonstrated previously by Waldroup et al. [39] and Yan et al. [40, 41, 42]. In addition, no differences were observed for bone development (tibia ash, bone breakage) in broilers fed the 2 phosphorus feeding programs. Although a number of studies have shown superior performance of broilers fed diets supplemented with 25-OH-D3 in place of, or in combination with, VIT-D3 [17, 19, 20, 25, 28, 30, 54, 58], these studies typically use supple- mental vitamin D levels far lower than normally used in commercial broiler diets. In the present study, using vitamin D levels typically used by the poultry industry, few differences were observed between birds fed the 2 vitamin D sources. However, use of 25-OH-D3 may allow for supplementation with lower levels of vitamin D or may provide a greater margin of safety under stress conditions, as our previous study [31] demonstrated greater efficacy of this product at lower levels of supplementation. CONCLUSIONS AND APPLICATIONS 1. Significant improvement in BW was observed in chicks fed 4,000 IU/kg of vitamin D at 42 and 49 d compared with those fed 1,000 IU/kg. 2. There were no significant differences observed for feed conversion, mortality, tibia ash, or number of broken bones during automated processing of male broilers fed the vitamin D sources, vitamin D level, or phosphorus feeding program.

10 FRITTS AND WALDROUP: VITAMIN D SOURCES AND REDUCED PHOSPHORUS Feeding 25-OH-D3 significantly increased severity of TD compared with chicks fed VIT-D3, but this measurement was subject to extreme variability. 4. The modified phosphorus program suggested in this report had no adverse effects on any performance factor and should aid in reduction of phosphorus excretion as well as reducing cost of production. REFERENCES AND NOTES 1. O Dell, B. L., A. R. de Boland, and S. R. Koirthohann Distribution of phytate and nutritionally important elements among the morphological components of cereal grains. J. Agric. Food Chem. 20: Raboy, V Biochemistry and genetics of phytic acid synthesis. Pages in Inositol Metabolism in Plants. D. J. Moore, W. Boas, and F. A. Lowus, ed. Wiley-Liss, New York. 3. Nelson, T. S., J. J. McGillivray, T. R. Shieh, R. J. Wodzinski, and J. H. Ware Effects of phytate on the calcium requirement of chicks. Poult. Sci. 47: Nelson, T. S., T. R. Shieh, R. J. 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Approximately 10 s after stunning, a deep manual throat cut was made to sever the carotid artery and jugular vein with a 120-s bleed time. Carcasses were scalded at 128 F in an inline scalder, defeathered in an inline picker for 70 s, and rinsed for 10 s in an inside-outside online rinse cabinet. The carcasses were removed from the slaughter line by passing through an automatic hock cutter, and necks severed by pneumatic cutters. The carcasses were then rehung on the evisceration line and proceeded through an automated vent cutter and opening machine and viscera drawn from the carcass by automated evisceration. The viscera were then manually removed from the carcass. 53. SAS Institute SAS User s Guide: Statistics. Version 6.03 ed. SAS Institute Inc., Cary, NC. 54. Rennie, J. S., and C. C. Whitehead Effectiveness of dietary 25- and 1-hydroxycholecalciferol in combating tibial dyschondroplasia in broiler chickens. Br. Poult. Sci. 37: Roberson, K. D Hydroxycholecalciferol fails to prevent tibial dyschondroplasia in broiler chicks raised in battery brooders. J. Appl. Poult. Res. 8: Bar, A., V. Razaphkovsky, E. Vax, and I. Plavnik Performance and bone development in broiler chickens given 25- hydroxycholecalciferol. Br. Poult. Sci. 44: Ledwaba, M. F., and K. D. Roberson Effectiveness of 25-hydroxycholecaliferol in the prevention of tibial dyschondroplasia in Ross cockerels depends on dietary calcium level. Poult. Sci. 82: Zhang, X., G. Liu, G. R. McDaniel, and D. A. Roland Responses of broiler lines selected for tibial dyschondroplasia incidence to supplementary 25-hydroxycholecalciferol. J. Appl. Poult. Res. 6: Zu, T.-S., R. M. Leach, Jr., B. Hollis, and J. H. Soares, Jr Evidence of increased cholecalciferol requirement in chicks with tibial dyschondroplasia. Poult. Sci. 76: Acknowledgments The authors express their thanks to BASF Corporation for donation of phytase and phytase assays, to Alpharma for donation of cholecalciferol, to Monsanto Animal Nutrition for donation of 25- hydroxy-cholecalciferol and vitamin assays, to Roche Vitamins for assay of cholecalciferol, to Cobb-Vantress for donation of chicks, and to Mineral Associates, Inc., for donation of trace mineral mix.