Hy-Line W-36 and Hy-Line W-98 Laying Hens Respond Similarly to Dietary Phosphorus Levels

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1 Hy-Line W-36 and Hy-Line W-98 Laying Hens Respond Similarly to Dietary Phosphorus Levels J. L. Snow, K. A. Rafacz, P. L. Utterback, C. W. Utterback, R. W. Leeper, and C. M. Parsons 1 University of Illinois Department of Animal Sciences, 284 Animal Sciences Laboratory, 1207 West Gregory Drive, Urbana, Illinois ABSTRACT Two experiments were conducted to determine strain, there was no significant difference in egg production if 2 laying hen strains, Hy-Line W-36 and Hy-Line W-98, would respond similarly to being fed corn-soybean performance for hens fed 0.14% NPP compared with hens fed 0.45% NPP. In experiment 2, 3 diets with varying meal diets (17% CP and 3.8% Ca) deficient in nonphytate levels of NPP (0.10, 0.13, and 0.45%) were fed to 5 replicate P (NPP). In experiment 1, 3 diets with varying NPP levels groups of 12 hens of each Hy-Line strain from 95 to 112 wk of age. The 0.10% NPP treatment rapidly and severely (0.10, 0.14, and 0.45%) were fed to 6 replicate groups of depressed egg production and was terminated at 99 wk 12 hens of each Hy-Line strain from 20 to 50 wk of age. of age for both strains. In addition, egg production and Body weight, egg weight, egg mass, feed intake, and NPP egg mass were depressed similarly in both strains fed intake were higher for W-98 hens compared with W % NPP. In conclusion, this research indicates that Hyhens throughout the 30-wk period. The 0.10% NPP dietary Line W-36 and Hy-Line W-98 hens responded similarly treatment was terminated for both strains at 35 wk of age due to similar low egg production. Within each to dietary NPP deficiency, suggesting that both strains have similar NPP requirements. (Key words: deficiency, laying hen, nonphytate phosphorus, phosphorus, requirement) 2005 Poultry Science 84: INTRODUCTION Many factors have been reported to affect the P requirement of laying hens. Such factors include cage density (Sohail et al., 2001), dietary calcium levels (Hurwitz and Bar, 1965; Scheideler and Sell, 1986; Keshavarz, 1987; Hartel, 1989), environmental temperatures (Chandramoni et al., 1998), and housing systems (Singsen et al., 1962). The effects of laying hen strain on the nonphytate P (NPP) requirement have not been evaluated extensively. Layer management guides from breeder companies often recommend levels from 0.3 to 0.5% NPP, and the recommendations often differ for different strains of White Leghorn hens. Two of the most common layer strains in the US, Hy-Line W-36 and Hy-Line W- 98, are good examples of strain differences in dietary NPP recommendations. The Hy-Line management guides (Hy-Line International, 2003, 2004) suggest that W-36 layers be fed 0.45, 0.42, 0.37, and 0.34% NPP from 50% egg production to 32 wk of age, 32 to 44 wk of age, 44 to 58 wk of age, and greater than 58 wk of age, respectively, during the first production cycle, and 0.42, 2005 Poultry Science Association, Inc. Received for publication June 25, Accepted for publication November 28, To whom correspondence should be addressed: poultry@uiuc.edu. 0.38, 0.35, and 0.33% NPP for increasing age periods during the second production cycle. In contrast, it is recommended that W-98 hens are fed higher levels (0.50, 0.45, 0.40, and 0.35% NPP) for the first and second production cycles at the same age periods and production levels as those for the W-36 strain. It was our objective to determine how W-36 and W- 98 Hy-Line strains would respond to being fed diets deficient and adequate in NPP. If the W-98 strain does, indeed, require higher levels of NPP than the W-36 strain, we would expect that egg production of the W- 98 strain would be reduced to a greater extent by feeding NPP-deficient diets. It was our hypothesis that both strains would respond similarly to NPP-deficient diets during both the first and second production cycles, indicating similar NPP requirements. It was also of interest to assess the effects of dietary NPP levels on incidence of visceral gout, bone integrity, and kidney histology via postmortem evaluation. Experiment 1 MATERIALS AND METHODS The University of Illinois Institutional Animal Care and Use Committee approved all animal procedures. Abbreviation Key: NPP = nonphytate phosphorus. 757

2 758 SNOW ET AL. TABLE 1. Composition of the basal diet Ingredients % Yellow-dent corn Soybean meal, dehulled (48% CP) Limestone 9.80 Salt 0.40 Vitamin mix Mineral mix DL-Methionine 0.10 Choline chloride (60%) 0.05 Larvadex Composition, calculated Protein (%) TME (kcal/g) 2.86 Calcium (%) 3.80 Nonphytate P (%) 0.10 Lys (%) 0.88 Met + Cys (%) 0.67 Analyzed total P 4 (%) Provided per kilogram of diet: retinyl A acetate, 4,400 IU; cholecalciferol, 25 µg; DL-α-tocopheryl acetate, 11 IU; vitamin B 12, 0.01 mg; riboflavin 4.41 mg; D-pantothenic acid, 10 mg; niacin, 22 mg; menadione sodium bisulfite, 2.33 mg. 2 Provided as milligrams per kilogram of diet: manganese, 75 from manganese oxide; iron, 75 from iron sulfate; zinc, 75 from zinc oxide; copper, 5 from copper sulfate; iodine, 0.35 from ethylene diamine dihydroiodide; selenium, 0.2 from sodium selenite. 3 Novartis Animal Health, Greensboro, NC. 4 Determined from a composite of all basal diet samples taken from the various feed mixings during the experiment. Two hundred sixteen Hy-Line W-36 and 216 Hy-Line W-98 2 hens were randomly assigned to 1 of 3 dietary treatments from 20 to 50 wk of age. Beginning at 18 wk of age, the hens were fed a diet (17% CP, 3.8% Ca, and 0.45% NPP) that met or exceeded all nutrient requirements (NRC, 1994), and they were reared in the same growing environment from hatching. The hens used in this experiment were housed in a completely enclosed, ventilated, conventional caged-layer building in which the daily photoperiod was 16L:8D. The experiment was started in September and was completed in April. Treatments were arranged in a factorial design with 3 NPP levels and 2 strains. Hens were allotted to treatments so that the mean BW for each treatment was similar. Each experimental diet was fed to 6 replicate groups of 12 hens. A replicate group consisted of 4 adjacent cages of 3 hens per cage and each cage measured cm. Feed and water were provided for ad libitum consumption. The composition of the basal corn-soybean meal diet with no supplemental P is provided in Table 1 and was calculated to contain 17% CP, 3.8% Ca, and 0.1% NPP. Calculations of dietary NPP content were made using NRC (1994) NPP concentrations for corn and soybean meal. The 3 experimental diets were formulated to contain 0.10, 0.14, and 0.45% NPP by adding the dicalcium phosphate in place of corn and limestone to maintain 2 Hy-Line International, Des Moines, IA. 3 University of Missouri-Columbia, MO. Ca at 3.8%. The 0.10% NPP level was selected to provide a definite P-deficient diet, and the 0.14% NPP level was chosen to be marginally deficient based on previous studies from our laboratory (Boling et al., 2000a,b; Snow et al., 2003, 2004). The 0.45% NPP diet was included as a positive (nondeficient) control diet. Samples of the 0.10% NPP diet were taken each time diets were mixed (approximately every 4 wk). The diet samples were then driedfor24hat100 C, weighed, and dry-ashed for 24 h in a muffled furnace at 600 C. Total P analysis of the diet samples was performed via wet-ash using HNO 3 and H 2 O 2 (Wedekind et al., 1991, 1992) and then colorimetrically analyzed for P content according to Association of Official Analytical Chemists (1980). The basal diet was analyzed to contain 0.29% total P. Egg production and mortality were recorded daily. Egg weights (g/egg), egg mass (g of egg produced/day, egg production egg weight), and feed consumption were measured biweekly. Body weights were obtained every 4 wk. After euthanasia of hens with CO 2 gas, samples of uterus, peripheral nerve, muscle, spleen, proventriculus, pancreas, duodenum, kidney, heart, liver, ribs, and tibia were randomly obtained from 1 or 2 hens from each treatment at 30, 36, 38, and 42 wk of age and from 6 hens per treatment at 50 wk of age (1 per replicate group). The hens were visually examined for signs of gout, skeletal integrity, and beading of the rib bones at these same times. Tissue samples were sent to the University of Missouri Veterinary Diagnostic Laboratory 3 for histological examination. In addition, the tibiae obtained at 50 wk of age were autoclaved and the adhering tissue was removed. The cleaned tibiae were dried, dry-ashed, and analyzed for total P content as described earlier. Experiment 2 This experiment was conducted to determine if the results obtained in experiment 1 would be similar to those obtained in second-cycle (molted) hens. One hundred eighty Hy-Line W-36 and W-98 hens were randomly assigned to 1 of 3 diets containing varying NPP levels (0.10, 0.13, 0.45%) from 95 to 112 wk of age. These hens were selected from a large group of hens that had not been used in experiment 1, but were obtained from the same hatch as those in experiment 1 and reared together thereafter. The hens had been molted at 65 wk of age and had been fed a diet containing 17% CP, 3.8% Ca, and 0.45% NPP that met or exceeded all nutrient requirements (NRC, 1994) before the start of this experiment. Hens were allotted to treatments so that mean BW was similar (difference among treatments was 1% or less). Each experimental diet was fed to 5 replicate groups of 12 hens, with a replicate group consisting of 4 adjacent cages of 3 hens per cage and each cage measured cm, as in experiment 1. Hens were provided ad libitum access to feed and water. The composition of the 0.10% NPP basal diet was the same

3 AVAILABLE PHOSPHORUS REQUIREMENT OF HY-LINE STRAINS 759 FIGURE 1. Biweekly hen-day egg production from W-36 and W-98 hens fed different nonphytate phosphorus (NPP) levels from 20 to 50 wk of age in a factorial design investigating 2 strains and 3 dietary NPP levels. There were no significant interactions between dietary NPP and strain on egg production at any time during this study. There was a significant strain effect from 21 to 24 wk of age. Both strains of hens on the 0.10% NPP treatment showed significant reductions in egg production from 27 to 35 wk of age, when this treatment was terminated due to low egg production. There were no significant effects of strain or dietary NPP level on egg production from 36 to 50 wk of age. as that in experiment 1 (Table 1). Egg production and mortality were again recorded daily, and egg weights, egg mass, and feed consumption were measured biweekly. At 99 wk of age, 5 hens per treatment (1 per replicate group) were randomly selected, euthanized with CO 2 gas, and then visually examined for production status, signs of gout, skeletal integrity, and beading of the rib bones. At the same time, tibiae were obtained for bone ash determination. The tibiae and a composite sample of the 0.10% NPP diet were analyzed for total P using the same procedure as in experiment 1. Statistical Analysis Data from both experiments were analyzed by AN- OVA using the GLM procedures of SAS for a factorial arrangement (3 NPP levels 2 strains) to determine interactions and main effects at various time points (SAS Institute, 1990). Differences among individual treatments were determined using the least significant difference test (Carmer and Walker, 1985). Experiment 1 RESULTS Biweekly hen-day egg production is shown in Figure 1. There were no significant dietary NPP strain interactions for egg production during the 30-wk trial. The W- 36 hens came into production slower than the W-98 hens, resulting in a significant strain main effect from 21 to 24 wk of age. There were no significant strain effects for egg production from 25 to 50 wk of age. Beginning at 27 wk of age, both strains fed the 0.10% NPP diet showed depressions (P < 0.05) in egg production, resulting in a dietary NPP level effect (P < 0.05) from 27 to 35 wk of age. The 0.10% NPP treatment was terminated at 35 wk of age due to low egg production. There were no significant dietary NPP level or strain main effects on egg production from 36 to 50 wk of age. Production performance and tibia ash are summarized for 20 to 50 wk of age in Table 2. Because the 0.10% NPP treatment was terminated early, only the 0.14 and 0.45% NPP treatments are presented in Table 2. Calculated NPP intakes for the W-36 hens fed 0.14 and 0.45% NPP were 141 and 467 mg/hen per d and intakes for W-98 hens fed the 0.14 and 0.45% NPP were 153 and 516 mg/hen per d, respectively. A significant interaction between dietary NPP and strain was observed for the NPP intake. The interaction resulted because the difference in NPP intake between the dietary NPP levels or concentrations was greater for the W-98 hens than the W-36 hens. There were no significant interactions for any of the other production parameters. The W-98 hens had significantly higher hen-day egg production, BW, egg weight, and egg mass than W-36 hens, resulting in (P < 0.05) strain effects for these parameters. Dietary NPP level, however, did not significantly affect henday egg production, BW, egg weight, egg mass, or feed efficiency. Both strain and dietary NPP significantly affected feed intake such that the W-36 hens consumed less than the W-98 hens and hens fed 0.14% NPP diet had lower feed intakes than hens fed 0.45% NPP. Dietary NPP did not affect tibia ash; however, there was a signif-

4 760 SNOW ET AL. TABLE 2. Performance of 2 strains of hens (Hy-Line W-36 and Hy-Line W-98) fed different dietary nonphytate phosphorus (NPP) levels from 20 to 50 wk of age, experiment 1 Dietary NPP level, 1 % W-36 W-98 Main effects (P) Pooled Response SEM Strain Dietary NPP Performance 2 NPP intake, 3 mg/hen per d 141 d 467 b 153 c 516 a 3.2 <0.001 <0.001 BW, g/hen 1,481 b 1,519 b 1,677 a 1,694 a 20.6 <0.001 NS Egg production, % 88 b 88 b 92 a 92 a 0.7 <0.001 NS Egg weight, g/egg 55 b 55 b 58 a 58 a 0.4 <0.001 NS Egg mass, g/hen per d 50 b 50 b 54 a 55 a 0.6 <0.001 NS Feed intake, g/hen per d 101 c 104 c 109 b 115 a 1.2 < Feed efficiency, g/g NS Tibia ash 4 at 50 wk of age, % 62 a 62 a 59 b 60 ab NS a d Means within a row with no common superscript are significantly different (P < 0.05). 1 A 0.10% NPP treatment was also included in this experiment. That treatment was terminated at 35 wk of age due to low egg production. 2 Values are means for 6 replicate groups of 12 hens per treatment. 3 A significant NPP level strain interaction occurred (P = 0.001). 4 Values are means of 6 tibiae per treatment (1 tibia per replicate group). icant strain effect, with the W-36 hens having higher tibia ash than the W-98 hens. No visual signs of gout were found in any of the hens examined. There was beading of the rib bones and some signs of ovarian regression in the hens fed the 0.10% NPP diet at 36 wk of age. By 50 wk of age, the hens fed 0.14% NPP had thinner visceral fat pads, but skeletal integrity was similar to hens fed the 0.45% NPP. Tissue histology results indicated that the hens fed the 0.10% NPP diet had minor kidney abnormalities compared with the hens fed the 0.45% NPP diet. However, all other tissues from the hens fed the 0.10% NPP diet were normal. Histological analyses of the tissues for the hens fed 0.14 and 0.45% NPP were normal at all examination times. Experiment 2 At 97 wk of age, hen-day egg production began to decrease (P < 0.05) for both the W-36 and W-98 hens fed the 0.10% NPP diet (Figure 2). The 0.10% NPP diet was terminated at 99 wk of age due to low egg production. When averaged for the entire 99 to 112 wk period, both strains of hens fed the 0.13% NPP diet had lower (P < 0.05) egg production than hens fed the 0.45% NPP diet. Throughout the 17 wk trial, both the W-36 and W- 98 hens fed the 0.45% NPP diet had similar egg production. Egg weight, egg mass, feed intake, and NPP intake were higher for the W-98 hens compared with W-36 hens for the 17-wk period (Table 3). There were significant dietary NPP and strain interactions for NPP intake, egg mass, and feed efficiency. The interaction for NPP intake occurred because the difference in NPP intake between strains was greater at 0.45% NPP than at 0.13% NPP. The interaction for egg mass resulted because egg mass for both strains was similar at 0.45% NPP, but egg mass was lower for W-36 than W-98 hens at 0.13% NPP. The interaction for feed efficiency resulted because the value was similar for both strains at 0.13% NPP but W-36 hens had higher feed efficiency than W-98 hens at 0.45% NPP. Dietary NPP level did not significantly affect tibia ash. At 99 wk of age, some kidney atrophy, liver abnormalities, beading of the rib bones, and signs of ovarian regression were observed in hens fed the 0.10% NPP diet, but none in hens fed the 0.13 and 0.45% NPP diets. There were no visual signs of gout in any of the hens examined. DISCUSSION Our data demonstrate that there is not a substantial difference in the NPP requirement between W-36 and W-98 hens. The 2 strains of hens showed similar large decreases in egg production when fed a P-deficient (0.10% NPP) diet in both experiments. Sohail and Roland (2002) also observed a rapid decrease in egg production when young and old hens were fed 0.10% NPP. Our results are in agreement with those of Said et al. (1984), who reported that the NPP requirement of 2 strains of White Leghorn laying hens did not differ in the first egg production cycle. When hens were fed a marginally deficient NPP diet (0.13%) during the second cycle of experiment 2 in our study, egg production was significantly lower for the W-36 hens compared with W-98 hens. At first glance, these results suggested that second-cycle Hy-Line W-36 hens might be more sensitive to NPP deficiencies than second-cycle W-98 hens. Upon further examination, however, it is apparent that the lower egg production of the W-36 hens was primarily due to lower egg production at the beginning of experiment 2 (Figure 2). Thus, the change in egg production during the experiment (initial vs. final) was not significantly different for the 2 strains of hens (i.e., egg

5 AVAILABLE PHOSPHORUS REQUIREMENT OF HY-LINE STRAINS 761 FIGURE 2. Biweekly hen-day egg production from W-36 and W-98 hens fed different nonphytate phosphorus (NPP) levels from 95 to 112 wk of age in a factorial design investigating 2 strains and 3 dietary NPP levels. There were no significant interactions between dietary NPP and strain on egg production at any time during this study. There was a significant diet effect from 97 to 112 wk of age. Both strains of hens on the 0.10% NPP treatment showed significant reductions in egg production from 97 to 99 wk of age, when this treatment was terminated due to low egg production. Both strains of hens fed the 0.13% NPP treatment showed significant reductions in egg production from 101 to 112 wk of age. production decreased from 81% at 95 wk of age to 42% at 99 wk of age for the W-98 hens compared with a decrease from 75% at 95 wk of age to 33% at 99 wk of age for the W-36 hens). Our results suggest that the NPP requirement of W-36 and W-98 hens is similar and that W-98 hens do not need to be fed higher levels of NPP. Results for the hens fed the 0.14% NPP diet in experiment 1 were surprising because we expected this NPP level to be marginally deficient. However, our egg production performance and tibia ash results indicated that this diet was adequate in NPP for the hens from 20 to 50 wk of age. The analyzed total P content of our basal diet was 0.29%, which is similar to the calculated level of 0.33%. The lower feed intake of hens fed 0.14% NPP compared with 0.45% NPP suggested that the 0.14% NPP diet may have been very slightly deficient in NPP. Although a precise NPP requirement cannot be ascertained from our study, our results indicated that the dietary NPP requirement did not greatly exceed 0.14% for experiment 1. Several other studies have reported low NPP levels to provide maximal production performance. Van der Klis et al. (1997) reported that the NPP requirement was only 0.13 to 0.16% NPP for laying hens from 20 to 68 wk of age. Boling et al. (2000a,b) found that 0.15% NPP supported optimal layer performance from 20 to 60 or 70 wk of age. In addition, the NPP requirement for firstcycle laying hens was reported to be only 0.16% NPP by Boorman and Gunaratne (2001). Therefore, there is considerable evidence that the minimal NPP require- TABLE 3. Performance of 2 strains of hens (Hy-Line W-36 and Hy-Line W-98) fed different dietary nonphytate phosphorus (NPP) levels from 95 to 112 wk of age, experiment 2 Dietary NPP levels, 1 % W-36 W-98 Main effects Pooled Response SEM Strain Dietary NPP Performance 2 NPP intake, 3 mg/hen per d 132 d 460 b 149 c 524 a 5.5 <0.001 <0.001 Egg production, % 60 c 73 a 67 b 73 a 1.8 NS < Egg weight, g/egg 64 c 66 b 67 a 68 a 0.5 < Egg mass, 3 g/hen per d 39 c 49 ab 46 b 50 a <0.001 Feed intake, g/hen per d 101 b 103 b 114 a 117 a 1.6 < NS Feed efficiency, 3 g/g 0.39 c 0.48 a 0.40 c 0.43 b 0.01 <0.048 <0.001 Tibia ash 4 at 99 wk of age, % 50 a 51 a 50 a 51 a 0.6 NS NS a d Means within a row with no common superscript are significantly different (P < 0.05). 1 A 0.10% NPP treatment was also included in this experiment. That treatment was terminated at 99 wk of age due to low egg production. 2 Values are means for 5 replicate groups of 12 hens per treatment. 3 A significant NPP level strain interaction occurred (P < 0.05). 4 Values are means of 5 tibiae per treatment (1 tibia per replicate group).

6 762 SNOW ET AL. ment of first-cycle laying hens is less than 0.20%, which is lower than that recommended by NRC (1994) and much lower than that generally recommended by layer management guides of breeder companies. Our results and those from several other studies indicate that laying hens can be fed NPP levels that are substantially lower than those generally recommended by breeder companies and those commonly fed by industry. The latter practice would reduce feed cost and environmental pollution due to high P excretion levels. Tissue histology did not indicate that the hens had any signs of visceral gout in the samples taken at various times throughout this study. Visceral gout is sometimes seen in commercial laying hens and it is often thought to be due to a dietary P deficiency (L. Eldridge and S. Frankenbach, Purina Mills/Land O Lakes, Kansas City, MO; personal communication). The latter has not been substantiated by research. Visceral gout is a disease in which urates form on the serosal membranes of several tissues including the joints, heart, liver, fat, spleen, kidney, lungs, and other tissues (Sonemez, 1991). Many factors have been reported to cause gout, including excess dietary sodium bicarbonate (Davison and Wideman, 1992), fowl influenza (Slemons et al., 1990), mycotoxins in corn (Schlosberg et al., 1997), nephritis induced by infectious bronchitis virus or the spray vaccination, Newcastle disease or the spray vaccination, adenovirus or reovirus infections, shipping stress, Mycoplasma synoviae infection, immune complex disease, and water deprivation (Mallinson et al., 1984). In our study, the hens fed the 0.10% NPP diet did show some minor kidney abnormalities but no signs of gout. No abnormalities in tissue histology were observed in hens fed NPP levels greater than 0.10%. Thus, results indicated that feeding P-deficient diets did not cause visceral gout in young (first-cycle) or older (secondcycle) hens of 2 different strains. Our results support the conclusion that Hy-Line W- 36 and W-98 strains of hens respond similarly when fed NPP-deficient diets, suggesting that they have similar NPP requirements. In addition, we observed no histological signs of visceral gout in hens fed low NPP diets. ACKNOWLEDGMENTS The authors would like to express their gratitude to Stephanie Frankenbach, Ray Zimmerman, and Leo Eldridge of Purina Mills/Land O Lakes (Kansas City, MO) for their financial and technical assistance, and Alex Bermudez of University of Missouri-Columbia (Columbia, MO) for his histological expertise. REFERENCES Association of Official Analytical Chemists Official Methods of Analysis. 13th ed. Association of Official Analytical Chemists, Washington, DC. Boling, S. D., M. W. Douglas, M. L. Johnson, X. Wang, C. M. Parsons, K. W. Koelkebeck, and R. A. Zimmerman. 2000a. The effects of dietary available phosphorus levels and phytase on performance of young and older laying hens. Poult. Sci. 79: Boling, S. D., M. W. Douglas, R. B. Shirley, C. M. Parsons, and K. W. Koelkebeck. 2000b. The effects of various dietary levels of phytase and available phosphorus on performance of laying hens. Poult. Sci. 79: Boorman, K. N., and S. P. Gunaratne Dietary phosphorus supply, egg-shell deposition and plasma inorganic phosphorus in laying hens. Br. Poult. Sci. 42: Carmer, S. G., and W. M. Walker, Pairwise multiple comparisons of treatment means in agronomic research. J. Agron. Educ. 14: Chandramoni, S., B. Jadhao, and R. P. Sinha Effects of dietary calcium and phosphorus concentrations on retention of these nutrients by caged layers. Br. Poult. Sci. 39: Davison, S., and R. F. Wideman Excess sodium bicarbonate in the diet and its effect on Leghorn chickens. Br. Poult. Sci. 33: Hartel, H Evaluation of the dietary interaction of calcium and phosphorus in the high producing laying hen. Br. Poult. Sci. 31: Hurwitz, S., and A. Bar Absorption of calcium and phosphorus along the gastrointestinal tract of the laying fowl as influenced by dietary calcium and egg shell formation. J. Nutr. 86: Hy-Line International Hy-Line Variety W-36 Commercial Management Guide. Hy-Line International, Des Moines, IA. Hy-Line International Hy-Line Variety W-98 Commercial Management Guide. Hy-Line International, Des Moines, IA. Keshavarz, K Interaction between calcium, and phosphorus in laying hens. Nutr. Rep. Int. 36:9 20. Mallinson, E. T., H. Rothenbacher, R. F. Wideman, D. B. Snyder, E. Russek, A. I. Zuckerman, and J. P. Davidson Epizootiology, pathology, and microbiology of an outbreak of urolithiasis in chickens. Avian Dis. 28: NRC Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC. Said, N. W., T. W. Sullivan, M. L. Sunde, and H. R. Bird Effect of dietary phosphorus level and source on productive performance and egg quality of 2 commercial strains of laying hens. Poult. Sci. 63: SAS Institute SAS/STAT User Guide: Statistics. Release 6.04 ed. SAS Institute Inc., Cary, NC. Scheideler, S.E. and J. L. Sell Effects of calcium and phase-feeding phosphorus on production traits and phosphorus retention in 2 strains of laying hens. Poult. Sci. 65: Schlosberg, A., N. Elkin, M. Malkinson, U. Orgad, V. Hanji, E. Bogin, Y. Weisman, M. Meroz, and R. Bock Severe hepatopathy in geese and broilers associated with ochratoxin in their feed. Mycopathologia 138: Singsen, E. P., A. H. Spandorf, L. D. Matterson, J. A. Serafin, and J. J. Tlustohowicz Phosphorus in the nutrition of the adult hen 1. Minimum phosphorus requirements. Poult. Sci. 41: Slemons, R. D., L. N. Locke, M. G. Seerar, R. M. Duncan, V. S. Hinshaw, B. C. Easterday Kidney lesions associated with mortality in chickens inoculated with waterfowl influenza viruses. Avian Dis. 34: Snow, J. L., M. W. Douglas, A. B. Batal, M. E. Persia, P. E. Biggs, and C. M. Parsons Minimal phosphorus requirement of one-cycle and two-cycle (molted) hens. Poult. Sci. 83: Snow, J. L., M. E. Persia, P. E. Biggs, D. H. Barker, and C. M. Parsons α-Hydroxycholecalciferol has little effect on phytate phosphorus utilization in laying hen diets. Poult. Sci. 82:

7 AVAILABLE PHOSPHORUS REQUIREMENT OF HY-LINE STRAINS 763 Sohail, S. S., M. M. Bryant, S. K. Rao, and D. A. Roland Influence of cage density and prior dietary phosphorus level on phosphorus requirement of commercial Leghorns. Poult. Sci. 80: Sohail, S. S., and D. A. Roland Influence of dietary phosphorus on performance of Hy-Line W36 hens. Poult. Sci. 81: Sonemez, G Organic distribution and interrelationships of lesions occurring in laying hens suffering from gout and urolithiasis. Adv. Exp. Med. Biol. 309A: Van der Klis, J. D., H. A. J. Versteegh, P. C. M. Simons, and A. K. Kies The efficacy of phytase in corn-soybean meal-based diets for laying hens. Poult. Sci. 76: Wedekind, K. J., A. E. Hortin, and D. H. Baker Methodology for assessing zinc bioavailability: Efficacy estimates for zinc-methionine, zinc sulfate and zinc oxide. J. Anim. Sci. 70: Wedekind, K. J., E. C. Titgemeyer, A. R. Twardock, and D. H. Baker Phosphorus, but not calcium, affects manganese absorption and turnover in chicks. J. Nutr.121: