EFFECTS OF SOURCE AND PARTICLE SIZE ON THE BIOLOGICAL AVAILABILITY OF CALCIUM IN CALCIUM SUPPLEMENTS FOR GROWING PIGS 1'2

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1 EFFECTS OF SOURCE AND PARTICLE SIZE ON THE BIOLOGICAL AVAILABILITY OF CALCIUM IN CALCIUM SUPPLEMENTS FOR GROWING PIGS 1'2 Summary Five experiments were cnducted t determine the bilgical availability f the Ca in high-ca (calcitic) limestne, dlmitic limestne, yster shell flur, gypsum, marble dust and aragnite fr the grwing pig, and t determine the influence f particle size f the Ca surce n the biavailability f Ca. A lw-ca, frtified, crn sybean meal basal diet calculated t cntain.2% Ca and.6% P was used. This diet was supplemented with 0 r.3% Ca frm either CaCO3 precipitate (the standard) r the test surce f Ca. Diets were fed n an ad libitum basis t three t eight replicate pens f pigs (ne r tw/pen) fr 35 t 42 d. Average initial weight f the pigs was 15 kg. At the end f each experiment the pigs were killed, the third and furth metacarpals and metatarsals and the femurs were remved, and breaking strength and ash were determined. The increase in bne strength frm feeding the test surce f Ca relative t the increase in bne strength frm feeding the CaCO3 standard was used t calculate the relative availability f Ca in the supplements. The biavailability f Ca in calcitic limestne (tw surces), yster shell flur, gypsum, marble dust and aragnite was similar, ranging frm 93 t 102%. Hwever, the Ca in tw surces f dlmitic limestne was less available (51 and 78%) than in the ther surces. Particle size f the Ca surces (gemetric mean diameter f.10 t.54 mm) did nt influence the availability f Ca. (Key Wrds: Pig, Calcium Surces, Calcium Availability, Particle Size, Bne Strength.) R. D. Rss 3, G. L. Crmwell and T. S. Stahly University f Kentucky, Lexingtn Jurnal Paper N f the Kentucky Agr. Exp. Sta., Dept. f Anita. Sci. ~Supprted in part by a grant-in-aid frm Iwa Limestne C., Des Mines, IA Current address: Marshall Minerals, Inc., 707 Evans St., Marshall, TX Received September 26, Accepted January 3, Intrductin Cereal grains and sybean meal are quite lw in Ca; therefre, diets utilizing these ingredients must be supplemented with substantial amunts f Ca (.35 t.70%) t meet the pig's requirement. High-Ca (calcitic) limestne is the supplement mst cmmnly used in the feed industry. Less cmmn surces f Ca include dlmitic limestne, yster shell flur, gypsum, marble dust and aragnite. Generally, it is assumed that the Ca in these surces is equally available, but this has nt been well dcumented with the pig. Studies with chicks have shwn that the availability f Ca in varius Ca surces varied frm 68 t 117% (Dilwrth et al., 1964; Waldrup et al., 1964; Reid and Weber, 1976). In pigs, early studies by Thmas et al. (1933) and McCampbell and Aubel (1934) and mre recent studies by Eggert et al. (1959) and Cmbs and Wallace (1962) shwed little difference in grwth rate r bne ash in pigs fed limestne, dicalcium phsphate r gypsum. The effects f particle size n the biavailability f Ca in Ca supplements als is nt'well dcumented. In ne study, particle size f limestne did nt affect perfrmance r bne traits in pigs (Pnd et al., 1981). Results with cattle have been incnsistent, in that sme studies have shwn marked differences in perfrmance when limestnes f differing particle size were fed, while ther studies have shwn little effect f particle size (Owens, 1983). The bjectives f this research were t determine the effects f surce and particle size f Ca supplements n the bilgical availability f Ca fr the grwing pig. Materials and Methds One hundred eighty-fur crssbred, Hampshire-Yrkshire pigs initially averaging 15 kg were used in five experiments. In each experi- 125 JOURNAL OF ANIMAL SCIENCE, Vl. 59, N. 1, 1984

2 126 ROSS ET AL. TABLE 1. COMPOSITION OF BASAL DIETS Experiment Ingredient 1 2 t 5 Crn, grund (IFN 4-O2-931) Sybean meal, dehuued (IFN 5-O4-612) Grund limestne (IFN ).37 Mnsdium phsphate Ptassium chlride a Trace mineral mix b Vitamin mixc Antibitic d I Calculated analysis Calcium Phsphrus aadded as a surce f CI. The mnsdium phsphate supplied.2% Na, which met the requirement f the pig. bcntributed the fllwing, mg/kg f diet: 100 Zn; 50 Fe; 27 Mn; 5.5 Cu;.75 1;.1 Se. CCntributed the fllwing per kg f diet: vitamin A, 4,400 IU; vitamin D3, 880 IU; vitamin E, 22.0 IU; ribflavin, 8.8 mg; pantthenic acid, 22.0 mg; niacin, 44.0 mg; vitamin BI~, 22.0 gg. dcntributed 55 mg f chlrtetracycline/kg f diet. ment, the pigs were alltted randmly t treatments frm utcme grups based n weight, sex and ancestry. They were hused individually in.6 x 1.2 m flat-deck pens r tw/ pen in.8 x 1.6 m flat-deck pens with expanded metal flrs in a temperature-cntrlled building (20 t 22 C). Pens were equipped with a self-feeder and a nipple waterer. The pigs were allwed t cnsume their diets ad libitum. Pig weights and feed cnsumptin were determined at weekly intervals. Experiments were 35 t 42 d in length. The basal diets (16.3% prtein,.82% lysine) cnsisted f crn and dehulled sybean meal and were frtified with sufficient levels f vitamins and minerals t meet r exceed NRC (1979) standards, except fr Ca (table 1). The calculated levels f Ca in the basal diets were.05% (Exp. 1) and.20% (Exp. 2 t 5). Calcium was added t the basal diet as technical-grade 4 Fischer Scientific C., Fair Lawn, NJ. s j. T. Baker Chemical C., Phillipsburg, NJ. Perkin-Elmer Mdel 560, Nrwalk, CT. 7 Instrn Crp., Mdel TM, Cantn, MA. CaCO3 precipitate 4 (CaCO3) r as the Ca supplement under investigatin. Mnsdium phsphate s (NaH2PO4) was the surce f supplemental P. Dietary P was maintained at a level f.6% in all diets. A descriptin f the Ca surces and their particle sizes is given in table 2. Particle size is expressed as the percentage f the surce passing thrugh a.297 and.149 mm sieve (50 and 100 mesh, respectively) and as the gemetric mean diameter (ASAE, 1974). The Ca in the different surces was assayed by atmic absrptin spectrscpy 6, using standard prcedures. Upn cmpletin f each experiment, the pigs were killed (electrically stunned, then exsanguinated). The third and furth metacarpals and metatarsals and the femurs were remved. Strength f the bnes was determined with an Instrn instrument 7 by the prcedure f Crmwell et al. (1972). The bnes were placed in a hrizntal psitin n tw supprts (3.2 cm apart fr the metatarsals and metacarpals; 9.6 cm apart fr the femurs) and pressure was applied at the center f the bne. The maximum amunt f frce applied t the bne befre breaking was cnsidered as break-

3 CALCIUM SOURCES FOR PIGS 127 TABLE 2. DESCRIPTION OF CALCIUM SOURCES Surce.149 mm sieve Exp. n. Ca, % ( 100 mesh) Percentage f samples passing thrugh.297 mm sieve (50 mesh) Gemetric mean diameter, mma Calcitic limestne A b 38.4 Fine Medium 2, 3, Carse 2 ~1 25 Calcitic limestne B c Dlmitic limestne A d Dlmitic limestne B e Oyster shell flur f Marble dustg Fine Medium Carse Gypsum h Aragnite i 38.8 Fine Medium aasae (1974). blwa Limestne C., Des Mines, IA. CFranklin Limestne, C., Crab Orchard, TN. dplumrn Superfine Agricultural Limestne, Peebles, OH. ew M B Crp., Pasadena, CA. foyster Shell Prducts, Mbile, AL. ggergia Marble C., Tare, GA. hunited States Gypsum, Shals, IN. imarcna Ocean Industries, Ltd., Perth Amby, NJ. ing strength. The metatarsals (Exp. 1 t 5) and femurs (Exp. 4, 5) then were cut in half, cleaned, dried and extracted three times (24 h each) wih diethyl ether. After drying, the bnes were ashed at 600 C fr 24 h. Ash was expressed as a percentage f the dry, fat-free bne. The biavailability f Ca in the varius Ca surces was determined by single pint regressin (slpe-rati) techniques. Bne-breaking strength was the criterin upn which biavailability f Ca was based. This variable was chsen based n results f previus studies invlving similar prcedures fr determining P biavailability, in which bne strength gave a mre linear fit than did bne ash, when regressed n level f dietary P (Miracle et al., 1977; Stber et al., 1979). The increase in bne strength resulting frm feeding the test material relative t the increase in bne strength resulting frm feeding the CaCO3 standard was used t assess the bilgical availability f Ca in the test material (figure 1). This prcedure des nt measure the true availability f Ca, because nly abut ne-half f the dietary Ca is absrbed by the pig (Hansard et al., 1961; Besancn and Gueguen, 1969). Hwever, the prcedure des allw ne t cmpare the relative availability f varius Ca surces with a reference surce f highly available Ca (CaCOa precipitate). Data were analyzed as a randmized blck design using variance and cvariance prcedures (Steel and Trrie, 1960). The general linear mdel f the Statistical Analysis System (SAS,

4 128 ROSS ET AL. g m m i CaC03 Standard Added Ca, %: 0.3 Ttal Ca, %:.2.5 Relative C'; Availability = ~2x hl 100 Figure 1. Single pint assay system used t estimate the relative bilgical availability f Ca in Ca supplements, with technical grade, CaCO 3 precipitate as the standard. 1979) was used. Regressin analysis was used in Exp. 1 t test fr linearity and nnlinearity. In Exp. 2 t 5, the treatment sum f squares were partitined int apprpriate rthgnal cntrasts. In all analyses, the pen was cnsidered the experimental unit. Exp. 1. In rder fr the biavailability methd t be valid, the level f dietary Ca must be belw the requirement, and the respnse t Ca must be linear. This experiment was cnducted t evaluate the assay system and test fr linearity. The basal diet was calculated t cntain.05% Ca. All f the Ca in the basal diet was supplied by crn and sybean meal. Calcium was added at fur levels (.15,.30,.45,.60%), which prvided a range f.05 t.65% ttal dietary Ca. The added Ca was prvided by technical grade CaCO3 precipitate (40% Ca). Each diet was fed fr 42 d t six pigs (three replicate pens f tw pigs/pen), initially averaging 13.6 kg. Exp. 2. This experiment was cnducted t determine the effects f particle size f limestne n the biavailability f Ca. Sixty pigs initially averaging 14 kg were fed a lw Ca (.2%) basal diet r the basal with.3% added Ca frm the CaCO3 standard r frm a single calcitic limestne f three particle sizes (table 2). The fine, medium and carse limestnes differed in rate f reactivity (1.0, 18.8 and 68.5 rain, respectively). Rate f reactivity is a measure f the time fr a given amunt f limestne t neutralize a given amunt f acid (Nller et al., 1980), and is a functin f slubility and particle size (surface area) f the material. Each f the five diets was fed t six replicate pens f tw pigs each fr 42 d. Exp. 3. Pigs initially averaging 13.5 kg were fed the basal diet (.2% Ca) r the basal with.3% added Ca frm the standard (CaCO3), r the calcitic r dlmitic limestne (table 2). The dlmitic limestne cntained 11% Mg. Each diet was fed t three replicates f tw pigs fr 42 d. Exp. 4. Sixty-fur pigs averaging 15,1 kg initially were fed the basal diet (.2% Ca) r the basal with.3% Ca as CaCO3 (the standard), calcitic limestne, yster shell flur, gypsum (Ca sulfate), marble dust, r dlmitic limestne. The calcitic limestne was the same as the medium-sized limestne used in Exp. 2. The dlmite was frm a different surce than that used in Exp. 3, and analyzed 12% Mg. Tw marble dusts frm a single surce, but differing in particle size, were evaluated. They are classified as fine and medium (table 2). Each f the eight diets were fed t eight, individuallypenned pigs fr 35 d. Exp. 5. Thirty-six pigs initially averaging 16.6 kg were fed the basal diet (.2% Ca) r the basal supplemented with.3% Ca frm CaCO3, a secnd calcitic limestne (surce B), marble dust r aragnite. The tw particle sizes f aragnite (fine and medium) were btained by sifting a single surce thrugh a.297 mm (50 mesh) sieve (table 2). The marble dust was frm the same surce, but f a larger particle size (designated as carse) than that used in Exp. 4. Each f the six diets was fed t six individually penned pigs fr 35 d. R esu Its Exp. 1. Fur f the six pigs fed the.05% Ca level died befre the experiment was cmpleted. Death apparently was due t the extremely lw level f dietary Ca, because necrpsy reprts indicated multiple fractures and hemrrhaging. Grwth rate, feed intake and efficiency f feed utilizatin were markedly depressed in this treatment grup (table 3). A quadratic imprvement (P.01) in gain and feed/gain was bserved as the level f dietary Ca was increased. Feed intake increased linearly (P.01) with increasing Ca level.

5 CALCIUM SOURCES FOR PIGS 129 TABLE 3. EFFECTS OF LEVEL OF CALCIUM ON GROWTH RATE, FEED INTAKE, FEED:GAIN RATIO AND BONE STRENGTH AND ASH CONTENT OF GROWING PIGS (EXP. 1) a Item Added Ca, %:b Ttal Ca, %: CV c Daily gain, gd Daily feed, kg e Feed/gain d Metacarpal-metatarsal strength, kg ef Femur strength, k~ ef Metatarsal ash, %u~ aeach diet fed t three replicatins f tw pigs/pen, 13.6 t 35.0 kg. Fur f the six pigs n the lw Ca diet died befre the end f the experiment. bsurce f Ca was technical grade CaCO 3 precipitate. Ccefficient f variatin (100 s/z). dquadratic effect (P.O1). elinear effect (P.01). fr 2 fr metatarsal-metacarpal strength, femur strength and metatarsal ash was.973,.944 and.938, respectively. Avg Metacarpal-metatarsal strength and femur strength increased linearly (P.01) and metatarsal ash increased quadratically (P.05) with increasing level f Ca. Althugh the respnse in bne strength t Ca level was linear, there was evidence that the metacarpal-metatarsal strength was beginning t plateau between the.50 and.65% level f Ca. Because the biavailability assay necessitates that a range f Ca levels be used in which the respnse is linear, the highest level f Ca (.65%) was deleted in the subsequent studies. Als, the lwest level f Ca (.05%) caused a severe Ca deficiency, resulting in a high mrtality rate, s in subsequent experiments the.2% level f Ca was used as the basal diet. Exp. 2. Gain and feed intake increased (P.01) as a result f adding Ca t the basal diet (table 4). Althugh pigs fed the medium and carse limestne tended t cnsume mre feed and gain faster than thse fed the ther surces f Ca, the differences were nt significant (P>.05). Bne strength and ash increased (P.01) when Ca was added t the basal diet. Each f the three particle-sized limestnes resulted in similar bne strength and ash values as thse in pigs fed the CaCO3 standard, which indicates that the relative availability f the Ca was nt influenced by particle size. The availability f Ca in the fine, medium and carse limestnes based n an average f the metatarsal-metacarpal and femur strength was 96, 102 and 102%, respectively, relative t the CaCO3 standard. Exp. 3. An imprvement in gain and feed cnsumptin ccurred when Ca was added t the basal diet (table 5). Pigs fed the calcitic limestne tended t gain faster than thse fed dlmitic limestne, but this difference was nt significant (P>.05). Bne strength and ash increased (P.01) with added Ca. The pigs receiving the dlmitic limestne had lwer bne strength (P.01) and ash (P.05)values when cmpared with the pigs receiving the calcitic limestne, indicating that the Ca in dlmitic limestne is less available than the Ca in calcitic limestne. The relative availability f Ca in the calcitic and dlmite limestnes was 100 and 78%, respectively. Exp. 4. Daily gain and feed required/unit f gain were nt affected by the surce r level f Ca (table 6). Pigs receiving the CaCO3 standard cnsumed mre feed (P.05) than thse fed the ther surces f added Ca. Metacarpalmetatarsal strength, femur strength, metatarsal ash and femur ash were increased (P.01) when Ca was added t the basal diet. The bne data were similar fr the calcitic limestne, gypsum, yster shell flur and marble dust, indicating a similar availability f Ca. Bne strength f pigs

6 130 ROSS ET AL. TABLE 4. EFFECTS OF PARTICLE SIZE OF CALCITIC LIMESTONE ON PERFORMANCE, BONE STRENGTH AND ASH, AND BIOLOGICAL AVAILABILITY OF CALCIUM (EXP. 2) a Item Limestne A Surce f Ca: Basal CaCO 3 b Fine Medium Carse Added Ca, %: Ttal Ca, %: CV c Daily gain, gd Daily feed, kg d Feed/gain Metacarpal-metatarsal strength, kg d Femur strength, kjg d Metatarsal ash, %u Relative biavailability f Ca e Avg aeach diet fed t six replicatins f tw pigs/pen, 13.6 t 37.6 kg. btechnical grade CaCO 3 precipitate, the standard t which ther surces were cmpared. CCefficient f variatin (100 s/x). dbasal vs added Ca (P.01). ebased n an average f metatarsal-metacarpai and femur strength. TABLE 5. EFFECTS OF SOURCE OF LIMESTONE ON PERFORMANCE, BONE STRENGTH AND ASH, AND BIOLOGICAL AVAILABILITY OF CALCIUM (EXP. 3) a Item Limestne Surce f Ca: Basal CaCOab Calcitic (A) Dlmitic (B) Added Ca, %:.O.3,3.3 Ttal Ca, %:.2.5,5.5 CV c Daily gain, gd, Daily feed, kg a F eed/gain Metacarpal-metatarsal strength, kg d Femur strength, kjg d Metatarsal ash, %e Relative biavailability f Ca f Avg aeach diet fed t three replicatins f tw pigs/pen, 13.5 t 36.3 kg. btechnical grade CaCO 3 precipitate, the standard t which ther surces were cmpared. CCefficient f variatin (100 s/~-). dbasal vs added Ca (P.01). edlmite vs calcitic limestne (P.01). fbased n an average f metatarsal-metacarpal and femur strength.

7 CALCIUM SOURCES FOR PIGS 131 r~ v,-i 0 "6 t~ >,,.a..d ~>,.a e~ z :=- {/1 ~m.~ , z t~ [..., 9 ~ z r..) Z e~ tl.,.,..4,~..,:i I:I ~z ~ I::I ill,,-4 0 r~ i U M,q [-., r~,.,., t4 ~.~ = M [-

8 132 ROSS ET AL. fed dlmitic limestne was less (P.001)than fr thse fed the ther supplements. Similar trends ccurred in bne ash (P.05), indicating a lwer availability f Ca in dlmitic limestne than in the ther Ca surces. The relative availability f Ca was similar fr the calcitic limestne (95%), yster shell flur (98%), gypsum (99%) and the fine (100%) and medium (95%) marble dust, but was abut ne-half as much (51%) in the dlmitic limestne. Exp. 5. Daily gain, daily feed and feed/gain were nt influenced by surce r level f Ca (table 7). An imprvement (P.001) in bne strength and bne ash was bserved when Ca was added t the basal diet. N differences in bne measurements were fund amng any f the surces f Ca. The fine particle-sized aragnite resulted in slightly lwer bne strength when cmpared with the medium particle-sized aragnite, but the difference was nt significant. The relative availability f Ca was similar in the calcitic limestne, carse marble dust, fine aragnite and medium aragnite (99, 98, 93, and 102%, respectively). Discussin The methds used in this research t evaluate the biavailability f Ca in Ca supplements were adapted frm techniques used t estimate the availability f P in P supplements fr chicks (Nelsn and Walker, 1964) and in cnventinal feedstuffs fr chicks (Hayes et al., 1979) and pigs (Miracle et al., 1977; Stber et al., 1979). In the first experiment, the increase in bne strength with increasing dietary Ca level fit the linear regressin quite well (R 2 =.973 and.944 fr the metatarsal-metacarpal and femur, respectively). Deletin f the lwest and highest level f Ca imprved the fit (R 2 =.999 and.999, respectively). Bne strength was quite respnsive t dietary Ca level as evidenced by a 52% increase in metatarsal-metacarpal strength and a 59% increase in femur strength when.3% Ca was added t the basal diet. Crrespnding increases in ash were 7 and 3%, respectively. The respnsiveness f bne strength t added Ca and the linearity f the fit makes this a sensitive and valid methd fr estimating the biavailability f Ca in supplements fr pigs. TABLE 7. EFFECTS OF CALCIUM SOURCE ON PERFORMANCE, BONE STRENGTH AND ASH, AND BIOLOGICAL AVAILABILITY OF CALCIUM (EXP. 5) a Item Marble Aragnite Aragnite Surce f Ca: Basal CaCO 3b Limestne B (carse) (fine) (medium) Added Ca, %: Ttal Ca, %: CV c Daily gain, g Daily feed, kg Feed/gain Metacarpal-metatarsal strength, kg d Femur strength, kjg d Metatarsal ash, %ta Femur ash, %d Relative biavailability f Ca e Avg aeach diet fed t eight replicatins f ne pig/pen, 16.6 t 38.1 kg. btechnical grade CaCO 3 precipitate, the standard t which ther surces were cmpared. Ccefficient f variatin (100 s/z). dbasai vs ther surces f Ca (P.O01). ebased n an average f metatarsal-metacarpal and femur strength.

9 CALCIUM SOURCES FOR PIGS 133 An imprtant pint is that ur methd estimates the relative (nt true) availability f Ca, using a highly available surce f Ca (CaCO3 precipitate) as a reference standard. At best, nly abut 50% f the Ca frm a highly sluble surce f Ca (such as CaCO3) is absrbed frm the gut (Hansard et al., 1961; Besancn and Gueguen, 1969). With ur prcedure, variatin in feed intake (hence, Ca intake) may influence the accuracy f the estimates f Ca availability. Frtunately, feed intake did nt vary greatly amng the treatment grups in mst f the experiments. Tw alternate methds were used t crrect fr differences in feed intake. In ne methd, bne strength was regressed n Ca intake. In the secnd methd, bne strength was analyzed by cvariance, with feed intake as the cvariate. Breaking strength f the bnes was adjusted fr differences in feed intake and slpe ratis were then determined n the adjusted means. Neither methd changed the interpretatin f the data. Methd 1 resulted in a greater range f estimates f Ca availability (91 t 115 %) than the riginal methd (93 t 102%). Methd 2 resulted in a similar range f estimates (96 t 106%), with the means being slightly higher than fr the unadjusted means. Surce f Ca. The results f these experiments suggest that, fr the grwing pig, the Ca in calcitic limestne, yster shell flur, gypsum, marble dust and aragnite is highly available, ranging frm 93 t 102%. Hwever, the Ca in dlmitic limestne was nt as available (78% in Exp. 3, 51% in Exp. 4) as the Ca in the ther surces. The lwer availability f the Ca in dlmitic limestne may be due t its dense CaCO3 and MgCO3 structure. A pure calcitic limestne is cmpsed f calcite, which cnsists f crystals with alternating layers f Ca ins and carbnate ins (Byntn, 1980). In dlmitic limestne, Mg is substituted fr sme f the Ca in the crystal, which results in a denser, less sluble crystal. The reactivity rate, a measure f the time required t neutralize a given amunt f acid, is slwer fr dlmitic limestne as cmpared with calcitic limestne (Nller et al., 1980). The Mg in dlmitic limestne als may influence the Ca absrptin mechanism in the intestine. The mvement f Ca against a cncentratin gradient in everted gut sacs f the rat, guinea pig and rabbit is depressed by Mg ins, suggesting a cmmn transprt mech- anism (Schacter and Rsen, 1959; Alcck and Maclntyr e, 1960). Particle size. The calcitic limestnes used in Exp. 2 were frm a single surce and varied nly in particle size. The gemetric mean diameters fr these limestnes varied frm.11 t.40 mm. Hwever, the bne strength and bne ash values f pigs fed the three limestnes were very similar t the values btained fr the CaCO3 standard. Thus, the relative availability f the Ca in the three surces was similar (96 t 102%). These results agree with research by Pnd et al. (1981), wh fund that particle size f a calcitic limestne frm a single surce had little influence n the biavailability f Ca in the grwing pig. The particle sizes f the limestne that these investigatrs tested were apprximately the same as thse used in ur study. The marble dusts used in Exp. 4 and 5 varied in gemetric mean diameter frm.11 t.32 mm. Hwever, the Ca availability estimates fr the three marble dusts were similar (95, 98 and 100%). The gemetric mean diameter f the tw aragnites used in Exp. 5 was.17 and.54 mm, respectively, yet there was n evidence that the Ca in the finer material was any mre available (93%) than the Ca in the carser material (102%). The results f ur research indicate that, fr mst Ca surces, particle size (within the range tested in these trials) has very little influence n the bilgical availability f Ca. The effects f particle size n Ca biavailability in dlmitic limestne is less clear. The availability f Ca in the dlmite used in Exp. 3 was 78%, while in Exp. 4 the availability f Ca was 51%. The gemetric mean diameter f the dlmite in Exp. 3 was.06 ram, while the gemetric mean diameter f the dlmite in Exp. 4 was.24 mm. The larger particle size f the dlmite used in Exp. 4 may have cntributed t its lwer availability f Ca; hwever, this cannt be cmpletely delienated because the tw dlmitic limestnes were nt frm the same surce. Literature Cited Alcck, N. and I. Maclntyre Interrelatin f calcium and magnesium absrptin. Bichem. J. 76:19. ASAE Methd f determining and expressing fineness f feed materials by sieving. American Sciety Agricultural Engineer's Technical Cmmittee. Agricultural Engineers Yearbk. p 381. Besancn, P. and L. Gueguen. i969. Les principales

10 134 ROSS ET AL. vies due metablisme calcique chez le prc en crissance. Ann. Bil. Anita. Bichem. Biphys. 9:537. Byntn, R. S Chemistry and Technlgy f Lime and Limestne. Jhn Wiley and Sns, Inc., New Yrk. Cmbs, G. E. and H. D. Wallace Grwth and digestibility studies with yung pigs fed varius levels and surces f calcium. J. Anita. ScL 21:734. Crmwell, G. L., V. W. Hays, C. W. Scherer and J. R. Overfield Effects f dietary calcium and phsphrus n perfrmance and carcass, metatarsal and turbinate characteristics f swine. J. Anim. ScL 34:746. Dilwrth, B. C., E. J. Day and J. E. Hill Availability f calcium in feed grade phsphates t the chick. Pul. Sci. 43:1132. Eggert, R. C., W. T. Akers and C. N. Huhtanen Chlrtetracycline absrptin and calcium utilizatin in grwing swine as affected by terephthalic acid and calcium surce. J. Anim. Sci. 18:1505 (Abstr.). Hansard, S. L., W. A. Lyke and H. M. Crwder Absrptin, excretin and utilizatin f calcium by swine. J. Anita. ScL 20:292. Hayes, S. H., G. L. Crmwell, R. S. Stahly and T. H. Jhnsn Availability f phsphrus in crn, wheat and barley fr the chick. J. Anim. Sci. 49:992. McCampbell, C. W. and C. E. Aubel Calcium carbnate vs. calcium sulphate in swine ratins. Prc. 27th Annu. Meet. Amer. Sc. Anim. Prd. p 189. Miracle, G. L., G. L. Crmwell, T. S. Stably and D. D. Kratzer Availability f phsphrus in crn, wheat and sybean meal fr pigs. J. Anim. Sci. 45(Suppl. 1): 101. Nelsn, R. S. and A. C. Walker The bilgical evaluatin f phsphrus cmpunds. Pul. Sci. 43:94. Nller, C. H., J. L. White and W. E. Wheeler Characteristics f cement kiln dusts and animal effects. J. Dairy Sci. 63:1947. NRC Nutrient Requirements f Dmestic Animals, N. 2. Nutrient Requirements f Swine. Eighth Revised Ed. Natinal Academy f Sciences - Natinal Research Cuncil, Washingtn, DC. Owens, F. N Buffers and neutralizers in beef cattle. Buffers, Neutralizers and Electrlytes Sympsium. Natl. Feed Ingred. Assc., Des Mines, IA. Pnd, W. G., J. Yen, D. Hill and W. Wheeler Dietary calcium surce and level: Effects n weanling pigs. J. Anim. Sci. 53(Suppl. 1):91. Reid, B. L. and C. W. Weber Calcium availability and trace mineral cmpsitin f feed grade calcium supplements. Pul. Sci. 55:600. SAS SAS User's Guide. Statistical Analysis System Institute, Inc., Cary, NC. Schacter, D. and S. M. Rsen Active transprt f calcium by the small intestine and its dependence n vitamin D. Amer. J. Physil. 196: 357. Steel, R.G.D. and J. H. Trrie Principles and Prcedures f Statistics. McGraw-Hill Bk C., New Yrk. Stber, C. R., G. L. Crmwell and T. S. Stably Availability f phsphrus in crn and barley fr the pig. J. Anita. Sci. 49(Suppl. 1):97. Thmas, B. H., C. C. Culbertsn, J. M. Ramsbttm and W. E. Hammnd The cmparative efficacy f "Dicaph", bne meal and limestne when fed as mineral supplements t ratins fr pigs Prc. 26th Annu. Meet. Amer. Sc. Anita. Prd. p 142. Waldrup, P. W., C. B. Ammerman and P. H. Harms The utilizatin by the chick f calcium frm different surces. Pul. Sci. 43:212.