Composition and Nutritive Value of Ground Sea Clam Shells as Calcium Supplements for Lactating Holstein Cows1

Composition and Nutritive Value of Ground Sea Clam Shells as Calcium Supplements for Lactating Holstein Cows1 A. D. FINKELSTEIN, J. E. WOHLT, and S. M. EMANUELE Department of Animal Sciences Rutgers-The State University New Brunswick, NJ 08903 S. M. TWEED New Jersey Marine Advisory Service Cape May Court House, NJ 08210 ABST.RACT

and 33.9%; and fecal pH, 6.31, 6.31, 6.45; respectively. Data support that sea clam shells reduced to the particle size utilized in this study can serve as effective Ca supplements for lactating dairy cows. (Key words: calcium supplements, sea clam shells, lactation)

Ocean quahog and surf clam shells were evaluated as Ca supplements with aragonite as a reference standard. Shells obtained directly after processing were dried, and particle size was reduced through a jaw crusher and disc grinder. Calcium, total acid-consuming capacity, and rate of reactivity (pH 6 and 3) for aragonite, ocean quahog, and surf shell were 39.2, 38.5, and 36.4%; 19.8, 18.8, and 18.4 meq/g; >9, >9, and 3.5 h at pH 6; and 43, 38, and 20 min at pH 3; respectively. Particle size was determined by dry sieving with 75, 80, and 55% of aragonite, ocean quahog, and surf shell >150 /l. Shell characteristics contributed to variation in particle size. Each Ca source provided approximately 65% of Ca intake for three midlactation Holstein cows fed a com silage and concentrate (1:1, DM basis) diet in a 3 x 3 Latin square design for 4 wk. Cows fed aragonite, ocean quahog, and surf shell averaged DMI, 20.3, 21.6. and 22.6 kg/d; milk yield, 26.9. 28.8, and 28.3 kg/d; milk fat, 4.23, 4.17, 4.03%; milk protein, 3.48, 3.32, and 3.40%; apparent digestibility of OM. 72.5. 71.7, and 72.0%; apparent digestibility of Ca, 20.6, 31.5,

Abbreviation key: OQCS = ocean quahog clam shell, SCS = surf clam shell. INTRODUCTION

Received June 22, 1992. Accepted October 28, 1992. INew Jersey Agricultural Experiment Station Publication Number 0-06901-2-92, supported by NJAES sustainable agriculture and New Jersey Fisheries and Aquaculture Technology Extension Center funds. Financial support also was provided by Borden, Inc., Columbus, OH and the Gorton Group, Gloucester, MA. 1993 J Dairy Sci 76:582-589

The mid-Atlantic region produces over 65% of the total US sea clam harvest (3, 9). Species of sea clams harvested include ocean quahog clam (Arctica islandica) and surf clam (Spisula solidissima). The shell represents approximately 83% of the solid waste produced by the sea clam processing industry. Current uses for sea clam shells are limited to fill and liner for roads and ditches. Future environmental regulations may require alternative options for shell disposal (3, 9). Oyster shell has been used extensively as a Ca supplement in the poultry industry (10, 11, 12). In theory, sea clam shell could be a suitable CaC03 source for both ruminants and nonruminants. Muir et a1. (12) found sea clam shells to be a suitable Ca supplement for laying hens. However, no published data are available on the use of sea clam shells as Ca supplements for ruminants. Therefore. samples of freshly processed and stockpiled ocean quahog clam shells (OQCS) and surf clam shells (SCS) were ground, and nutrient content, particle size, buffering capacity. and rate of reactivity were compared with that of aragonite. In vivo studies also were conducted with ground freshly processed

582

CALCIUM SUPPLEMENTS

OQCS and SCS to determine the effects on feed intake, milk yield and composition, nutrient digestibility, and Ca balance in midlactation cows. MATERIALS AND METHODS Ca Supplements

Aragonite, provided courtesy of the Limestone Products Corp. (Sparta, NJ), served as a reference source of feed grade CaC03. The OQCS and SCS were obtained immediately upon exit from the processing facilities at Borden, Inc. (Cape May, NJ) and Cape May Canners (Cape May, NJ), respectively. Samples of OQCS and SCS also were obtained from land stockpiles (> 1 yr) to provide a comparison of freshly processed versus stockpiled shell (Table 1). This study required 70 kg of each shell type. Perimeters of processor and land stockpiles were sampled, and a single composite was produced. Use of the production facilities of Limestone Products Corp. was unfeasible because amounts of shell to be ground at one time were too great. Thus, to produce a suitable amount and particle size of the Ca supplement, shells were first broken with a hammer, then jaw crushed (number 226; Denver Fire Clay Co., Denver, CO), and finally disc ground (Braun Pulverizer, Type VA; Braun Corp., Los Angeles, CA) using the laboratory facilities of Limestone Products Corp. Lactation and Balance Study

Three midlactation Holstein cows averaging 150 DIM were used in a 12-wk study in a 3 x 3 Latin square design. Each cow was fed one of three diets for 4 wk (Table 2). Each diet contained 96% corn silage and concentrate (1: I, DM basis) fed as a lMR and 4% long grass and legume hay (DM basis). Dietary treatments varied by source of supplemental Ca: 1) aragonite, 2) ground freshly processed OQCS, and 3) ground freshly processed SCS. Each supplement provided approximately 65% of the daily total Ca intake. Cows were kept in individual tie stalls but received 2 h of exercise daily in a drylot except during total fecal and urine collections. Cows were weighed for 3 consecutive d at the

583

end of each treatment period, and body condition was scored on a five-point scale, where 1 thin and 5 = fat. Milking occurred at 0500 and ]600 h, and yield was recorded. One-half of the daily TMR was fed at 0600 h, and the remainder of the TMR plus hay was fed at 1400 h. Orts were recorded prior to the next O600-h feeding. Concentrates and corn silage were sampled daily and hay weekly. Samples of feed were dried in a forced-air oven at 60·C, ground in a Wiley mill (I-mm screen; A. H. Thomas, Philadelphia, PA), composited within each treatment period, and stored in airtight containers until further analyses. Total fecal and urinary collections were performed on d 22 to 27 in each 4-wk period. Com silage, concentrates, and hay were fed as described. Orts were sampled at 0600 h the following day. Approximately I% of the orts were stored at 4·C until the end of collection, when a composite was made. Milk was sampled at each milking, composited by volume, and stored at -]5·C until analysis. During collection, cows were housed in tie stalls that contained no bedding. A 75-cc Foley catheter (c. R. Bard, Covington, GA) was placed in the bladder (4). Urine was collected and stored in polyethylene containers under acidic conditions (50 ml of 50% H2S04). Volume was recorded and sampled daily. At the end of the 6-d period, urine was composited by volume and stored at -15·C until analysis. Fecal production was measured daily, pH was determined, and a portion was stored at 4·C with thymol as a preservative. The feces were composited at the end of 6 d, dried in a forcedair oven at 60T, and ground in a Wiley mill.

=

Laboratory Analyses

Particle size of all Ca sources was determined by dry sieving (Rotap; courtesy of Limestone Products Corp.) and expressed as the percentage passing through screens with various meshes (Table 1). Standard methods (2) were used to measure DM and CPo Sources of Ca were titrated with acid to determine acid-consuming capacity and rate of reactivity in vitro (5, 14, 19, 20). Mineral analysis included both macroelements (Ca, CI, Mg, P, Na, and S) and microelements (As, B, Cd, Cr, Cu, Fe, I, Pb, Si, and Zn) by the research laboratories of Min-Ad, Inc. (Greeley, CO) and Agway Inc. (Ithaca, NY). Composite samples Journal of Dairy Science Vol. 76. No.2. 1993

584

FINKELSTEIN ET AL.

of concentrates, corn silage, hay, oris, and feces were analyzed for DM (2), starch (17), and Ca (15).

Milk protein (Udy method) and fat (Babcock method) were determined using standard procedures (2). Milk proteins were precipitated

TABLE 1. Nutrients, particle size, acid-consuming capacity, and rate of reactivity of aragonite and ground sea clam shells. Sea clam shell

Ocean quahog Aragonite DM,4 0/0 CP, % Carbonate,5 % CaC03 MgC03 Minerals, % Ca Mg K Na CI P Si S Minerals, ppm As B

Cd Cr Cu Fe Hg I Pb Zn Particle size,6 % passing mesh diameter 1190 p. 600 p. 300 p. 150 p. 75 p. 45 p. 38 p. Total acid consuming capacity,7 rneq of H+ pH Slat titration. 7 half-life pH 6.0, h pH 3.0, min

Processed l

Stockpiled2

Surf Processed 3

Stockpiled 2

99.53 0

95.18 1.75

99.57 1.05

89.86 1.70

99.10 .70

96.31 3.49

95.73 4.19

95.93 3.87

91.65 5.67

93.59 4.81

39.18 .17 .08 .33 .10 <.01 .29 .12

38.50 .02 .07 .53 .06 <.01 1.02 .10

38.30 .02 .06 .50 .04 <.01 .77 .08

36.35 .03 .08 .69 .12 .01 3.45 .10

38.79 .02 .07 .52 .02 .01 2.40 .08


<1 <10 <1 13 18 20 <1 8.9 1.2 <5

<1 <10 <1 6 22 32 <1 8.8 1.1 <5


<1 <10 <1 9 7 22 <1 6.6 .7 <5

100 99.6 81.1 24.1 9.8 7.4 6.2

95.8 62.1 34.7 20.1 13.0 10.8 9.9

91.0 53.0 29.7 18.4 12.6 10.6 9.7

98.3 80.0 60.4 44.7 33.7 29.3 26.6

86.6 53.5 34.1 23.4 17.5 15.0 13.5

19.8

18.8

19.4

18.4

16.8

>9 43

>9 38

>9 41

3.5 20

6.5 26

IObtained directly from processing line at Bordens, Inc. (Cape May, NJ). 2Previously processed clams that were stockpiled. 30btained directly from processing line at Cape May Canners (Cape May. NJ). 4As received. 5Standards ASTM (I) courtesy Limestone Products Corp. (Sparta, NJ). 6Rotap. sieve analysis. Courtesy of Limestone Products Corp. 7Courtesy of Min-Ad, Inc. (Greeley, CO). Journal of Dairy Science Vol. 76, No.2, 1993

585

CALCIUM SUPPLEMENTS

RESULTS AND DISCUSSION

with TCA prior to the determination of milk Ca (20).

Ca Sources Statistical Analysis

Milk yield and composition, DMI, nutrient digestibility, and Ca balance data were analyzed by ANOVA using the general linear models procedure of SAS (16). Main effects in the model included treatment, which was the type of Ca source (aragonite vs. OQCS vs. SCS), period, and cow. Results were considered to be significant when the probability associated with the mean comparison was P < .05 unless otherwise noted.

Limestone and CaC03 by definition (13) should contain not less than 33 and 38% Ca, respectively. Freshly processed and stockpiled OQCS and SCS were relatively pure sources of CaC03, containing 92 to 96% CaC03 and 36 to 38% Ca (Table 1). Aragonite, a precipitate of dissolved Ca salts from shelled marine life, is already mined from the ocean floor and used currently in animal, plant, and chemical industries requiring a pure source of CaC03. In a previous study (20), aragonite was compared

TABLE 2. Composition of the diets varying in Ca source fed to midlactation dairy cows. Sea clam shelP Items

Aragonite

Ocean quahog

Surf

(% of OM)

Forage Com silage Hay Concentrate, % of total Soybean meal Com meal Crimped oats Distillers grains Molas-Nutra2 Wheat bran Wheat middlings Beet pulp Monosodium phosphate Salt Magnesium oxide Vitamin E 20,0003 Vitamin ADE IX4 Potassium sulfate Dairy trace minerals s Aragonite Ocean quahog shell Surf shell

48 4

48 4

48 4

14.80 11.78 4.24 4.01 3.52 2.82 2.07

14.80 11.75 4.24 4.01 3.52 2.82 2.07 1.77 .90 .18 .16 .05 .03 .03 .02

14.80 11.66 4.24 4.01 3.52 2.82 2.07 1.77 .90 .18 .16 .05 .03 .03

1.77 .90 .18 .16 .05 .03 .03

.02

.02

1.62 1.65 1.74

Minerals,6 %

Ca

.73

P Mg

.45

.83 .47 .22

.23

.88 .51 .24

lObtained directly from processors, dried and ground. 2Cane molasses product containing 2:73% OM. 3Each kilogram contains 44,000 IU of vitamin E. 4Each kilogram contains 8.8 million IU of vitamin A, 2.2 million IV of vitamin 0, and 33,000 IU of vitamin E. 5Each kilogram contains 15% Zo, 4% Mn, .7% Fe, .5% Ca, .3% I, .08% Co, and 546 ppm of Se. 6Based on chemical analyses of corn silage, hay, and concentrate samples. Journal of Dairy Science Vol. 76, No.2, 1993

586

FINKELSTEIN ET AL.

with calcite flour (limestone) and albacar (precipitated CaC0 3) and determined to be equal, if not superior, to calcite flour as a Ca source for lactating dairy cows. Therefore, aragonite was selected over limestone as the reference CaC03 for in vitro and in vivo evaluations of OQCS and SCS. Aragonite and stockpiled sources of OQCS and SCS contained
ing equipment is unknown. Both OQCS and SCS. fresh or stockpiled, contained approximately threefold more I than did aragonite. Amounts of heavy metals in aragonite, OQCS, and SCS were similar (Table 1). Because of low content and feeding rate, supplemental Ca sources would contribute little to intake of heavy metals and would be within NRC (13) recommendations for lactating dairy cows. Aragonite had a very selected particle size; a major portion of the sample ranged between 150 and 300 J1. in diameter (Table 1). Freshly processed SCS had finer particle size than either type of OQCS or stockpiled SCS (Table 1). Because the same methodology was used to prepare and to grind fresh and stockpiled OQCS and SCS, variation in particle size of the final product may have been the result of differences in shell properties. The SCS were larger and more oblong than the OQCS. Fresh SCS were more difficult to break with a hammer and splintered into jagged pieces compared with OQCS. The fresh SCS also required more grinding than did OQCS, probably because of sheIl properties and the longer retention of the particles within the disc grinder. With stockpiling, the sheIl may age and become more brittle. Stockpiled SCS tended to have grinding time and particle size similar to that of OQCS. Total acid-consuming capacity of OQCS and freshly processed SCS was similar to that of aragonite (Table 1), but lower for stockpiled SCS. Rate of reactivity, as determined by pH stat titration, was similar for OQCS and aragonite at pH 6 and 3 (Table I), which is representative of a slowly reactive CaC03 source (8, 19, 20). In contrast, SCS, both freshly processed and stockpiled, were faster reacting CaC03 sources. Titration curves depicting titratable acidity and buffering capacity of the Ca sources tended to paraIlel one another (Figure 1) although freshly processed and stockpiled SCS tended to provide greater buffering capacity. Reduced particle size may have been a major factor contributing to the increased rate of reactivity and buffering capacity of SCS (19). Intake and Lactation Performance

The availability and cost of land and the enactment of environmental regulations may

587

CALCIUM SUPPLEMENTS

TABLE 3. The OMI, milk yield and composition, BW, and body condition scores of midlactation dairy cows fed aragonite or sea clam shells'! Sea clam shell

OMI, kgld Milk yield, kgld Milk protein, % Milk fat, % BW, kg Body condition 2 In

Aragonite

Ocean quahog

Surf

20.3 26.9 3.48 4.23 582 3.0

21.6 28.8 3.32 4.17 594 3.2

22.6 28.3 3.40 4.03 600 3.2

SE .5 .6 .05 .12 15 .1

= 3.

2Five-point scale (I = thin to 5

= fat).

limit or prohibit future stockpiling of OQCS and SCS. Immediate use of processed OQCS and SCS may be required and furthermore, the in vitro similarities between freshly processed and stockpiled shells resulted in feeding freshly processed OQCS and SCS to lactating dairy cows. Cows readily consumed all diets containing ground freshly processed OQCS and SCS. Reported DMI and milk yield means represent averages of wk 3 and 4 of each period. The DMI ranged from 20.3 to 22.6 kg/d and was lowest for cows fed aragonite and greatest for cows fed OQCS and SCS even when expressed as a percentage of BW (3.5 vs. 3.8%). These differences were not significant (P > .05) (Table 3). Milk yield and composition were similar among Ca sources and averaged 28 kgld of milk yield, 4.1 % milk fat, and 3.4% milk protein (Table 3). Milk yield paralleled DMI and was greater for cows fed OQCS and SCS. Body weight and condition scores also paralleled DMI and tended to be greater for cows fed OQCS and SCS (Table 3).

elicit a response, as when aragonite and albacar (average particle size, 420 vs. 2 p.; half-life at pH 3, 40 vs. <1 min) were fed in a previous study (20). Ca Utlllzation

Calcium intake varied from 129.1 to 191.7 gld (P < ,08) and was less for cows fed aragonite. The lower Ca intake by cows fed aragonite was due, in part, to a combination of less Ca present in the diet (Table 2) and a lower DMI by cows (Table 3). All feeds and

00 , . . - - - - - - - - - - - - - - - - - ,

--

Aragonite

•.•.••.•.•.

Sur!

Fecal pH and Nutrient Digestibility

Physical properties of supplemental Ca sources have been implicated as affecting fecal pH and digestibility of DM and starch because of modifications in digestive tract physiology (13, 20). Although particle size and rate of reactivity varied among aragonite, OQCS, and SCS (Table I), wet fecal pH (6.31 to 6.45) and digestibility of DM (71 to 72%) and starch (93 to 96%) did not differ for cows fed these Ca sources (Table 4), suggesting that the difference in physical properties between aragonite and OQCS and SCS was not large enough to

3+---~~-...,....---r---~--~

o

Hel, meq

Figure I. The milliequivalents of acid (.IN HCI) added to Ca supplements (aragonite, ocean quahog, and surf clam shells) until the pH was decreased to 4. Journal of Dairy Science Vol. 76, No.2, 1993

588

FINKELSTEIN ET AL.

TABLE 4. Wet fecal pH, nutrient digestibility, and Ca balance in midlactation Holstein cows fed aragonite or ground sea clam shells. Sea clam shell Aragonite Fecal pH Apparent digestibility, % DM Starch Ca True digestibility.] % Ca Ca Balance. gld Intake Feces Urine Milk Retained B.bp

c.dp

6.31

Ocean quahog 6.31

Surf 6.45

SE .03

72.5 94.1 20.6

71.7 95.g 31.5

72.0 92.6 33.9

1.1 2.6 4.6

27.6

36.g

38.7

4.2

129.lb lOO.9d .5 33.4 -5.7

178.5" 116.2cd .6 35.g 25.9

191.7" 126.9c .5 33.4 30.9

10.0 2.4 <.1 1.7 11.5

< .08. < .05.

lCalculated by assuming endogenous loss of 1.54 g of Cal100 kg of BW (13).

supplements were analyzed for Ca, and variation in content was taken into account prior to diet formulation for .9% Ca. A decreased Ca in the concentrate portion of the aragonite treatment was unanticipated and cannot be readily explained. Fecal Ca ranged from 100.9 to 126.9 gld (Table 4) and was lower for cows fed aragonite. Nevertheless, cows fed aragonite had a higher proportional loss of Ca via feces (fecal Ca as a percentage of Ca intake was 78% for cows fed aragonite vs. 66% for those fed either OQCS or SCS). Apparent digestibility of Ca tended to be lower (21 vs. 33%) for cows fed aragonite than for cows fed OQCS or SCS (Table 4). Calculation of true digestibility of Ca resulted in the same trend: aragonite digestibility was less than that of OQCS or SCS (28 vs. 38%), because BW were similar across treatments (Tables 3 and 4). When aragonite, calcite flour, and albacar were previously used as Ca supplements for lactating dairy cows (20), apparent digestibilities of Ca averaged 40, 26, and 34%, respectively. The NRC (13) currently assumes that Ca is 38% available for the adult dairy cow. In studies with lactating dairy cows (7, 18), average availability of Ca ranged from 35 to 38%. In general, the average availability of Ca from concentrate, forage, and limestone is assumed to be 43, 35, and 38% (13). However, when Journal of Dairy Science Vol. 76. No.2. 1993

Hansard et al. (6) varied source of supplemental Ca, true absorption of Ca ranged from 37 to 55% in adult cattle. Given that OQCS and SCS supplied 65% of dietary Ca and that the true absorption of dietary Ca was 38%, OQCS and SCS can very likely serve as effective sources of Ca supplement for lactating dairy cows. Calcium excretion in urine and milk averaged .5 and 34 gld (Table 4), respectively, and did not differ significantly among treatments. Calcium retention was positive for cows fed OQCS and SCS (26 to 31 g/d) but was negative for cows fed aragonite, based on apparent fecal Ca losses (Table 4). According to the NRC (13), cows utilized in this study (Table 3, 590 kg of BW; milk yield, 28 kgld; milk fat, 4.2%) require 114 gld of Ca. The Ca intake on all dietary treatments exceeded that amount (Table 4), but data suggest that diets consisting primarily of corn silage and concentrate (Table 1) require higher Ca content and Ca availability >30%. CONCLUSIONS

Properly dried and ground OQCS and SCS contain high percentages of Ca (>36%) that are available to the ruminant. Buffering capacity can vary in response to particle size, which may depend on shell properties exhibited dur-

CALCIUM SUPPLEMENTS

ing grinding. The data suggest that OQCS and SCS are equivalent to aragonite as a Ca source for dairy cattle. ACKNOWLEDGMENTS

The authors thank the following individuals for their interest and assistance in conducting the study: Alan Van Gelder of Limestone Products Corp.; Reg Whitson of Min-Aid, Inc.; and farm employees, Joyce Farkas, Bill O'Hare, Denise Palatine, and Pegi Zajac of the Department of Animal Science. REFERENCES

1 Annual Book of ASTM Standards. Vol. 4.01., ASTM, Easton. MD. 2 Association of Official Analytical Chemists International. 1990. Official Methods of Analysis. 15th ed. AOAC, Arlington, VA. 3 Boardman, G. D., G. 1. Flick, and E. L. Lihelo. 1989. Characterization and utilization of waste from ocean quahog and surf clam processing plants. Civil engineering section. A report. Mid-Atlantic Fisheries Dev. Found., Inc., Annapolis, MD. 4 Crutchfield. W. O. 1968. A technique for placement of an indwelling catheter in the cow. Vet. Med. Small Anim. Clin. 63:1141. 5 Jasaitis. D. K., J. E. Wohlt. and J. L. Evans. 1987. Influence of feed ion content on buffering capacity of ruminant feedstuffs in vitro. J. Dairy Sci. 70:1391. 6 Hansard, S. L., C. L. Crowder, and W. A. Lyke. 1957. The biological availability of calcium in feeds for callie. 1. Anim. Sci. 16:437. 7 Hibbs, 1. W., and H. R. Conrad. 1983. The relation of calcium and phosphorus intake and digestion and the effects of vitamin D feeding on the utilization of calcium and phosphorus by lactating dairy cows. Res. Bull. 1150, Ohio Agric. Exp. Stn., Wooster. 8 Keyser, R. B., C. H. NoUer, L. J. Wheeler, and D. M. Schaefer. 1985. Characterization of limestones and

589

their effects in vitro and in vivo in dairy cattle. 1. Dairy Sci. 68:1376. 9 Lopez, R. A., and N. R. Henderson. 1989. Impediments to increased agricultural and seafood processing in New Jersey. New Jersey Agric. Exp. Stn. Pub\. No. R-02261-1-88, New Brunswick. 10Makled, M. N., and O. W. Charles. 1987. Eggshell quality as in fluenced by sodium carbonate. calcium source and photoperiod. Poult. Sci. 66:705. 11 Moran, E. T., Jr., A. Eyal, and 1. D. Summers. 1970. Effectiveness of extra-dietary calcium supplements in improving egg shell quality and the influence of added phosphorus. Poult. Sci. 49: 1011. 12 Muir, F. V.• P. C. Harris. and R. W. Gerry. 1976. The comparative value of five calcium sources for laying hens. Poult. Sci. 55:1046. 13 National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th rev. ed. Natl. Acad. Sci., Washington, DC. 14 Noller, C. H., and J. L. White. 1980. Analytical techniques for evaluating reactivity of limestone. Feed Manage. 31:34. 15 Perkin-Elmer Corporation. 1971. Analytical Methods for Atomic Absorption Spectrophotometry. PerkinElmer Corp., Norwalk, CT. 16 SAS~ User's Guide: Statistics, Version 5 Edition. 1985. SAS Inst., Inc., Cary. NC. 17 Smith, D. 1969. Removing and analyzing total nonstructural carbohydrates from plant tissues. Page 1 in Wisconsin Agric. Exp. Stn. Rep. 41, Madison. 18 Ward, G., R. C. Dobson, and J. R. Dunham. 1972. Influence of calcium and phosphorus intakes, vitamin D supplement, and lactation on calcium and phosphorus balances. 1. Dairy Sci. 55:768. 19 Wohlt. J. E., D. K. Jasaitis, and J. L. Evans. 1987. Use of acid and base titrations to evaluate the buffering capacity of ruminant feedstuffs in vitro. J. Dairy Sci. 70:1465. 20 Wohlt, J. E., D. E. Ritter, and J. L. Evans. 1986. Calcium sources for milk production in Holstein cows via changes in dry matter intake. mineral utilization and mineral source buffering potential. J. Dairy Sci. 69:2815.

Journal of Dairy Science Vo\. 76, No.2, 1993