Magnesium in Limestones for Laying Chickens

853

EDIBLE YIELD OF TURKEY PARTS

TABLE 9.—A verage percent of total carcass contributed by the different edible and inedible components Component Meat

Bone

Tendon

Skin

Fresh Carcass

72.6

18.4

0.7

8.3

Cooking Method Hot Water Bath Pressure Cooked*

48.1 45.1

13.2 11.4

0.4 0.4

7.8 5.3

Broth

23.6

Volatile Cooking Loss

Total Cooking Loss

14.4

30.4 38.0

* Without giblets.

SUMMARY AND CONCLUSIONS Twelve market torn turkey carcasses were divided into 10 parts. Two turkeys were boned fresh, while five were boned after pressure cooking and five after cooking in a hot water bath. The parts were divided into meat, bone, skin, and tendon, with edible and inedible yields computed. Cooking loss was measured on the cooked parts. The breast and thighs accounted for approximately 57 percent of the total carcass weight and 65 percent of the total edible meat. The neck was about 4.5 percent of the total carcass, 40 to 60 percent edible meat, and yielded about 4 percent of the total carcass meat. The "rack" or "cage" yielded 9 to 10

percent of the total carcass meat but was difficult to bone. Pressure cooking resulted in a significantly higher cooking loss than cooking in a hot water bath. The breast and rib back had significantly higher volatile cooking loss than other parts of the carcass. REFERENCES Buss, E. G., and T. E. Hartung, 1954. Unpublished data. Colorado Agr. Expt. Sta. Fry, J. L., O. S. Rao and L. D. Rasplicka, 1962. Factors affecting the yields of turkey parts. Poultry Sci. 4 1 : 1299-1303. Goertz, G. E., A. S. Hooper and J. L. Fry, 1962. Edible yield of roasted breasts, thighs of Bronze and White turkeys. Poultry Sci. 4 1 : 1295-1298. Winter, A. R., and P. Clements, 1957. Cooked edible meat in ready-to-cook poultry. J. Amer. Diet. Assn. 33: 800-802.

Magnesium in Limestones for Laying Chickens ARNON L. MEHRING, JR. AND DEWEY JOHNSON, JR. 1 Lime Crest Research Laboratory, Limestone Products Corporation of America, Newton, New Jersey (Received for publication November 4, 1964)

T

HE BELIEF that additions of magnesium to the diet of laying chickens is likely to produce adverse effects and should be avoided, became established very early in the history of poultry nutrition. 1 Present address: Equitable Life Assurance Society of the United States, New York, New York.

Alder (1927) reported that the use of freechoice dolomite as the only grit for Leghorn pullets resulted in decreased production, progressively thinner egg shells, and diarrhea within a period of four months. Replacing the dolomite with a high-calcium limestone corrected these ill effects. He concluded: "Since magnesium forms a part of most deposits of limestone, this

854

A. L. MEHRING, JR. AND D. JOHNSON, JR.

product should never be used unless it is cal-type diet containing about 2,200 p.p.m. found to be free from this element." of magnesium. Wheeler (1919) and Walker (1949) demSupplee (1963) reported that no adverse onstrated that magnesium will not satisfac- effects on egg production, efficiency of feed torily replace calcium in the diet of the utilization, egg weight, shell thickness, or laying chicken. shell strength were observed when he inAdverse effects on growth and bone de- creased the level of dietary magnesium to velopment of chicks were noted by Buck- 2,200, 2,500, 3,500, 5,500, and 9,000 ner et al. (1932) when very high levels of p.p.m. by the addition of magnesium carmagnesium carbonate (1.36 to 1.48 percent bonate. The maximum addition of magmagnesium) were added to the diets of nesium was 7,300 p.p.m. At this level, growing chicks. It was reasoned by many there was a slightly greater amount of that additions of this element to the diet of moisture in the excreta. laying chickens should be avoided. Staller and Sunde (1964) fed laying Nevertheless, there were some early re- chickens a practical diet supplemented ports that indicated that additions of mag- with either dolomitic limestone or magnesinesium to the diet are not necessarily um carbonate in sufficient quantity to proharmful. Tully and Franke (1934) com- vide dietary levels of magnesium of 3,300, pared oyster shell, clam shell, chalkstone, 4,800, 7,600, and 13,300 p.p.m. During Black Hills limestone, dolomite limestone, eight months, egg production and egg calcite, and a commercial limestone as weight were not depressed as a result of sources of calcium. They observed no any of the levels of magnesium. The dry significant differences in egg production, matter in the excrement decreased with inegg weight, or breaking strength of the creases in the dietary levels of both mageggs as a result of using these several nesium carbonate and dolomitic limestone, sources of calcium; but they did observe a but the decrease was not so pronounced mild diarrhea in those chickens receiving with the increases of dolomitic limestone. the dolomite. Modern layer diets usually contain more Branion (1947) reported observing no calcium than formerly, and may contain ill effects in laying chickens when all the more magnesium as well if limestones concalcium, other than that present in the taining magnesium are used as a source of grains and protein supplements, was fur- calcium. The experiments reported in this nished by dolomitic limestone of "fairly paper were conducted to observe the effects high magnesium carbonate content." Even of the magnesium in the limestone when when similar levels of magnesium as mag- diets containing as much as 3.0 and 4.0 nesium carbonate were added to the basal percent of calcium are fed. diet, no ill effects were observed. EXPERIMENTAL PROCEDURE Recent experiments indicate that laying Three experiments of 48 weeks duration chickens are more tolerant of additions of magnesium to the diet than had been gen- each were conducted in three successive erally believed. Halloran et al. (1961) re- years. Each experiment was started with ported an actual improvement in egg pro- 192 pullets just beginning to lay. New duction in four of five experiments in Hampshires were used in the first two which up to 485 p.p.m. of magnesium, as experiments; White Leghorns, in the third. magnesium oxide, was added to a practi- In each experiment, the pullets were as-

855

MAGNESIUM IN LIMESTONE FOR LAYERS

signed to 12 groups of 16 each, according to a restricted, randomized distribution, so that the live weights of the pullets of each group were as nearly as possible like the weights of the pullets of each of the other groups. The pullets were put into batteries of individual cages, the locations of the cages being such that the individuals of each group were approximately equally distributed (1) at all levels in the batteries, (2) on both sides of the batteries, and (3) among the several batteries of cages. The chickens were kept in a room without windows. The temperature of the room was held at 65 ± 2°F. and the relative humidity was kept at 50 ± 5 percent Artificial illumination was provided for a 14-hour period in each day throughout the first and third experiments, and for the first 18 weeks of the second experiment. In the latter experiment, the period of daily illumination was increased by 8 minutes per week from the 18th to the 48th week. By the end of the experiment, the daily period of illumination had been lengthened to 18 hours. The experimental treatments consisted of feeding diets that contained limestones or simulated limestones of different content of magnesium. There were three replicates of each treatment in each experiment. In Experiment 1, U.S.P. calcium carbonate was used to supply the calcium in one of the diets, and calcite flour was used in the other three. Graded additions of U.S.P. magnesium oxide were made along with the calcite flour to simulate limestones of different content of calcium and magnesium. The ratios of the magnesium carbonate equivalent of the magnesium to the calcium carbonate equivalent of the calcium in the calcium carbonate and in the combinations of calcite flour and magnesium oxide were 0:100, 9:91, 18:82, and

TABLE 1.—Formulas of the diets of Experiment 1 Diet

Ground yellow corn Soybean meal (44% protein) CaCOa (U.S.P.) Calcite flour MgO (U.S.P.) Glucose monohydrate Corn oil Dicalcium phosphate Salt Combination of minor ingredients^ Totals

0:100

9:91

18:82

27:73

Percent 64.74

Percent 64.74

Percent 64.74

Percent 64.74

21.99 6.95

21.99

21.99

21.99

— — 3.46 1.56 .38 .50 .42

7.70 .07 2.11 2.09 .38 .50 .42

7.70 .47 1.44 2.36 .38 .50 .42

7.70 .97 .62 2.68 .38 .50 .42

100.00

100.00

100.00

100.00

—

—

—

a This refers to the ratio of the magnesium carbonate equivalent of the magnesium to the calcium carbonate equivalent of the calcium in the CaC03 (U.S.P.) and in the mixtures of calcite flour and MgO (U.S.P.). b Supplied per kilogram of diet: 60 mg. manganese, 1.2 mg. iodine, 20 mg. iron, 2 mg. copper, 0.2 mg. cobalt, 0.1 rag. zinc, 369 mg. choline, 7,200 I.U. vitamin A, 6.6 meg. vitamin B12, 802 I.C.U. vitamin D3, 7.36 mg. pantothenic acid, 3.0 mg. riboflavin, 1.26 mg. vitamin K.

27:73. The latter ratio is similar to that of some dolomitic limestones. The formulas of these diets are given in Table 1. In Experiments 2 and 3, a high-calcium limestone (38.8% Ca, 0.385% Mg) and a high-magnesium limestone (26.9% Ca, 6.43% Mg) were used alone and in combinations, instead of the U.S.P. magnesium oxide, to provide the same ratios of magnesium carbonate equivalent to calcium carbonate equivalent that were used in Experiment 1. There was a small quantity of magnesium in the high-calcium limestone, however, and the ratio in this product was actually about 1:99 rather than 0:100. The high-magnesium limestone did not contain quite enough magnesium to provide a ratio of 27:73, so it was supplemented with a small amount of U.S.P. magnesium oxide to provide the desired ratio. The diets were mixed at intervals of 12 weeks. Before each batch of feed was mixed, chemical analyses were made of the ingredients and of the combination of minor ingredients for protein, fat, fiber,

856

A. L. MEHRING, JR. AND D. JOHNSON, JR.

ash, calcium, phosphorus, and magnesium. The metabolizable energy of the ingredients was calculated according to the procedure outlined by Titus (1961). On the basis of these analyses, the diets were formulated to contain the desired levels of the nutrients. All the diets in each experiment were formulated to contain 16.0 percent of protein by adjusting the proportion of corn and soybean meal. The energy content of the diets was held constant by adjusting the quantities of glucose monohydrate and corn oil as required. In Experiments 1 and 2, there were an estimated 2.93 kilocalories of metabolizable energy per gram of each diet. In Experiment 3, there were 2.87 kilocalories per gram. The diets of Experiments 1 and 2 were formulated to contain 3.0 percent of calcium and 0.4 percent of total phosphorus. The diets of Experiment 3 were formulated to contain 4.0 percent of calcium, and the quantity of dicalcium phosphate was adjusted so that the diets of half the chickens on each of the four principal treatments contained 0.35 percent of phosphorus and the diets of the other half contained 0.6 percent of phosphorus. After each batch of feed was mixed, chemical analyses were made to check the level of protein, calcium, phosphorus, and magnesium in each diet. The actual levels were very close to the intended levels. The average levels of magnesium, given in Table 2, covered a range from 1,640 p.p.m. to 11,515 p.p.m. Egg production was recorded daily, and each fourth egg laid by each chicken was weighed and tested for strength of shell in a device described by Mehring (1949). The chickens were manually inseminated with pooled semen, and all the suitable eggs not used for the determination of strength of shell were incubated at weekly intervals. The weights of the chickens and of the total feed consumed were obtained

TABLE 2.—Average levels of magnesium

in the diets* Diet Experi- Ratio of MgCOa to CaCOa in the calcium supplements'3 ment

1 2 3

P.p.m. P.p.m. P.p.m. 1,640+17 3,360±30 5,650+94 1,770+42 3,520±66 5,810+158 1,830+25 4,036±78 7,293+132

P.p.m. 8,380+86 8,370+246 11,515 + 210

*b By analyses. This refers to the ratio of the magnesium carbonate equivalent of the magnesium to the calcium carbonate equivalent of the calcium in the limestones or simulated limestones included in the diets.

at intervals of 28 days. After the eggs were sorted each week in preparation for incubation, each chicken's eggs, as a group, were given a score of 1 to 4, according to the smoothness of the egg shells. A score of 1 denoted very rough shells; 2, moderately rough shells; 3, slightly rough shells; and 4, normal, smooth shells. At four week intervals, the excreta of each chicken were scored for apparent dryness. A score of 1 denoted watery or liquid excreta; 2, very wet or pasty excreta; 3, normal, formed excreta; and 4, dry, wellformed excreta. All of the data for each chicken were summarized at four-week intervals, and the averages of the measures of performance of the chickens in each experimental group, and on each experimental treatment, were calculated. All of the data were analyzed for statistical significance. RESULTS AND DISCUSSION The averages of the measures of performance of the chickens for the 12 four-week periods in each of Experiments 1, 2 and 3 are given in Tables 3, 4, and 5, respectively. The use of the limestones and simulated limestones of different content of magnesium, as sources of calcium, had no statistically significant effect (P < .05) on egg production, feed conversion, or score of shell texture. Nor did there appear to be

857

MAGNESIUM IN LIMESTONE FOR LAYERS TABLE 3.—Averages of the measures of performance of the chickens in Experiment 1 Ratio of Total MgCOs to Mg CaC(V in diet

0:100 9:91 18:82 27:73

P.p.m. 1,640 3,360 5,650 8,380

Egg , - ..

P

roductlon

Percent 38.6 42.4 44.0 39.2

Feed conversionb

2.91 3.00 2.74 2.95

Egg weight

Shell strength

Grams Kilograms 50.5 2.64 52.7 2.55 52.3 2.80 52.4 2.63

Score of shell texture"

3.88 3.91 3.87 3.90

Hatchability of fertile eggs

Gain in live weight

Score of excretad

Percent 71.8 56.8 70.8 70.7

Grams 273 446 447 357

2.42 2.62 2.25 1.91

• See footnoteb, Table 2. b Kilograms of feed consumed per dozen eggs produced. 0 Each hen's eggs were scored 1 (very rough shells), 2 (moderately rough shells), 3 (slightly rough shells), or 4 (normal, smooth shells). d Each hen's excreta were scored 1 (watery-liquid), 2 (very wet-pasty), 3 (normal-formed), or 4 (drywell formed). Significant differences: Egg weight: 0:100<9:91(P<.01), 18:82 and 27:73(P<.02). Shell strength: 18:82>9:91(P<.001), 0:100 and 27:73(P<.05). Hatchability: 9:91<0:100 and 27:73(P<.005), 18:82(P<.002). Gain in live weight: 0:100<9:91 and 18:82(P.<02). Score of excreta: 0:100<9:91(P<.01). 18:82<0:100(P<.05), 9:91(P<.001). 27:73<0:100, 9:91, 18:82(P<.001).

any consistent trends in these measures of performance as a result of the level of magnesium in the calcium supplement. There were significant differences (P < .05) in egg weight, strength of shell, hatchability of fertile eggs, gain in live weight, and score of dryness of excreta seemingly attributable to the level of magnesium in the calcium supplement. These differences, however, with the exception of those pertaining to the dryness of the excreta, were not consistent in the three experiments. In Experiment 1, the eggs were

significantly lighter in weight in the instance in which the ratio of magnesium carbonate to calcium carbonate in the calcium supplement was 0:100 than in the other instances. There were no significant differences in egg weight in the other two experiments. In Experiment 1, significantly greater shell strength occurred at the ratio of 18:82 than at the other ratios, but in Experiment 3 almost the poorest shell strength occurred at this ratio. In Experiment 2, shell strength was significantly less at the ratio of 27:73 than at the ratios of

TABLE 4.—Averages of the measures of performance of the chickens in Experiment 2 Ratio of Total v MgCOs to Mg jgf. CaCCV in diet P r °duction

versionb

P.p.m. 1,770 3,520 5,810 8,370

2.93 2.81 2.87 2.77

1:99 9:91 18:82 27:73

Percent 46.3 47.0 45.4 44.7

Feed con-

Egg weight

Shell strength

Grams Kilograms 53.3 2.72 53.6 2.66 54.7 2.71 53.9 2.51

».b,c.d see footnotes, Table 3. Significant differences: Shell strength: 27:73<1:99(P<.02), 18:82(P<.02)

Score of shell texture 0

Hatchability of fertile eggs

Gain in live weight

Score of excretad

3.92 3.90 3.95 3.92

Percent 76.5 73.8 79.4 78.3

Grams 611 518 641 571

2.77 2.78 2.86 2.75

858

A. L. MEHRING, JR. AND D. JOHNSON, JR. TABLE 5.—Averages of the measures of performance of the chickens in Experiment 3

Ratio of MgC0 3 to CaC03»

Total .Mg in diet

Total P in diet

1:99

P.p.m. 1,842 1,818

Percent Percent 0.35 46.2 0.60 60.5 Av. 53.4

9:91

4,013 4,060

0.35 0.60 Av.

18:82

7,333 7,253

27:73

11,475 11,555

Feed Egg Egg Conproduction versionb weight

Shell weight

HatchaScore bility of Gain Score of shell fertile in live of 0 d texture eggs weight excreta

2.51 2.19 2.35

Grams Kilograms 54.8 3.24 3.95 3.23 3.92 56.1 55.4 3.23 3.94

Percent Grams 87.5 400 89.2 581 88.4 491

46.5 61.9 54.2

2.49 1.98 2.23

55.6 54.9 55.3

3.32 3.30 3.31

3.96 3.95 3.96

89.9 89.7 89.9

465 519 492

2.53 2.78 2.66

0.35 0.60 Av.

55.0 56.8 55.9

2.16 2.20 2.18

55.8 56.5 56.1

3.18 3.22 3.20

3.96 3.97 3.97

88.8 89.8 89.4

512 508 510

2.62 2.76 2.69

0.35 0.60 Av.

55.7 55.6 55.6

2.19 2.13 2.16

56.1 57.4 56.8

3.16 3.22 3.19

3.92 3.91 3.92

86.6 90.8 88.7

524 551 538

2.47 2.48 2.47

2.60 2.72 2.67

a,b,c,d g e e footnotes, 'rable 3. Significant differences: Egg production: 0.6% P > 0 . 3 5 % P( (P<.001). Interaction: Ratio of MgC0 3 to CaC0 3 XLevel of P (P-C05). Feed conversion: 0.6% P < 0 . 3 5 % P (P<.002). Interaction: Ratio of MgC0 3 to CaC0 3 XLevel of P (P<.05). Score of excreta: 27:73<1:99 and 18:82 (P<.001), 9:91 (P<.005). 0.35% P < 0 . 6 % P(P<.001).

9:91 and 18:82. In Experiment 3, shell strength was less at the ratio of 27:73 than at the ratios of 1:99 and 9:91, though not significantly less; but in Experiment 1, at the ratio of 27:73, shell strength was as good as or better than at the ratios of 0:100 and 9:91. There was a significant difference in hatchability in only one of the three experiments. Hatchability was significantly less at the ratio of 9:91 than at the other ratios, in Experiment 1. There was no apparent trend in hatchability as a result of treatment. Differences in gain in live weight were significant only in Experiment 1. The chickens on the treatments in which the ratios were 0:100 and 27:73 gained less than those on the treatments in which the ratios had intermediate values, and the gain by those at the smaller ratio was significantly less (P < .02). The diet used in this treatment (ratio of 0:100) contained a high level of U.S.P. calcium car-

bonate which made the feed unusually dusty, and we believe less palatable. Consumption of this diet was appreciably less than that of the other diets, and the smaller gain in live weight we believe was due to the smaller quantity of feed consumed. The pattern of gains in live weight observed in Experiment 1 was not repeated in the other experiments. Because of the inconsistencies in the results of the three experiments, it is doubtful that the ratio of magnesium carbonate to calcium carbonate in the limestones and simulated limestones had any effect on egg weight, strength of shell, hatchability, or gain in live weight. There were significant differences (P < .05) in the score of dryness of excreta. The excreta of the chickens were significantly wetter (P < .005) at the ratio of 27:73 than at the other ratios in Experiments 1 and 3. They were slightly wetter at this ratio, but not significantly

MAGNESIUM IN LIMESTONE FOR LAYERS

so, in Experiment 2. These observations agree well with those of Supplee (1963). He noted slightly more moisture in the excreta of laying chickens fed diets in which the ratio of magnesium carbonate to calcium carbonate in the combined supplement of U.S.P. magnesium carbonate and U.S.P. calcium carbonate was 27:73, than at smaller ratios. Moreover, he noted no other effect on the chickens as a result of this combination of supplementary magnesium and calcium (total dietary magnesium was 9,000 p.p.m.). In another paper, Mehring (1965) reported on the effects of limestones of varying content of magnesium as sources of calcium in the diet of chicks to eight weeks of age, and he noted that slightly wetter excreta were produced by the chicks that were fed the diet containing the highest level of magnesium of 6,805 p.p.m. (5,000 p.p.m. added by way of the simulated limestone) than were produced by the chicks fed the diets containing lower levels of magnesium. In these experiments with laying chickens, similar levels of magnesium, ranging from 5,650 to 7,333 p.p.m. (ratio of 18:82), did not appear to produce excreta wetter than normal. This difference in response between chicks and layers suggests that older chickens may be more tolerant of the higher levels of magnesium. It had been noted in a number of previous experiments at this laboratory that pullets come into production rapidly and reach a peak of lay during the third month when kept under the environmental conditions outlined in this paper. Quite abruptly after the third month, production begins declining and continues in a straight-line decent right up to the end of the laying year. We thought that a gradual increase in the period of illumination, simulating the increasing length of daylight that occurs naturally in the winter and spring in

859

this hemisphere, might decrease the rate of decline in egg production. No such effect was noted, however; and, as a result, the same constant lighting schedule used in the earlier experiments and in Experiment 1 reported here was followed in Experiment 3. The results of previous work at this laboratory led us to believe that 0.4 percent of total phosphorus is adequate in the diet of laying chickens under our experimental conditions. In Experiment 3, a somewhat lower level of phosphorus (0.35 percent) was included in the diets of half of the chickens to see if somewhat less than 0.4 percent of phosphorus would be as satisfactory as a level we were confident is entirely adequate (0.6 percent). The results indicated that 0.35 percent of phosphorus was not adequate. The egg production of the chickens fed the diets containing 0.6 percent of phosphorus at the dietary ratios of magnesium carbonate to calcium carbonate of 1:99 and 9:91 was significantly better (P < .001) than that of the chickens fed the diets containing 0.35 percent of phosphorus. Feed conversion was likewise significantly better (P < .002). At the ratios of 18:82 and 27:73, however, the two levels of phosphorus supported equally good egg production and feed conversion. A variance analysis indicated that the interaction between level of phosphorus and ratio of magnesium carbonate equivalent to calcium carbonate equivalent in the added limestones and simulated limestones was significant (P < .05). The results of the three experiments reported here suggest that limestones, in which the ratios of magnesium carbonate to calcium carbonate are as small as 18:82, can be added in sufficient quantity to the diet of laying chickens to raise the level of calcium to 3.0 or 4.0 percent without producing any ill effects. In these experiments, such limestones resulted in total dietary levels of magnesium of 5,650 to 7,293

860

A. L. MEHRING, JR. AND D. JOHNSON, JR.

p.p.m. Limestones in which the ratios of magnesium carbonate to calcium carbonate are as large as 27:73 might be expected to increase the moisture content of the excreta. In Experiments 1 and 2, limestone having this ratio produced a dietary level of 8,370 p.p.m. of magnesium, but in Experiment 3, in which the level of calcium was higher, it produced a dietary level of 11,515 p.p.m.

dietary p.p.m., than at nesium

magnesium was 8,370 to 11,515 the excreta were slightly wetter the other ratios (total dietary magof 7,293 p.p.m. or less). ACKNOWLEDGMENT

The high-calcium limestone used in these experiments was supplied through the courtesy of Calcium Carbonate Company, Quincy, Illinois.

SUMMARY

Three 48-week experiments were conducted with laying chickens in batteries of individual cages kept in an environmentcontrolled room. U.S.P. calcium carbonate, U.S.P. magnesium oxide, calcite flour, a high-calcium limestone, and a high-magnesium limestone were combined in various proportions to simulate limestones of different content of magnesium and calcium as expressed by the ratio of magnesium carbonate equivalent to calcium carbonate equivalent. The ratios were 0:100, 9:91, 18:82, and 27:73. Enough of the simulated limestones were added to a cornsoybean meal diet to provide 3.0 percent of calcium in the diets of two of the experiments, and the total phosphorus content of the diets was adjusted at 0.4 percent. In the third experiment, the level of calcium was increased to 4.0 percent, and the phosphorus content was adjusted at 0.35 percent in the diets of half the chickens and at 0.6 percent in the diets of the other half. The ratio of magnesium carbonate to calcium carbonate did not appear to influence egg production, feed conversion, egg weight, shell strength, shell texture, hatchability, or gain in live weight. The level of 0.35 percent of dietary phosphorus resulted in poorer egg production and feed conversion than the level of 0.6 percent at the two smaller ratios (0:100 and 9:91), but not at the two larger ratios (18:82 and 27:73). The interaction was significant. At the largest ratio (27:73), in which total

REFERENCES Alder, B., 1927. The use of calcite and other natural deposits of calcium carbonate in the ration of laying hens. Proc. 3rd World's Poultry Congress: 231-234. Buckner, G. D., J. H. Martin and W. M. Insko, Jr., 1932. The effect of MgCQ, when added to diets of growing chicks. Poultry Sci. 1 1 : 58-62. Branion, H. D., 1947. Minerals in animal and poultry nutrition. Proc. 7th Annual Meeting of the Nutrition Council of the A.F.M.A.: 7-10. Halloran, H. R., J. B. Lyle and H. S. Nakaue, 1961. Magnesium for laying pullets. Feedstuffs, July IS: 40-41. Mehring, A. L., Jr., 1949. A device for measuring the strength of shells of eggs. Poultry Sci. 28: 621-622. Mehring, A. L., Jr., 1965. The effect of magnesium in limestone on the growth and tibia ash of chicks. Poultry Sci. 44: 345-349. Staller, B. L., and M. L. Sunde, 1964. Magnesium carbonate and dolomitic limestone in practical laying rations. Poultry Sci. 43 : 1365. Supplee, W. C , 1963. Observations on the effect of several minerals in poultry feed. Proc. Maryland Nutr. Conf. for Feed Mfg.: 98-101. Titus, H. W., 1961. The Scientific Feeding of Chickens (4th Ed.), The Interstate, Danville, 111.: 253-257. Tully, W. C , and K. W. Franke, 1934. Comparative metabolism of several calcareous materials used in poultry feeding. South Dakota Exp. Sta. Bull. 287. Walker, R. H., 1949. Magnesium carbonate instead of calcium carbonate decreases egg production. Utah Agric. Exp. Sta. Biennial Report. 19461948: 11. Wheeler, W. P., 1919. Some studies relating to calcium metabolism. New York Agric. Exp. Sta. Bull. 468.