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Limestone Buffers in Complete Mixed Rations for Dairy Cattle1
L i m e s t o n e B u f f e r s in C o m p l e t e M i x e d R a t i o n s f o r D a i r y C a t t l e ~ W. E. WHEELER 2 and C. H. NOLLER Department of Animal Sciences Purdue University Lafayette, IN
of starch was approximately 10 percentage units lower. These depressions in digestibility of dietary starch accounted for 34.2 to 50.2% of the total reduction in availability of dietary energy (14) at feed intakes above maintenance for dairy cattle fed high energy rations. Wheeler et al. (16) reported that steers fed all-concentrate rations had considerable quantities o f starch in feces with intestinal pH values well below neutrality. In contrast, Kern et al. (6) found that steers fed an all t i m o t h y hay diet had intestinal pH values between 7.0 and 7.3. These observations suggest that decreased starch digestion at high feed intakes may be related, in part, to reduced activity o f pancreatic alpha amylase in the small intestine due to pH values below the optimal 6.9 (8). If intestinal pH for cattle fed high energy rations is below 6.9, the addition of buffers capable of increasing intestinal pH should reduce the loss of starch in feces and improve feed efficiency. Our purpose was to determine the influence of adding limestone buffers to high energy rations on fecal pH, loss of dietary starch in feces, weight gain, milk yield, and feed efficiency of dairy cattle.
ABSTRACT
In two feeding trials lactating dairy cows were fed limestone and in one trial growing dairy heifers were fed magnesium-limestone-buffered rations. Complete mixed rations based on corn silage and corn grain were fed ad libitum. In Trial 1, cows fed a ration with 2.76% limestone consumed 7.36% less dry matter of feed than cows fed a ration containing. 11% added limestone, with no effect on milk production. In Trial II, cows fed a ration with 2.71% limestone had similar feed intakes and milk production but gained more weight than cows fed a ration with .01% limestone. Heifers fed a ration supplemented with magnesium limestone gained .49 kg more weight per day and made more efficient use of feed than heifers fed the nonsupplemented ration. Limestone increased fecal pH from 5.99 to 6.62 in Trial 1, 6.13 to 6.57 in Trial II and decreased loss of starch in feces. Magnesium limestone increased fecal pH from 6.37 to 6.76 and decreased starch in feces from 5.60 to 1.14%. In these trials both limestone and magnesium limestone increased fecal pH, reduced starch losses in the feces, and improved feed efficiency.
EXPERIMENTAL PROCEDURE Trial I
INTRODUCTION
Digestion trials with dairy cows at feed intakes for maintenance indicate almost complete utilization of dietary starch (14). During lactation when feed intakes ranged from 2.5 to 3.2 multiples of maintenance, the digestibility
Received March 11, 1976. l Journal Paper No. 6227, Purdue University Agricultural Experiment Station. 2 USDA, ARS, Nutrition Institute, Ruminant Nutrition Laboratory, Beltsville, MD 20705. 3Ru-min-aid, Quali-Tech Products, Inc., 318 Lake l-Iazdtine Drive, Chaska, Minnesota 55318.
Fifty-four lactating Holstein cows were assigned to trios on age at calving, stage of lactation, and milk production. Cows within trios were assigned at random to one of three groups, and the groups were allotted randomly to treatment sequences for a Latin square design with 14-day experimental periods. The cows were group-fed complete mixed rations which on a dry basis contained a 60:40 ratio of forage to concentrate. Corn silage was the only forage. Concentrate mixtures (Table 1) were calculated so that the total ration would provide 15% crude protein, .5% phosphorus, and .5% trace mineralized salt on a dry matter basis. Ground limestone was added to the
1788
TABLE 1. Ingredient composition of concentrates and s u p p l e m e n t s fed in trials I, II, and III.a Rations, Trial I Ingredient
1
2
Rations, Trial III
Rations, Trial II 3
4
5
6 and 7 ~q
(%) Shelled corn (rolled-medium) Soybean meal (49% CP) Urea Dicalcium phosphate Limestone Trace mineral salt b Elemental sulfur Magnesium oxide Vitamin premix
68•34 26.13 1.12 2•40 .27 1.17 .13 .05 .39 e 100•00
64•04 27.07 1.12 2•46 3.56 1.17 .13 .06 .39 c 100.00
59•71 28.01 1.13 2•51 6.89 1 •17 .13 .06 .39 c 100.00
aDry-matter basis. bGuaranteed to contain n o t less t h a n .50% Zn, .40% Mn, •25% Fe, .05% Cu, .01% 12, and •01% Co.
9 i :31
79:84
91:42
"4185 .08 2•65 .11 . . 1.00 c
"4:23 12.73 2•25 .10 . . .85 c
"5135 .09 2•92 .12
100•00
.
.
100.00
.
Z ¢¢
. .10 d 100.00
O Z
CSupplied 2200 IU vitamin A and 1000 IU vitamin D per kilogram o f ration dry matter. d s u p p l i e d 1670 IU vitamin A and 300 IU vitamin D per kilogram of ration dry matter. o] o <
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TABLE 2. Ingredient and chemical composition o f complete mixed rations fed in trials I, II, and Ill a.
t~
Rations, Trial I
Z
1
O
Rations, Trial II
2
3
4
Rations, Trial 1II 5
6
7
35.0 10.0 37.2
35.0 10.0 33.7
50.0
48.8
3615
3516
1718 . .
2113 .
1315
1312 2.4
(%) Component Corn silage Alfalfa-grass silage Corn earlage Concentrate Supplement Magnesium limestone b Chemical composition Crude protein Starch Cell wall Calcium Phosphorus
60.0 . . 4010 . . . . 15.3 34.3 32.8 .48 .44
.
.
.
.
. .
. .
60.0 . . 4010 . . . . 15.1 34.0 33.1 .87 .43
aDry-matter basis. bGuaranteed to contain not less than 20% Ca and 10% Mg.
60.0 .
.
r~
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. .
.
.
.
14.8 34.9 32.4 1.41 .45
.
.
15.4 36.7 35.0 .51 .52
.
.
15.6 34.2 34.5 1.48 .51
. 12.4 35.4 32.1 .37 .37
12.1 34.6 31.4 .72 .35
7~
> X Z 0
LIMESTONE BUFFERS IN DAIRY RATIONS concentrate mixtures to provide calcium to phosphorus ratios of 1:1, 2:1, and 3:1 for the respective rations on a dry basis. Ingredient composition of the complete feeds are in Table 2. Cows were housed in a free-stall barn with sawdust as bedding. Complete feeds were blended daily in a horizontal mixer wagon equipped with electronic load cells and fed once daily in amounts sufficient for about 5% feed refusal. Daily records were kept of feed offered and refused. Milk weights were recorded daily with AM and PM samples taken once weekly for milk fat determination (1). Samples of the complete mixed rations were oven-dried at 60 C, equilibrated to air, and ground for laboratory analyses. Dry matter was determined by oven-drying at 100 C, nitrogen by Kjeldahl, calcium by atomic absorption spectrophotometry (17), and phosphorus by procedures of Harris and Popat (5). Starch content of the samples was determined by methods of Wheeler et al. (14). Neutral detergent fiber for the complete feeds was by procedures of Van Soest (11). Fresh fecal samples were collected from six randomly selected trios and pH determined with a general purpose combination pH electrode. Analysis of variance was by procedures of Cochran et al. (3). Differences among treatment means were by Newman-Keuls Sequential Range Test (7). Trial I I
A switchback design was utilized for a feeding trial with 36 lactating Holstein cows paired according to lactation number, stage of lactation, and milk production. Cows within each pair were assigned at random to treatment sequences with 14-day experimental periods. Complete mixed rations (Table 2) contained 45% forage and 55% concentrate, on a dry basis. Dry matter of the forage was 77.8% corn silage and 22.2% alfalfa-bromegrass silage. The concentrate portion of the ration consisted of corn earlage and a supplement (Table 1) formulated to provide complete mixed rations with 15.5% crude protein, .5% phosphorus, and .5% trace mineralized salt in the dry matter. Ground limestone was varied in the supplements to provide a calculated calcium to phosphorus ratio of either 1:1 or 3:1 in the ration dry matter.
1791
Housing, management, feeding, samples, and analyses were as described for Trial I. Fresh fecal material was collected from each cow. An aliquot of fecal material was oven-dried at 60 C, equilibrated to atmospheric conditions, ground, and analyzed for starch. Data were analyzed according to procedures of Brandt (2). Trial I I I
Fourteen Holstein heifer calves, weighing 279 to 467 kg, were paired on age and weight for random assignment to treatment sequences for a switchback design with 14-day experimental periods. Complete mixed rations (Table 2) were fed with about equal parts of dry matter from corn silage and concentrate. The concentrate portion o f the ration was corn earlage and a supplement (Table 1) varied to provide 12% crude protein, . 35 % calcium, . 35 % phosphorus, and .5% trace mineralized salt in the total ration dry matter. Magnesium limestone 3 was used as the buffer to provide about 198 g per animal daily. Ingredient composition and chemical analyses of the complete feeds are in Table 2. Animals were housed in a stanchion barn and fed individually with sawdust as bedding. Heifers were weighed at 14-day intervals prior to the AM feeding. All other procedures were as described for Trials I and II. RESULTS
AND
DISCUSSION
Feed intakes, milk production, body weight change, fecal pH, and fecal starch values for the three trials are in Table 3. A similarity in response to ration by both low and high producing cows in Trial I is indicated by the absence of interactions (P>.25) between limestone in the ration and cow trios for all responses. Average daily intakes o f dry matter by cows in Trial I were 16.3, 16.1, and 15.3 kg for complete mixed rations with either .11, 1.42, or 2.76% added limestone. Cows fed the high limestone ration consumed 7.36% less dry matter (P<.05) than cows in the low limestone group. However, the addition of limestone had no effect (P>.05) on feed intakes in Trials II and IIl (Table 3). Lactating cows in Trials I and II receiving diets with added limestone had a tendency to produce less (P>.05) milk with a slightly higher (P>.05) fat test but with no difference (P>.25) among rations for fat-corJournal of Dairy Science Vol. 59, No. 10
1792
WHEELER AND NOLLER
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rected milk (FCM). Animals fed the high limestone ration in Trial I consumed less feed, but they produced the same amount of FCM with similar weight gains resulting in a more efficient use of feed. In Trial II, feed intakes and FCM production were similar (P>.25) between groups, but animals fed ration 5 with 2.71% limestone gained .66 kg weight daily (P<.01) compared with a loss of .27 kg per day by cows fed ration 4 containing .01% limestone. In Trial III with growing dairy heifers, daily feed intakes were 8.55 and 8.34 kg (P>.05) on the control and magnesium limestone supplemented rations (Table 3). Weight gains were .49 kg per day higher (P<.01) for heifers fed the magnesium limestone supplemented ration. Feed efficiencies were 6.93 and 4.85 kg feed dry matter per kg body weight gain (P<.01) for the two groups. In all three trials, there was an improvement in the efficiency of feed utilization for milk production or weight gain due to the addition of limestone or magnesium limestone buffers. Control rations for these three trials had calcium-to-phosphorus ratios of essentially 1:1 as determined by laboratory analyses of the complete mixed rations. Calcium in these rations was similar to or above National Research Council (10) requirements for dairy cattle. In previous reports, researchers have a t t e m p t e d to explain the improved performance and feed efficiency from the supplementation o f rations with additional limestone to a higher requirement for calcium (13) or to a buffering effect in the rumen which modified metabolism in the rumen (12). The data indicate that the value of additional limestone or magnesium limestone is not dependent only upon an effect in the rumen, but also to a buffering effect in the lower gastrointestinal tract. Studies of pH in the various segments of the gastrointestinal tract of ruminants fed high energy diets (16) have shown that pH values in the small intestine were nearer 6.0 than the 6.9 necessary for optimal activity of pancreatic alpha amylase (8). Fecal pH was used in our study as an indicator of pH in the small intestine because of difficulties in obtaining ingesta from the small intestine of live animals. The rationale for using fecal pH is based on research demonstrating that fecal pH values were not different (P>.IO) from pH values in the small intestine (16).
LIMESTONE BUFFERS IN DAIRY RATIONS Fecal pH values were 5.99, 6.13, and 6.37 for animals fed the low-limestone, or control, rations in the three trials (Table 3). Since these values are considerably below the p H necessary for optimal activity of pancreatic alpha amylase in the small intestine, a greater loss of starch in feces should be expected. The addition of 2.71% limestone in Trial II increased fecal pH f r o m 6.13 to 6.57 (P<.01). The increase in fecal pH was a c c o m p a n i e d by a 4.95 (7.96 to 3.01) percentage unit r e d u c t i o n (P<.01) in loss of starch in feces. There were similar results in Trial III where growing dairy heifers fed ration 6 had a fecal pH o f 6.37 and 5.60% starch in feces. When 198 g magnesium limestone were fed daily per animal, fecal p H increased to 6.76 and starch in feces declined to 1.14%. The relatively l o w fecal starch values for the t w o groups of heifers in Trial 1II may reflect a more efficient use o f starch at lower feed intakes by these heifers as c o m p a r e d with the lactating cows in Trials I and II. There appears to be little a g r e e m e n t a m o n g research workers concerning the influence of buffers on p e r f o r m a n c e of lactating dairy cows. Sodium bicarbonate and potassium bicarbonate buffers have been used to reverse depressions in milk fat p r o d u c t i o n of dairy cows fed highgrain diets w i t h o u t an increase in actual milk p r o d u c t i o n (4, 9). Since s o d i u m and p o t a s s i u m are absorbed readily f r o m the digestive tract c o m p a r e d to calcium and magnesium (10), t h e y are unlikely to have m u c h influence on pH in the small intestine. If the pH in the small intestine is t o o low for optimal activity o f pancreatic alpha amylase, the addition o f buffers capable o f increasing p H in the small intestine should improve starch utilization. This is supported by research in which the addition of either limestone or magnesium limestone to high energy rations had little effect on pH in the reticulo-rumen, but there was a substantial increase (P<.01) of pH in the small intestine and a r e d u c t i o n (P<.01) in loss of starch in feces (15). Addition o f either limestone or magnesium limestone buffer increased ration efficiency by improving the utilization o f starch in the small intestine with a decline in the loss of energy as starch in feces. The effectiveness o f limestone and magnesium limestone in improving ration
1793
efficiency is a t t r i b u t e d to an increase in intestinal pH which provides a m o r e favorable pH for pancreatic alpha amylase activity. REFERENCES
1 Association of Official Agricultural Chemists. 1970. Official methods of analysis, l l t h Ed. Washington, DC. 2 Brandt, A. E. 1938. Tests of significance in reversal or switchback trials. Iowa Agr. Exp. Sta. Res. Bull. 234. 3 Cochran, W. G., K. M. Autrey, and C. Y. Cannon. 1941. A double change-over design for dairy cattle feed experiments. J. Dairy Sci. 24:937. 4 Emery, R. S., and L. D. Brown. 1961. Effect of feeding sodium and potassium bicarbonate on milk fat, tureen pH and volatile fatty acid production. J. Dairy Sei. 44:1899. 5 Harris, W. D., and P. Popat. 1954. Determination of phosphorus content of lipids. Amer. Oil Chemist's Soc. J. 31:124. 6 Kern, D. L., L. L. Slyter, E. C. Leffel, J. M. Weaver, and R. R. Ohjen. 1974. Ponies vs. steers: microbial and chemical characteristics of intestinal ingesta. J. Anim. Sci. 38:559. 7 Keuls, M. 1952. THe use of the "studentized range" in connection with analysis of variance. Euphytica 1:112. 8 Long, C. 1961. Biochemists' Handbook. D. Van Nostrand Co., New York. 9 Miller, R. W., R. W. Hemken, D. R. Waldo, M. Okamoto, and L. A. Moore. 1965. Effect of feeding buffers to dairy cows fed a high-concentrate, low-roughage ration. J. Dairy Sci. 48:1455. 10 National Research Council. 1971. Nutrient requirements of dairy cattle. 4th rev. ed. National Academy of Sciences, Washington, DC. Publication ISBN 0-309-01916-8. 11 Van Soest, P. J. 1967. Development of a comprehensive system of feed analyses and its application to forages. J. Anim. Sci. 26:119. 12 Varner, L. W., and W. Woods. 1972. Effect of calcium and starch additions upon ration digestibility by steers. J. Anita. Sci. 35:410. 13 Varner, L. W., and W. Woods. 1972. Calcium levels in high grain beef cattle rations. J. Anim. Sci. 34:415. 14 Wheeler, W. E., C. H. Noller, and C. E. Coppock. 1975. Effect of forage-to-concentrate ratio in complete feeds and feed intake on digestion of starch by dairy cows. J. Dairy Sci. 58:1902. 15 Wheeler, W. E., and C. H. Noller. 1976. Limestone buffers and ruminant digestive tract pH. J. Anita. Sci. 42:1365. (Abstr.). 16 Wheeler, W. E., C. H. Noller, and R. S. Lowrey. 1976. Ruminant digestive tract pH and loss of starch in feces. J. Anim. Sci. 42:277 (Abstr.). 17 Willis, J. B. 1963. Analysis of biological materials by atomic absorption spectroscopy. Page 1 in Methods of biological analysis, vol. XI. lnterscience Publishers, New York.
Journal of Dairy Science Vol. 59, No. 10
of starch was approximately 10 percentage units lower. These depressions in digestibility of dietary starch accounted for 34.2 to 50.2% of the total reduction in availability of dietary energy (14) at feed intakes above maintenance for dairy cattle fed high energy rations. Wheeler et al. (16) reported that steers fed all-concentrate rations had considerable quantities o f starch in feces with intestinal pH values well below neutrality. In contrast, Kern et al. (6) found that steers fed an all t i m o t h y hay diet had intestinal pH values between 7.0 and 7.3. These observations suggest that decreased starch digestion at high feed intakes may be related, in part, to reduced activity o f pancreatic alpha amylase in the small intestine due to pH values below the optimal 6.9 (8). If intestinal pH for cattle fed high energy rations is below 6.9, the addition of buffers capable of increasing intestinal pH should reduce the loss of starch in feces and improve feed efficiency. Our purpose was to determine the influence of adding limestone buffers to high energy rations on fecal pH, loss of dietary starch in feces, weight gain, milk yield, and feed efficiency of dairy cattle.
ABSTRACT
In two feeding trials lactating dairy cows were fed limestone and in one trial growing dairy heifers were fed magnesium-limestone-buffered rations. Complete mixed rations based on corn silage and corn grain were fed ad libitum. In Trial 1, cows fed a ration with 2.76% limestone consumed 7.36% less dry matter of feed than cows fed a ration containing. 11% added limestone, with no effect on milk production. In Trial II, cows fed a ration with 2.71% limestone had similar feed intakes and milk production but gained more weight than cows fed a ration with .01% limestone. Heifers fed a ration supplemented with magnesium limestone gained .49 kg more weight per day and made more efficient use of feed than heifers fed the nonsupplemented ration. Limestone increased fecal pH from 5.99 to 6.62 in Trial 1, 6.13 to 6.57 in Trial II and decreased loss of starch in feces. Magnesium limestone increased fecal pH from 6.37 to 6.76 and decreased starch in feces from 5.60 to 1.14%. In these trials both limestone and magnesium limestone increased fecal pH, reduced starch losses in the feces, and improved feed efficiency.
EXPERIMENTAL PROCEDURE Trial I
INTRODUCTION
Digestion trials with dairy cows at feed intakes for maintenance indicate almost complete utilization of dietary starch (14). During lactation when feed intakes ranged from 2.5 to 3.2 multiples of maintenance, the digestibility
Received March 11, 1976. l Journal Paper No. 6227, Purdue University Agricultural Experiment Station. 2 USDA, ARS, Nutrition Institute, Ruminant Nutrition Laboratory, Beltsville, MD 20705. 3Ru-min-aid, Quali-Tech Products, Inc., 318 Lake l-Iazdtine Drive, Chaska, Minnesota 55318.
Fifty-four lactating Holstein cows were assigned to trios on age at calving, stage of lactation, and milk production. Cows within trios were assigned at random to one of three groups, and the groups were allotted randomly to treatment sequences for a Latin square design with 14-day experimental periods. The cows were group-fed complete mixed rations which on a dry basis contained a 60:40 ratio of forage to concentrate. Corn silage was the only forage. Concentrate mixtures (Table 1) were calculated so that the total ration would provide 15% crude protein, .5% phosphorus, and .5% trace mineralized salt on a dry matter basis. Ground limestone was added to the
1788
TABLE 1. Ingredient composition of concentrates and s u p p l e m e n t s fed in trials I, II, and III.a Rations, Trial I Ingredient
1
2
Rations, Trial III
Rations, Trial II 3
4
5
6 and 7 ~q
(%) Shelled corn (rolled-medium) Soybean meal (49% CP) Urea Dicalcium phosphate Limestone Trace mineral salt b Elemental sulfur Magnesium oxide Vitamin premix
68•34 26.13 1.12 2•40 .27 1.17 .13 .05 .39 e 100•00
64•04 27.07 1.12 2•46 3.56 1.17 .13 .06 .39 c 100.00
59•71 28.01 1.13 2•51 6.89 1 •17 .13 .06 .39 c 100.00
aDry-matter basis. bGuaranteed to contain n o t less t h a n .50% Zn, .40% Mn, •25% Fe, .05% Cu, .01% 12, and •01% Co.
9 i :31
79:84
91:42
"4185 .08 2•65 .11 . . 1.00 c
"4:23 12.73 2•25 .10 . . .85 c
"5135 .09 2•92 .12
100•00
.
.
100.00
.
Z ¢¢
. .10 d 100.00
O Z
CSupplied 2200 IU vitamin A and 1000 IU vitamin D per kilogram o f ration dry matter. d s u p p l i e d 1670 IU vitamin A and 300 IU vitamin D per kilogram of ration dry matter. o] o <
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TABLE 2. Ingredient and chemical composition o f complete mixed rations fed in trials I, II, and Ill a.
t~
Rations, Trial I
Z
1
O
Rations, Trial II
2
3
4
Rations, Trial 1II 5
6
7
35.0 10.0 37.2
35.0 10.0 33.7
50.0
48.8
3615
3516
1718 . .
2113 .
1315
1312 2.4
(%) Component Corn silage Alfalfa-grass silage Corn earlage Concentrate Supplement Magnesium limestone b Chemical composition Crude protein Starch Cell wall Calcium Phosphorus
60.0 . . 4010 . . . . 15.3 34.3 32.8 .48 .44
.
.
.
.
. .
. .
60.0 . . 4010 . . . . 15.1 34.0 33.1 .87 .43
aDry-matter basis. bGuaranteed to contain not less than 20% Ca and 10% Mg.
60.0 .
.
r~
4010 .
. .
.
.
.
14.8 34.9 32.4 1.41 .45
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.
15.4 36.7 35.0 .51 .52
.
.
15.6 34.2 34.5 1.48 .51
. 12.4 35.4 32.1 .37 .37
12.1 34.6 31.4 .72 .35
7~
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LIMESTONE BUFFERS IN DAIRY RATIONS concentrate mixtures to provide calcium to phosphorus ratios of 1:1, 2:1, and 3:1 for the respective rations on a dry basis. Ingredient composition of the complete feeds are in Table 2. Cows were housed in a free-stall barn with sawdust as bedding. Complete feeds were blended daily in a horizontal mixer wagon equipped with electronic load cells and fed once daily in amounts sufficient for about 5% feed refusal. Daily records were kept of feed offered and refused. Milk weights were recorded daily with AM and PM samples taken once weekly for milk fat determination (1). Samples of the complete mixed rations were oven-dried at 60 C, equilibrated to air, and ground for laboratory analyses. Dry matter was determined by oven-drying at 100 C, nitrogen by Kjeldahl, calcium by atomic absorption spectrophotometry (17), and phosphorus by procedures of Harris and Popat (5). Starch content of the samples was determined by methods of Wheeler et al. (14). Neutral detergent fiber for the complete feeds was by procedures of Van Soest (11). Fresh fecal samples were collected from six randomly selected trios and pH determined with a general purpose combination pH electrode. Analysis of variance was by procedures of Cochran et al. (3). Differences among treatment means were by Newman-Keuls Sequential Range Test (7). Trial I I
A switchback design was utilized for a feeding trial with 36 lactating Holstein cows paired according to lactation number, stage of lactation, and milk production. Cows within each pair were assigned at random to treatment sequences with 14-day experimental periods. Complete mixed rations (Table 2) contained 45% forage and 55% concentrate, on a dry basis. Dry matter of the forage was 77.8% corn silage and 22.2% alfalfa-bromegrass silage. The concentrate portion of the ration consisted of corn earlage and a supplement (Table 1) formulated to provide complete mixed rations with 15.5% crude protein, .5% phosphorus, and .5% trace mineralized salt in the dry matter. Ground limestone was varied in the supplements to provide a calculated calcium to phosphorus ratio of either 1:1 or 3:1 in the ration dry matter.
1791
Housing, management, feeding, samples, and analyses were as described for Trial I. Fresh fecal material was collected from each cow. An aliquot of fecal material was oven-dried at 60 C, equilibrated to atmospheric conditions, ground, and analyzed for starch. Data were analyzed according to procedures of Brandt (2). Trial I I I
Fourteen Holstein heifer calves, weighing 279 to 467 kg, were paired on age and weight for random assignment to treatment sequences for a switchback design with 14-day experimental periods. Complete mixed rations (Table 2) were fed with about equal parts of dry matter from corn silage and concentrate. The concentrate portion o f the ration was corn earlage and a supplement (Table 1) varied to provide 12% crude protein, . 35 % calcium, . 35 % phosphorus, and .5% trace mineralized salt in the total ration dry matter. Magnesium limestone 3 was used as the buffer to provide about 198 g per animal daily. Ingredient composition and chemical analyses of the complete feeds are in Table 2. Animals were housed in a stanchion barn and fed individually with sawdust as bedding. Heifers were weighed at 14-day intervals prior to the AM feeding. All other procedures were as described for Trials I and II. RESULTS
AND
DISCUSSION
Feed intakes, milk production, body weight change, fecal pH, and fecal starch values for the three trials are in Table 3. A similarity in response to ration by both low and high producing cows in Trial I is indicated by the absence of interactions (P>.25) between limestone in the ration and cow trios for all responses. Average daily intakes o f dry matter by cows in Trial I were 16.3, 16.1, and 15.3 kg for complete mixed rations with either .11, 1.42, or 2.76% added limestone. Cows fed the high limestone ration consumed 7.36% less dry matter (P<.05) than cows in the low limestone group. However, the addition of limestone had no effect (P>.05) on feed intakes in Trials II and IIl (Table 3). Lactating cows in Trials I and II receiving diets with added limestone had a tendency to produce less (P>.05) milk with a slightly higher (P>.05) fat test but with no difference (P>.25) among rations for fat-corJournal of Dairy Science Vol. 59, No. 10
1792
WHEELER AND NOLLER
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10
G
rected milk (FCM). Animals fed the high limestone ration in Trial I consumed less feed, but they produced the same amount of FCM with similar weight gains resulting in a more efficient use of feed. In Trial II, feed intakes and FCM production were similar (P>.25) between groups, but animals fed ration 5 with 2.71% limestone gained .66 kg weight daily (P<.01) compared with a loss of .27 kg per day by cows fed ration 4 containing .01% limestone. In Trial III with growing dairy heifers, daily feed intakes were 8.55 and 8.34 kg (P>.05) on the control and magnesium limestone supplemented rations (Table 3). Weight gains were .49 kg per day higher (P<.01) for heifers fed the magnesium limestone supplemented ration. Feed efficiencies were 6.93 and 4.85 kg feed dry matter per kg body weight gain (P<.01) for the two groups. In all three trials, there was an improvement in the efficiency of feed utilization for milk production or weight gain due to the addition of limestone or magnesium limestone buffers. Control rations for these three trials had calcium-to-phosphorus ratios of essentially 1:1 as determined by laboratory analyses of the complete mixed rations. Calcium in these rations was similar to or above National Research Council (10) requirements for dairy cattle. In previous reports, researchers have a t t e m p t e d to explain the improved performance and feed efficiency from the supplementation o f rations with additional limestone to a higher requirement for calcium (13) or to a buffering effect in the rumen which modified metabolism in the rumen (12). The data indicate that the value of additional limestone or magnesium limestone is not dependent only upon an effect in the rumen, but also to a buffering effect in the lower gastrointestinal tract. Studies of pH in the various segments of the gastrointestinal tract of ruminants fed high energy diets (16) have shown that pH values in the small intestine were nearer 6.0 than the 6.9 necessary for optimal activity of pancreatic alpha amylase (8). Fecal pH was used in our study as an indicator of pH in the small intestine because of difficulties in obtaining ingesta from the small intestine of live animals. The rationale for using fecal pH is based on research demonstrating that fecal pH values were not different (P>.IO) from pH values in the small intestine (16).
LIMESTONE BUFFERS IN DAIRY RATIONS Fecal pH values were 5.99, 6.13, and 6.37 for animals fed the low-limestone, or control, rations in the three trials (Table 3). Since these values are considerably below the p H necessary for optimal activity of pancreatic alpha amylase in the small intestine, a greater loss of starch in feces should be expected. The addition of 2.71% limestone in Trial II increased fecal pH f r o m 6.13 to 6.57 (P<.01). The increase in fecal pH was a c c o m p a n i e d by a 4.95 (7.96 to 3.01) percentage unit r e d u c t i o n (P<.01) in loss of starch in feces. There were similar results in Trial III where growing dairy heifers fed ration 6 had a fecal pH o f 6.37 and 5.60% starch in feces. When 198 g magnesium limestone were fed daily per animal, fecal p H increased to 6.76 and starch in feces declined to 1.14%. The relatively l o w fecal starch values for the t w o groups of heifers in Trial 1II may reflect a more efficient use o f starch at lower feed intakes by these heifers as c o m p a r e d with the lactating cows in Trials I and II. There appears to be little a g r e e m e n t a m o n g research workers concerning the influence of buffers on p e r f o r m a n c e of lactating dairy cows. Sodium bicarbonate and potassium bicarbonate buffers have been used to reverse depressions in milk fat p r o d u c t i o n of dairy cows fed highgrain diets w i t h o u t an increase in actual milk p r o d u c t i o n (4, 9). Since s o d i u m and p o t a s s i u m are absorbed readily f r o m the digestive tract c o m p a r e d to calcium and magnesium (10), t h e y are unlikely to have m u c h influence on pH in the small intestine. If the pH in the small intestine is t o o low for optimal activity o f pancreatic alpha amylase, the addition o f buffers capable o f increasing p H in the small intestine should improve starch utilization. This is supported by research in which the addition of either limestone or magnesium limestone to high energy rations had little effect on pH in the reticulo-rumen, but there was a substantial increase (P<.01) of pH in the small intestine and a r e d u c t i o n (P<.01) in loss of starch in feces (15). Addition o f either limestone or magnesium limestone buffer increased ration efficiency by improving the utilization o f starch in the small intestine with a decline in the loss of energy as starch in feces. The effectiveness o f limestone and magnesium limestone in improving ration
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efficiency is a t t r i b u t e d to an increase in intestinal pH which provides a m o r e favorable pH for pancreatic alpha amylase activity. REFERENCES
1 Association of Official Agricultural Chemists. 1970. Official methods of analysis, l l t h Ed. Washington, DC. 2 Brandt, A. E. 1938. Tests of significance in reversal or switchback trials. Iowa Agr. Exp. Sta. Res. Bull. 234. 3 Cochran, W. G., K. M. Autrey, and C. Y. Cannon. 1941. A double change-over design for dairy cattle feed experiments. J. Dairy Sci. 24:937. 4 Emery, R. S., and L. D. Brown. 1961. Effect of feeding sodium and potassium bicarbonate on milk fat, tureen pH and volatile fatty acid production. J. Dairy Sei. 44:1899. 5 Harris, W. D., and P. Popat. 1954. Determination of phosphorus content of lipids. Amer. Oil Chemist's Soc. J. 31:124. 6 Kern, D. L., L. L. Slyter, E. C. Leffel, J. M. Weaver, and R. R. Ohjen. 1974. Ponies vs. steers: microbial and chemical characteristics of intestinal ingesta. J. Anim. Sci. 38:559. 7 Keuls, M. 1952. THe use of the "studentized range" in connection with analysis of variance. Euphytica 1:112. 8 Long, C. 1961. Biochemists' Handbook. D. Van Nostrand Co., New York. 9 Miller, R. W., R. W. Hemken, D. R. Waldo, M. Okamoto, and L. A. Moore. 1965. Effect of feeding buffers to dairy cows fed a high-concentrate, low-roughage ration. J. Dairy Sci. 48:1455. 10 National Research Council. 1971. Nutrient requirements of dairy cattle. 4th rev. ed. National Academy of Sciences, Washington, DC. Publication ISBN 0-309-01916-8. 11 Van Soest, P. J. 1967. Development of a comprehensive system of feed analyses and its application to forages. J. Anim. Sci. 26:119. 12 Varner, L. W., and W. Woods. 1972. Effect of calcium and starch additions upon ration digestibility by steers. J. Anita. Sci. 35:410. 13 Varner, L. W., and W. Woods. 1972. Calcium levels in high grain beef cattle rations. J. Anim. Sci. 34:415. 14 Wheeler, W. E., C. H. Noller, and C. E. Coppock. 1975. Effect of forage-to-concentrate ratio in complete feeds and feed intake on digestion of starch by dairy cows. J. Dairy Sci. 58:1902. 15 Wheeler, W. E., and C. H. Noller. 1976. Limestone buffers and ruminant digestive tract pH. J. Anita. Sci. 42:1365. (Abstr.). 16 Wheeler, W. E., C. H. Noller, and R. S. Lowrey. 1976. Ruminant digestive tract pH and loss of starch in feces. J. Anim. Sci. 42:277 (Abstr.). 17 Willis, J. B. 1963. Analysis of biological materials by atomic absorption spectroscopy. Page 1 in Methods of biological analysis, vol. XI. lnterscience Publishers, New York.
Journal of Dairy Science Vol. 59, No. 10