Influence of Dietary Sodium Bicarbonate on the Potassium Metabolism of Growing Dairy Calves1 ,2 W. B. TUCKER,3.4 J. A. JACKSON,4 D. M. HOPKINS,s and J. F. HOGUE3 Department of Animal ScIence University of Kentucky lexington 40546 and Animal Science Department Oklahoma State University Stillwater 74078 ABSTRACT
plemented with NaHC03, and 3) average daily gain and plasma K are sensitive indicators of dietary K in the growing calf. (Key words: potassium, sodium, dairy calf growth, feed intake)
We evaluated the influence of supplemental dietary NaHC03 on K metabolism of young dairy calves. Thirty-two Holstein and Jersey male and female calves were blocked at 56 to 70 dafter birth according to breed, sex, and age and assigned randomly to a 2 x 2 factorial arrangement of dietary treatments for 8 wk: .4% K with 0% NaHC03, .4% K with 2% NaHC03, .6% K with 0% NaHC03, and .6% K with 2% NaHC03. Feed intake was not affected by dietary KCI or NaHC03 supplementation, but average daily gain increased with increased K and tended to be reduced by dietary NaHC03. Plasma K was elevated by increased dietary K but generally was unaffected by NaHC03. Urinary Ca excretion appeared to be reduced by NaHC03; urine pH increased with supplemental NaHC03' Results indicate 1) the K requirement of the growing calf is between .40 and .55% of diet DM, 2) because urinary K excretion was elevated by dietary NaHC03, the K requirement may be increased when the diet is sup-
Abbreviation key: ADG = average daily gain. INTRODUCTION
Received July 23, 1990. Accepted December 6. 1990. IThis manuscript (90-5-128) is published wilh !he approval of the director of the Kentucky Agricultural Ex~riment Station. 2Joumal Article 5792 of the Oklahoma State Agricul~ E~rime~lt Station, StiUwaler 74078. Animal SCIence Department, 01daboma Stale University. Stillwater 74078. '70 whom requests for reprints should be addressed. SDepartment of Anima1 Science, University of Kentucky, Lexington 40546. 1991 J Dairy Sci 74:2296-2302
Historically, ruminants consumed diets high in K-rich forages and, as a result, should have encountered few problems with K deficiencies. In recent years, however, the trend to supplement the diets of dairy animals with proportionately more grain has established K as a potentially limiting nutrient. By-products of the distillery and brewery industries contain less K than forages; when constituting a major porti~n of the diet, they can reduce markedly the dietary K concentration. Well et al. (23) evaluated the K requirement of growing dairy calves and reported that it was between .34 to .58% of diet DM This range is slightly below the .65 to .8% requirement listed for beef cattle (1~) and the .9 to 1% needed for lactating dairy cattle (14) but is similar to the requirement of lambs (.3 to .5%) (2) and higher than concentrations required by chicks (.23 to .40%) (1), young pigs (.26%) (9), and rats (.18%) (7). Although a dietary range has been established for the K requirement of growing dairy calves, the impact of other dietary constituents on this requirement remains to be identified. The ability of dietary buffers to replace the ~eficit in rumen buffering capacity caused by madequate saliva production in young calves has been investigated (8). In Australia, increased growth rate and feed intake were re-
2296
SODWM BICARBONATE EFFECTS ON POTASSIUM
ported with the addition of both 2 and 4% NaHCD 3 to pelleted diets (10); these results were confmned by Kellaway et al. (11) with diets containing either a mixture of 2% NaHCD 3 and 2% NaHP04 , or 4% NaHCD3. More recently, Hart and Polan (8) reported that average daily gain (ADG) was maximized with diets containing between 1 and 2% NaHCD3; higher amounts of buffer tended to reduce performance. Because dietary Na increases with NaHC03 addition, the effects of Na on K metabolism in growing dairy calves need to be evaluated. In nonruminants, high dietary Na intake increases renal K excretion by increasing the flow rate in the late distal tubules and cortical collecting ducts of renal nephrons, thus creating a larger gradient for the diffusion of K into the tubular lumen (22). This response also has been observed in lactating dairy cattle by Rogers et al. (15), who reported an increase (P = .11) in fractional excretion of K when NaHCD3 was fed at 1.2% of diet OM. The objective of this trial was to evaluate the effects of dietary NaHCD 3 on K metabolism in growing dairy calves.
2297
laboratory. Urine, collected via stimulation of the vulva for females and sheath for males at wk 0, 2, 4, 6, and 8, was analyzed for creatinine and then acidified with 3% concentrated HCl. Blood was collected at 0900 h at 0 d and every 14 d thereafter via jugular venipuncture into heparinized, evacuated glass tubes, and centrifuged. Plasma was harvested into clean, polypropylene tubes and frozen for subsequent mineral analyses. Blood plasma and urine Na, K. Ca, and Mg were analyzed via atomic absorption spectrophotometry (Model 4000, Perkin-Elmer Corp., Model 4000, Norwalk, CT) and Cl was analyzed via potentiometric titration (Haake-Buchler Instruments, Inc., Saddlebrook, NJ). Oata were analyzed according to the general linear models procedure of SAS (16); the model included variation due to blocks, dietary K, NaHCD3. the K x NaHCD3 interaction, and residual error. Treatment means and interactions were compared using orthogonal contrasts. Week 0 observations were utilized as covariates for BW and plasma minerals. Significance was declared at P < .10 unless otherwise noted. RESULTS AND DISCUSSION
MATERIALS AND METHODS
Twenty-four Holstein (8 male, 16 female) and 8 Jersey female calves were weaned at 6 wk of age and offered a calf starter concentrate. After intake of the starter reached .9 kg/d (56 to 70 d of age), calves were blocked according to breed, sex, and age and assigned randomly to a 2 x 2 factorial arrangement of dietary treatments: .4% K with 0% NaHCD3, .4% K with 2% NaHCD 3, .6% K with 0% NaHCD3' and .6% K with 2% NaHCD3. After completion of the study, treatment groups were analyzed and found to contain .35, .42, .61, and .53% K, respectively (OM basis). After an initial l-wk adaptation period in which all calves were offered low K, experimental diets (Table 1) were fed for 8 wk. Potassium concentration was increased via the addition of KCl rather than KHCD3 or K2CD3 to eliminate confounding effects of altering the cationanion balance. Individual feed intake was recorded daily and averaged by week; BW were recorded weekly. Feed samples were collected weekly and composited upon completion of the study for nutrient analysis at a commercial
Feed Intake and
Weight Gain We observed no NaHCD3 by K interactions for feed intake or weight gain (Table 2); feed intake was not affected by dietary K or NaHCD3 concentration during any individual week, or as the average response during the last 4 wk of the study. Using a similar diet, Well et aI. (23) reported that feed intake increased (P < .05) as dietary K was increased from .34 to .58% of OM. Intake was lower for their .58% K diet than for the .6% K diets, but their calves were several wk younger. Covariate-adjusted BW (Table 2) were greater for increased dietary K during wk 4 to 8; BW tended to be reduced by supplemental dietary NaHCD3 throughout the study. As a result. ADO (Table 2) increased as dietary K was increased from .4 to .6%, but ADO tended to decrease with supplemental NaHCD3. Well et al. (23) indicated that the K requirement of the growing dairy calf is in the range of .34 to .58% of diet OM and reported increased AOO as dietary K increased from .34 to .58% of diet Journal of Dairy Science Vol. 74, No.7, 1991
2298
TUCKER ET AL.
TABLE 1. Ingredient and OIltrient composition of experimental diets. Diet .4% K 0% NaHCO]
Ingredient:
SheDed com, cracked Dried brewers gnIin Oat grain, dry roDed Cottonseed hulls Soybean meal Limestone Dicalcium phosphate Potassium chloride Dynamate 1 Sodium chloride Magnesium oxide Vitamin ADE premix2 Sodium bicarbonate Calcium chloride3
.4% K 2% NaHCO]
.6% K 0% NaHC03
.6% K 2% NaHC03
- - - - - - - - (% DM) - - - - - - - 34.14 34.30 35.00 34.83 33.26 33.42 34.10 33.94 14.63 14.70 15.00 14.93 9.17 9.21 9.40 9.36 4.49 4.60 4.51 4.58 1.05 1.09 1.13 1.10 .39 .39 .40 .40 .51 .02 .50 .07 .06 .06 .en .16 .16 .16 .16 .07 .06 .07 .06 .05 .06 .05 .06 2.00 2.00 .03 .03 .03 .03
Nutrient4
NEro. 5
Mcal/kg
NDF Ca
P Mg Na K
a S
(Na
92.40 17.00 1.73
1.11
1.11
18.00 41.50 .69 .48 .19 .08 .35 .18 .24
17.40 35.70 .55 .47 .19 .08 .61 .34 .23
17.50 26.30 .43 .42
12.21
23.34
11.02
20.16
1.11
~f Mcal/kg
+ K) - C1, meq/loo g diet DM
91.60 16.00 1.73
91.60 14.40 1.70 1.09 19.60 37.50 .46 .43 .17 .30 .42 .17 .20
91.60 17.40 1.73
DM CP
.17
.31 .53 .38 .21
lDouble sulfate of K and Mg. 2Contains 4.540,000 1U vitamin A; 1,000,000 1U vitamin 0); and 500 1U vitamin E per .454 kg.
3Product contains 95% calcium chloride. 4Composition from laboratory analyses. 5NEro
= Net
energy for maintenance; NEg
= net
energy for gain.
DM, but in a separate experiment, they observed no growth response to increasing dietary K from .55 to .84%. The faster rate of growth observed in the present study in response to increasing dietary K from .4 to .6%, when contrasted with the lack of growth response to increasing dietary K from .55 to .84% (23), indicates that the K requirement for growth of young calves is between .4 and .55% of DM. In both studies, ADO appeared to be more useful than feed intake as an indicator of the adequacy of K. The tendency for ADO to be suppressed by dietary NaHC03 supplementation contrasts Journal of Dairy Science Vol. 74, No.7, 1991
with the results of Cumick et al. (4), who detected no postweaning effects on ADO, and with findings by Hart and Polan (8) and Kellaway et al. (12), who reported that ADO increased in response to dietary NaHC03 supplementation. Minerals In Plasma and Urine, and Urine pH
Plasma Na (Table 3) averaged across the final three sampling times was greater when dietary K was supplemented, but no effect of K on urinary Na excretion was observed
TABLE 2. Least squares means and orthogonal contrasts for feed intake, BW. and average daily gain (ADO). .35% K 0% NaHC03 Feed intake,l kg Weekl 4 to 8
[ ... 0
E !' r.n
n
~
4.41
.42% K 2% NaHCOJ
3.96
.61% K 0% NaHC03
4.32
.53% K 2% NaHC03
4.33
K
SE
.24
Low
4.19
NaHC03 High
4.32
SE
.17
Low
4.36
Effect,
High
4.14
SE
.17
BW,kg Week 0 2 4 6
78.9 88.4 97.4 111.6
77.0 87.1 97.3 1082
69.9 89.1 100.5 115.4
77.6 88.7 99.0 113.1
3.6 1.2 1.4 1.7
77.9 87.8 97.4 109.9
73.7 88.9 99.8 114.3
2.5 .8 1.0 12
74.4 88.7 99.0 113.5
77.3 87.9 98.2 110.7
2.5 .8 1.0 12
8 4 to 8
122.9 117.3
121.0 114.6
130.1 122.7
128.0 120.6
22 1.7
121.9 115.9
129.0 121.6
1.5 12
126.5 120.0
124.5 117.6
1.5 1.2
ADO, kg Week 0 2 4 6 8 4 to 8
P
r.n
~
~ ~
K, .11 K, .02 Na, .10 Ie, .005 Ie, .004
~
! 0 Z
.90 .64 1.02 .81 .91
.81 .73 .78 .91
.95 .82 1.06 1.05
.84
LOS
.92
.08
.74 1.01 1.06 1.03
.10 .10 .13
.08
.85 .69
.90 .86 .88
.93 .78 1.03 1.06 1.04
.06 .07 .07 .09 .05
.92 .73 1.04 .93 .98
.86 .73 .89 .99 .94
.06 .07 .07 .09 .05
Na, .15 1e,.04
~
r.n
~
1As-fed basis. 2Week of study.
"j.
~ ;-l
~
N N
~
2300
TUCKER ET AL.
These results contradict those of Well et al. (23), who reported that increasing dietary K from .34 to .58% of DM tended to decrease plasma Na. In the present study, urinary Na excretion increased with increased dietary NaHC03 concentration. Plasma K (fable 3) was increased by supplemental dietary K during wk 4 to 8; this elevation (5.71 vs. 5.24 meq/L, SE =.136) was evident by wk 2. Plasma K has been responsive to dietary K in some studies (5, 21) but not in others (17, 23). During wk 4, supplemental NaHC0 3 increased plasma K for calves receiving the low K diet, but it decreased plasma K for calves receiving the high K diet, yielding a NaHC03 x K interaction. However, this pattern was not observed at any other sampling time. Both dietary K and NaHC03 increased urinary K excretion, a response that was evident by wk 4 for K and by wk 8 for NaHC03' In studies with mature lactating cows, Tucker and Hogue (21) reported that supplemental dietary KO, but not NaO, increased urinary K excretion; Rogers et al. (15) observed an increase in fractional excretion of K in response to dietary supplementation of 1.2% NaHC03. Increased urinary K excretion in response to dietary NaHC03 supplementation likely can be attributed to the diuretic effect of excess Na Plasma CI (fable 3) was elevated by supplemental dietary KCI during wk 4 to 8 and tended to be increased throughout the study. Others (3, 6, 20) have reported that plasma Cl is responsive to dietary 0 concentration. Urinary 0 excretion was increased by dietary KCl but tended to be reduced (P = .11) by dietary NaHC03. This is in contrast with Rogers et al. (15), who reported that 1.2% NaHC03 increased urinary CI excretion. Plasma Ca (fable 3) was generally not affected by diet, although supplemental K increased plasma Ca (5.43 vs. 5.21 meq/L, SE = .076) during wk 2. Urinary Ca excretion was not affected by dietary K, but it was decreased by supplemental dietary NaHC03 throughout the study. However, this effect is confounded by the dietary Ca concentrations, which were unintentionally lower for the 2 versus 0% NaHC03 diets. A reduction in urinary Ca excretion is a typical response to elevated dietary Na or K. Takagi and Block (18) reported that increasing the dietary cation-anion balance Journal of Dairy Science Vol. 74, No.7, 1991
i•. "0
"''0
plemented with NaHC03, and 3) average daily gain and plasma K are sensitive indicators of dietary K in the growing calf. (Key words: potassium, sodium, dairy calf growth, feed intake)
We evaluated the influence of supplemental dietary NaHC03 on K metabolism of young dairy calves. Thirty-two Holstein and Jersey male and female calves were blocked at 56 to 70 dafter birth according to breed, sex, and age and assigned randomly to a 2 x 2 factorial arrangement of dietary treatments for 8 wk: .4% K with 0% NaHC03, .4% K with 2% NaHC03, .6% K with 0% NaHC03, and .6% K with 2% NaHC03. Feed intake was not affected by dietary KCI or NaHC03 supplementation, but average daily gain increased with increased K and tended to be reduced by dietary NaHC03. Plasma K was elevated by increased dietary K but generally was unaffected by NaHC03. Urinary Ca excretion appeared to be reduced by NaHC03; urine pH increased with supplemental NaHC03' Results indicate 1) the K requirement of the growing calf is between .40 and .55% of diet DM, 2) because urinary K excretion was elevated by dietary NaHC03, the K requirement may be increased when the diet is sup-
Abbreviation key: ADG = average daily gain. INTRODUCTION
Received July 23, 1990. Accepted December 6. 1990. IThis manuscript (90-5-128) is published wilh !he approval of the director of the Kentucky Agricultural Ex~riment Station. 2Joumal Article 5792 of the Oklahoma State Agricul~ E~rime~lt Station, StiUwaler 74078. Animal SCIence Department, 01daboma Stale University. Stillwater 74078. '70 whom requests for reprints should be addressed. SDepartment of Anima1 Science, University of Kentucky, Lexington 40546. 1991 J Dairy Sci 74:2296-2302
Historically, ruminants consumed diets high in K-rich forages and, as a result, should have encountered few problems with K deficiencies. In recent years, however, the trend to supplement the diets of dairy animals with proportionately more grain has established K as a potentially limiting nutrient. By-products of the distillery and brewery industries contain less K than forages; when constituting a major porti~n of the diet, they can reduce markedly the dietary K concentration. Well et al. (23) evaluated the K requirement of growing dairy calves and reported that it was between .34 to .58% of diet DM This range is slightly below the .65 to .8% requirement listed for beef cattle (1~) and the .9 to 1% needed for lactating dairy cattle (14) but is similar to the requirement of lambs (.3 to .5%) (2) and higher than concentrations required by chicks (.23 to .40%) (1), young pigs (.26%) (9), and rats (.18%) (7). Although a dietary range has been established for the K requirement of growing dairy calves, the impact of other dietary constituents on this requirement remains to be identified. The ability of dietary buffers to replace the ~eficit in rumen buffering capacity caused by madequate saliva production in young calves has been investigated (8). In Australia, increased growth rate and feed intake were re-
2296
SODWM BICARBONATE EFFECTS ON POTASSIUM
ported with the addition of both 2 and 4% NaHCD 3 to pelleted diets (10); these results were confmned by Kellaway et al. (11) with diets containing either a mixture of 2% NaHCD 3 and 2% NaHP04 , or 4% NaHCD3. More recently, Hart and Polan (8) reported that average daily gain (ADG) was maximized with diets containing between 1 and 2% NaHCD3; higher amounts of buffer tended to reduce performance. Because dietary Na increases with NaHC03 addition, the effects of Na on K metabolism in growing dairy calves need to be evaluated. In nonruminants, high dietary Na intake increases renal K excretion by increasing the flow rate in the late distal tubules and cortical collecting ducts of renal nephrons, thus creating a larger gradient for the diffusion of K into the tubular lumen (22). This response also has been observed in lactating dairy cattle by Rogers et al. (15), who reported an increase (P = .11) in fractional excretion of K when NaHCD3 was fed at 1.2% of diet OM. The objective of this trial was to evaluate the effects of dietary NaHCD 3 on K metabolism in growing dairy calves.
2297
laboratory. Urine, collected via stimulation of the vulva for females and sheath for males at wk 0, 2, 4, 6, and 8, was analyzed for creatinine and then acidified with 3% concentrated HCl. Blood was collected at 0900 h at 0 d and every 14 d thereafter via jugular venipuncture into heparinized, evacuated glass tubes, and centrifuged. Plasma was harvested into clean, polypropylene tubes and frozen for subsequent mineral analyses. Blood plasma and urine Na, K. Ca, and Mg were analyzed via atomic absorption spectrophotometry (Model 4000, Perkin-Elmer Corp., Model 4000, Norwalk, CT) and Cl was analyzed via potentiometric titration (Haake-Buchler Instruments, Inc., Saddlebrook, NJ). Oata were analyzed according to the general linear models procedure of SAS (16); the model included variation due to blocks, dietary K, NaHCD3. the K x NaHCD3 interaction, and residual error. Treatment means and interactions were compared using orthogonal contrasts. Week 0 observations were utilized as covariates for BW and plasma minerals. Significance was declared at P < .10 unless otherwise noted. RESULTS AND DISCUSSION
MATERIALS AND METHODS
Twenty-four Holstein (8 male, 16 female) and 8 Jersey female calves were weaned at 6 wk of age and offered a calf starter concentrate. After intake of the starter reached .9 kg/d (56 to 70 d of age), calves were blocked according to breed, sex, and age and assigned randomly to a 2 x 2 factorial arrangement of dietary treatments: .4% K with 0% NaHCD3, .4% K with 2% NaHCD 3, .6% K with 0% NaHCD3' and .6% K with 2% NaHCD3. After completion of the study, treatment groups were analyzed and found to contain .35, .42, .61, and .53% K, respectively (OM basis). After an initial l-wk adaptation period in which all calves were offered low K, experimental diets (Table 1) were fed for 8 wk. Potassium concentration was increased via the addition of KCl rather than KHCD3 or K2CD3 to eliminate confounding effects of altering the cationanion balance. Individual feed intake was recorded daily and averaged by week; BW were recorded weekly. Feed samples were collected weekly and composited upon completion of the study for nutrient analysis at a commercial
Feed Intake and
Weight Gain We observed no NaHCD3 by K interactions for feed intake or weight gain (Table 2); feed intake was not affected by dietary K or NaHCD3 concentration during any individual week, or as the average response during the last 4 wk of the study. Using a similar diet, Well et aI. (23) reported that feed intake increased (P < .05) as dietary K was increased from .34 to .58% of OM. Intake was lower for their .58% K diet than for the .6% K diets, but their calves were several wk younger. Covariate-adjusted BW (Table 2) were greater for increased dietary K during wk 4 to 8; BW tended to be reduced by supplemental dietary NaHCD3 throughout the study. As a result. ADO (Table 2) increased as dietary K was increased from .4 to .6%, but ADO tended to decrease with supplemental NaHCD3. Well et al. (23) indicated that the K requirement of the growing dairy calf is in the range of .34 to .58% of diet OM and reported increased AOO as dietary K increased from .34 to .58% of diet Journal of Dairy Science Vol. 74, No.7, 1991
2298
TUCKER ET AL.
TABLE 1. Ingredient and OIltrient composition of experimental diets. Diet .4% K 0% NaHCO]
Ingredient:
SheDed com, cracked Dried brewers gnIin Oat grain, dry roDed Cottonseed hulls Soybean meal Limestone Dicalcium phosphate Potassium chloride Dynamate 1 Sodium chloride Magnesium oxide Vitamin ADE premix2 Sodium bicarbonate Calcium chloride3
.4% K 2% NaHCO]
.6% K 0% NaHC03
.6% K 2% NaHC03
- - - - - - - - (% DM) - - - - - - - 34.14 34.30 35.00 34.83 33.26 33.42 34.10 33.94 14.63 14.70 15.00 14.93 9.17 9.21 9.40 9.36 4.49 4.60 4.51 4.58 1.05 1.09 1.13 1.10 .39 .39 .40 .40 .51 .02 .50 .07 .06 .06 .en .16 .16 .16 .16 .07 .06 .07 .06 .05 .06 .05 .06 2.00 2.00 .03 .03 .03 .03
Nutrient4
NEro. 5
Mcal/kg
NDF Ca
P Mg Na K
a S
(Na
92.40 17.00 1.73
1.11
1.11
18.00 41.50 .69 .48 .19 .08 .35 .18 .24
17.40 35.70 .55 .47 .19 .08 .61 .34 .23
17.50 26.30 .43 .42
12.21
23.34
11.02
20.16
1.11
~f Mcal/kg
+ K) - C1, meq/loo g diet DM
91.60 16.00 1.73
91.60 14.40 1.70 1.09 19.60 37.50 .46 .43 .17 .30 .42 .17 .20
91.60 17.40 1.73
DM CP
.17
.31 .53 .38 .21
lDouble sulfate of K and Mg. 2Contains 4.540,000 1U vitamin A; 1,000,000 1U vitamin 0); and 500 1U vitamin E per .454 kg.
3Product contains 95% calcium chloride. 4Composition from laboratory analyses. 5NEro
= Net
energy for maintenance; NEg
= net
energy for gain.
DM, but in a separate experiment, they observed no growth response to increasing dietary K from .55 to .84%. The faster rate of growth observed in the present study in response to increasing dietary K from .4 to .6%, when contrasted with the lack of growth response to increasing dietary K from .55 to .84% (23), indicates that the K requirement for growth of young calves is between .4 and .55% of DM. In both studies, ADO appeared to be more useful than feed intake as an indicator of the adequacy of K. The tendency for ADO to be suppressed by dietary NaHC03 supplementation contrasts Journal of Dairy Science Vol. 74, No.7, 1991
with the results of Cumick et al. (4), who detected no postweaning effects on ADO, and with findings by Hart and Polan (8) and Kellaway et al. (12), who reported that ADO increased in response to dietary NaHC03 supplementation. Minerals In Plasma and Urine, and Urine pH
Plasma Na (Table 3) averaged across the final three sampling times was greater when dietary K was supplemented, but no effect of K on urinary Na excretion was observed
TABLE 2. Least squares means and orthogonal contrasts for feed intake, BW. and average daily gain (ADO). .35% K 0% NaHC03 Feed intake,l kg Weekl 4 to 8
[ ... 0
E !' r.n
n
~
4.41
.42% K 2% NaHCOJ
3.96
.61% K 0% NaHC03
4.32
.53% K 2% NaHC03
4.33
K
SE
.24
Low
4.19
NaHC03 High
4.32
SE
.17
Low
4.36
Effect,
High
4.14
SE
.17
BW,kg Week 0 2 4 6
78.9 88.4 97.4 111.6
77.0 87.1 97.3 1082
69.9 89.1 100.5 115.4
77.6 88.7 99.0 113.1
3.6 1.2 1.4 1.7
77.9 87.8 97.4 109.9
73.7 88.9 99.8 114.3
2.5 .8 1.0 12
74.4 88.7 99.0 113.5
77.3 87.9 98.2 110.7
2.5 .8 1.0 12
8 4 to 8
122.9 117.3
121.0 114.6
130.1 122.7
128.0 120.6
22 1.7
121.9 115.9
129.0 121.6
1.5 12
126.5 120.0
124.5 117.6
1.5 1.2
ADO, kg Week 0 2 4 6 8 4 to 8
P
r.n
~
~ ~
K, .11 K, .02 Na, .10 Ie, .005 Ie, .004
~
! 0 Z
.90 .64 1.02 .81 .91
.81 .73 .78 .91
.95 .82 1.06 1.05
.84
LOS
.92
.08
.74 1.01 1.06 1.03
.10 .10 .13
.08
.85 .69
.90 .86 .88
.93 .78 1.03 1.06 1.04
.06 .07 .07 .09 .05
.92 .73 1.04 .93 .98
.86 .73 .89 .99 .94
.06 .07 .07 .09 .05
Na, .15 1e,.04
~
r.n
~
1As-fed basis. 2Week of study.
"j.
~ ;-l
~
N N
~
2300
TUCKER ET AL.
These results contradict those of Well et al. (23), who reported that increasing dietary K from .34 to .58% of DM tended to decrease plasma Na. In the present study, urinary Na excretion increased with increased dietary NaHC03 concentration. Plasma K (fable 3) was increased by supplemental dietary K during wk 4 to 8; this elevation (5.71 vs. 5.24 meq/L, SE =.136) was evident by wk 2. Plasma K has been responsive to dietary K in some studies (5, 21) but not in others (17, 23). During wk 4, supplemental NaHC0 3 increased plasma K for calves receiving the low K diet, but it decreased plasma K for calves receiving the high K diet, yielding a NaHC03 x K interaction. However, this pattern was not observed at any other sampling time. Both dietary K and NaHC03 increased urinary K excretion, a response that was evident by wk 4 for K and by wk 8 for NaHC03' In studies with mature lactating cows, Tucker and Hogue (21) reported that supplemental dietary KO, but not NaO, increased urinary K excretion; Rogers et al. (15) observed an increase in fractional excretion of K in response to dietary supplementation of 1.2% NaHC03. Increased urinary K excretion in response to dietary NaHC03 supplementation likely can be attributed to the diuretic effect of excess Na Plasma CI (fable 3) was elevated by supplemental dietary KCI during wk 4 to 8 and tended to be increased throughout the study. Others (3, 6, 20) have reported that plasma Cl is responsive to dietary 0 concentration. Urinary 0 excretion was increased by dietary KCl but tended to be reduced (P = .11) by dietary NaHC03. This is in contrast with Rogers et al. (15), who reported that 1.2% NaHC03 increased urinary CI excretion. Plasma Ca (fable 3) was generally not affected by diet, although supplemental K increased plasma Ca (5.43 vs. 5.21 meq/L, SE = .076) during wk 2. Urinary Ca excretion was not affected by dietary K, but it was decreased by supplemental dietary NaHC03 throughout the study. However, this effect is confounded by the dietary Ca concentrations, which were unintentionally lower for the 2 versus 0% NaHC03 diets. A reduction in urinary Ca excretion is a typical response to elevated dietary Na or K. Takagi and Block (18) reported that increasing the dietary cation-anion balance Journal of Dairy Science Vol. 74, No.7, 1991
i•. "0
"''0
