EFFECTS OF LIMESTONE AN D SODIUM BICARBONATE BUFFERS
ON RUMEN MEASUREMENTS A N D RATE OF
PASSAGE IN CATTLE
G. L. Haaland 1'2'3 and H. F. Tyrrell 1
US Department of Agriculture, Beltsville, MD 20705
Summary
Introduction
Eight rumen-fistulated cattle (four Angus
steers and four nonlactating Holstein cows)
were fed a cracked corn-based concentrate
(65% of dry matter) and corn silage (35% of
dry matter) diet containing: (1) no buffer,
(2) 2.5% limestone, (3) 2% sodium bicarbonate
(NaHCO3) or (4) 1.25% limestone and 1.25%
NaHCO3. Each diet was fed at approximately
maintenance and-two times maintenance levels
of intake, resulting in eight treatments in a
Latin square design. Buffer treatments had no
effect (P>.10) on rumen fluid pH, rumen
ammonia N concentration, total volatile f a t t y
acid (VFA) concentration or rumen buffering
capacity between pH 7.0 and 5.5. Rate of disappearance of solid and liquid fractions from
the rumen was measured using Cr-labeled dietary fiber and Co-EDTA, respectively. Rate of
disappearance was n o t significantly affected by
treatments, although liquid disappearance rate
was 7% faster with buffer treatments than with
the control. Fecal pH was increased (P<.01)
approximately . 5 units by all buffer treatments.
Increasing intake to two times maintenance
resulted in lower rumen pH (6.03 vs 6.37),
increased total V F A concentration (115 vs 99
retool/liter), increased rate of liquid disappearance from the rumen (6.6 vs 5.8%/h) and decreased concentration of Cr in the dry matter
fraction of the rumen contents (all P<.O1).
( K e y Words: Rumen, Buffer, Intake, Rate of
Passage, Rumen pH, Buffering Capacity.)
Responses to buffers have been variable and
unpredictable. Buffers can be beneficial when
diets produce an unfavorably low pH of digestive tract contents (Emerick, 1976; Mertens,
1979), which can occur with rapidly degradable
grain diets and fermented feeds. Diets that do
not produce unfavorable digestive tract conditions would n o t be expected to be improved by
buffers. Even with this explanation, responses
to buffers are variable and seem to indicate a
mode of action other than or in addition to a
change in pH of the digestive tract contents.
The inclusion of buffers in diets may increase
the rate of disappearance of liquid material
from the rumen due to passage as a result of
osmotic action (Harrison et al., 1975). Kellaway et al. (1978) reported that rate of liquid
disappearance was increased when sodium bicarbonate (NaHCO3) was included in the diet,
but they did not account for effects of intake
on rate.
The purpose of this experiment was to compare the effects of limestone and NaHCO3 in
corn-corn silage diets fed at two levels of intake
on rumen fluid pH, ammonia N (NH3-N),
volatile fatty acid (VFA) concentration, buffering capacity, rate of disappearance of solid and
liquid material from the rumen and fecal pH.
Materialsand Methods
Eight rumen-fistulated cattle (four Angus
steers, mean weight 500 kg, and four nonlactating Holstein cows, mean weight 600 kg)
were fed four diets (table 1) at approximately
Ruminant Nutrition Laboratory, Animal Science
maintenance (1 • M, .110 Meal metabolizable
Institute, ARS, S&E, Beltsville, MD 20705.
energy/body weight "75) or two times the estizThe authors gratefully acknowledge the assistance
of R. L. Brocht, R. Spencer, F. E. Sweeney and K. mated maintenance level of intake (2 x M) in
DeCesaris for animal care; E. L. Yoder and T. B. an 8 x 8 Latin square design. Metabolizable
Jacobs, Jr. for sampling and chemical analyses and
energy (ME) of the diet was calculated from
P. C. Marcus for data handling.
NRC (1976). Diet dry matter (DM) consisted
3Dr. Haaland passed away suddenly on March 29,
1982.
of 55% cracked corn, 35% corn silage and 10%
935
JOURNAL OF ANIMAL SCIENCE, "Col. 55, No. 4, 1982
936
HAALAND AND TYRRELL
of a pelleted supplement containing ground
corn, soybean meal and (1) no buffer (C),
(2) 25% limestone. (L), (3) 20% NaHCO3 (SB)
or (4) 12.5% limestone and 12.5% NaHCO3
(L-SB). Animals were fed twice daily at 12-h
intervals for 14 d, and measurements were
taken on the last 4 d. On d 11, samples of
rumen contents were taken from the reticular
area of the reticulorumen 4 h postfeeding. The
samples were strained through four layers of
cheesecloth and pH was determined immediately using a combination electrode. A subsample of rumen fluid was placed in a tefloncapped vial and frozen for subsequent VFA
analysis; another sample was placed in a vial
containing 6 N HCI, resulting in a rumen fluid
to acid ratio of 9 to 1, and frozen for subsequent NH3-N analysis. Rumen fluid buffering
capacity was measured within 1 h of sampling
using 40 ml of strained rumen fluid. Rumen pH
also was measured On unstrained rumen samples
taken on d 12 at 0, 2, 4, 6 and 8 h postinfusion. Five fecal grab samples were taken over 12
h on d 12 from the four cows, and pH was measured on the composite from each cow. Solid
passage was measured with Cr-labeled fiber and
liquid passage was measured with cobaltethylenediamine tetra acetic acid (Co-EDTA)
on d 12 to 14.
Procedures for measuring fecal pH and
rumen fluid concentration of VFA, NHs-N and
buffering capacity have previously been described (Haaland et al., 1982).
The Cr-labeled fiber was prepared by the
extraction of solubles from the mixed diet with
neutral detergent fiber solution (Goering and
Van Soest, 1970). The remaining fiber was
added to a solution of Na2Cr207 such that Cr
was 10% of the fiber weight. The fiber was
boiled gendy in the Cr solution for 3 h, rinsed
with tap water and acetone and filtered through
a cloth sack (Uden, 1978). The dried fiber contained 2 to 3% Cr. The Co-EDTA complex was
made by combining a solution of 160 g of
EDTA dissolved with NH4OH to a solution containing 129 g of COC12"6H20 (Smith, 1968;
Uden, 1978). The resulting Co-EDTA solution
contained approximately 3% Co.
Fifty grams of Cr-treated fiber and 100 ml
of Co-EDTA were added to the tureen contents
of each animal on d 12, 2 h postfeeding and
hand-mixed. Samples of rumen contents were
taken before infusion and 2, 4, 6, 8, 26, 30 and
50 h postinfusion. Samples of 250 ml were
taken from the lower anterior, lower posterior,
upper posterior and upper anterior portions of
the rumen and composited. The samples that
contained both rumen liquid and particulate
TABLE 1. COMPOSITIONOF DIETS
Diet
Item
Control
Limestone
Sodium
bicarbonate
Cracked corn (IFN 4-02-931), %
Corn silage (IFN 3-08-154), %
55
35
55
35
55
35
Supplement
Limestone (IFN 6-02-632), %
Sodium bicarbonate, %
Dicalcium phosphate (IFN 6-01-O80), 96
Vitamin-mineral mix, %
Trace mineralized salt, %
Soybean meal (IFN 5-04-604), %
Ground corn (IFN 4-02-931), %
Gross energy, Mcal/kg
Metabolizable energy, Mcala
Crude protein, %
Neutral detergent fiber, %
Acid detergent fiber, %
Ash, %
aNRC, 1976.
.45
2.5
.66
.14
.50
2.81
5.36
4.54
2.96
10.5
26.4
12.3
4.1
Limestonesodium
bicarbonate
55
35
1.25
.66
.14
.50
2.81
3.31
.45
2.00
.66
.14
.50
2.81
3.36
.66
.14
.50
2.81
3.31
4.43
2.89
10.3
27.2
12.8
5.6
4.44
2.89
10.3
28.5
12.9
5.2
4.44
2.89
10.3
2%7
13.1
5.6
1.25
LIMESTONE AND SODIUM BICARBONATE
9 37
IN C A T T L E D I E T S
8
9~
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s
o
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e~
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mZ
.,4.
v
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938
HAALAND AND TYRRELL
matter as found in the rumen, were dried at 60
C and ground to pass through a l-ram screen.
The dried samples were placed in 2/5-dram vials
for neutron activation and counting of Cr and
Co in the same vial at the Nuclear Reactor
Laboratory, University of Wisconsin, Madison.
Dry matter content of the samples (48 h at 100
C) was determined at the time of filling vials.
Data were analyzed by procedures from the
General Linear Models package of the Statistical Analysis System (Barr et al., 1979). The
statistical model included as main effects dietary treatment, intake level, animal variation,
trial period and interactions of intake • dietary
treatment. Duncan's multiple range test was
used to evaluate mean comparisons. Concentrations of Cr and Co in rumen contents were
converted to natural logarithms for the calculation of rates of disappearance. Rates of marker
disappearance were obtained with the above
model using time within treatment or intake as
a covariable. Homogeneity of slopes was tested
by evaluating the significance o f time • treatment or time x intake level interactions.
Results and Discussion
There were no differences in rumen pH
(samples taken on d 11) associated with the
buffer treatments (table 2). Increases in rumen
pH have been reported with both NaHCO3
(Nicholson et al., 1963; Ralston and Patton,
1976) and limestone (Wheeler and Noller,
1976, 1977; Haaland et al., 1979), but in many
cases, pH has not been affected (Miller et al.,
1965; Loggins et al., 1968). Lack of response
may be associated with composition of the diet.
The corn in our experiment was coarsel)~ and
unevenly cracked, with approximately 20%
remaining as whole kernels. Whole and coarsely
ground corn would probably not be degraded as
rapidly or as completely as finely ground corn
and, therefore, would not result in as low a
rumen pH value. Galyean et al. (1979b) concluded that rumen pH and liquid outflow rates
of steers tended to increase with corn particle
size. Fecal pH was increased (P<.01; table 2)
by all buffer treatments, from 6.0 with the control (C) to 6.5. Reports from the literature indicate a consistent response in fecal pH to limestone (Wheeler and Noller, 1976, 1977; Bull et
al., 1978; Haaland et al., 1979). An increase in
fecal pH with NaHCO3 was unexpected considering the soluble nature of NaHCO3; however, similar responses have been observed (Bull
et al., 1978). Russell et al. (1980) reported a
tendency for fecal pH of feedlot cattle to
TABLE 3. EFFECT OF INTAKE ON pH, AMMONIA NITROGEN, VOLATILE FATTY ACID
CONCENTRATION AND BUFFERING CAPACITY OF DIGESTIVE CONTENTS
,,
,,
,
Intake level
Item a
Maintenance
Two
times
maintenance
Rumen pH
Fecal pH
Rumen NH3-N, mg/dl
Total VFA concentration, mmol/liter
Acetic, % of total
Prqpionic, % of total
Acetic/propionic
6.37 b
6.74 b
3.24 d
99 b
64.3 b
18.8 d
3.47 d
6.03 c
6.10 c
3.31 d
115 c
62.2 c
19.8 d
3.26 d
.029
,092
.240
1.5
.40
.37
.073
1.82 d
5.80 b
1.33 b
1.76 d
6.27 c
1.51 c
1.14 c
.045
.087
.024
.020
Buffering capacity, meq H+/40 ml
strained mmen fluid
pH 7.0 to 5.5
pH 7.0 to 3.0
pH 5.0 to 4.5
pH 4.5 to 4.0
.99 b
Standard
error
aEach Value represents the mean of 32 observations except fecal pH, where n = 16. Samples were taken on d
11 after initiation of treatment except fecal pH, where samples were taken on d 12.
b'CMeans in the same row without a common superscript differ (P<.01).
dMeans in the same row without a common superscript differ (P<.05).
LIMESTONE AND SODIUM BICARBONATE IN CATTLE DIETS
6.6
x control
939
x
9 NaHCO 3
i (5.4
9 ,imostono-.a.CO~ . . - . x
Z
rt limestone
~-~./"
X ~ : ~ / ~
9 6.2
6.0
z
<
"""=~"
r~
I
2
I
4
I
6
HOURS POST
I
8
r~
~Z
I
10
FEEDING
Figure 1. Effect of time postfeeding on tureen pH
evaluated by diet9 Each point represents the mean of
16 observations. Samples were taken on d 12 after
initiation of treatment.
<
<
increase with a NaHCO3 treatment, but noted
no change in rumen pH. Buffers could affect
fecal pH in different ways. Wheeler and Noller
(1977) have proposed that limestone aids in
buffering the intestinal tract, creating an increased fecal pH. Galyean et al. (1979a) and
Russell et al. (1980) reported indications that
buffers were allowing for increased ruminal
digestion of starch and less to be passed postruminally. Less starch in the lower tract would
reduce bacterial fermentation postruminally
and could account for the increased fecal pH.
Alternatively, limestone and NaHCO3 could
influence fecal pH by affecting rate of passage
of liquid material through the digestive tract 9
Rumen NH3-N concentrations were very low
with all treatments (table 2; <4 mg/dl). Pelleting of the supplement might have reduced the
degradation of soybean meal protein in the
tureen that produced the low rumen NH3-N
values. Increasing level of intake did not result
in a significant increase in NH~-N (table 3), as
reported by others (McIntyre, 1970).
Rumen pH (samples taken on d 11) decreased (P<.01) from 6.37 to 6.03 as intake increased from 1 x M to 2 x M (table 3). The pH
of rumen fluid (samples taken on d 12) decreased with time postfeeding (figure 1),
reaching a minimum value at 4 h postfeeding
that was similar to values reported by Reid et
al. (1957) and Erdman (1979).
Total concentration of V F A was not affected by treatment (P>.01; table 2). The proportion of propionate with the SB treatment
was slightly higher (P<.05) than the mean of
all other treatments. Generally, NaHCO3 is
associated with lower propionate levels, but
r~
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.,Q
r~
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940
HAALAND AND TYRRELL
there are also reports indicating that propionate
level increases (Reid et al., 1957i Nicholson et
al., 1963) with high concentrate diets. Van
Campen ( 1 9 7 6 ) a n d Davis (1979)attempted to
summarize the relationship of rumen pH to
molar proportion of fatty acids. Their conclusions show some disparity, emphasizing the
difficulty of making definitive statements.
Harrison et al. (1975) and Thomson et al.
(1978) reported a highly significant negative
relationship between rate of liquid disappearance from the rumen and propionate concentration. Possibly, NaHCO3 has a multiple effect on fermentation that influences molar
proportion of VFA, resulting in apparent variations in results. The concentration of total VFA
increased (P<.01) with increasing level if intake (from 99 mmol/liter at 1 x M to 115
mmol/liter at 2 x M; table 3).
Rumen buffering capacity (pH 7.0 to 5.5)
was not changed by diet (table 2). With all
diets, buffering capacity increased to a maximum between pH 5.0 and 4.5, which is the pK
for VFA. The L treatment increased (P<.01)
buffering between pH 5.0 and 4.0, compared
with all other treatments, with nonsignificant
differences at other pH intervals.
Rate of disappearance of solid material from
the rumen was not changed (P>.10) by treatment (3.1%/h, C; 3.6 L; 3.7 SB and 3.0, L-SB,
table 4). Mean Cr concentration of dried rumen
samples decreased with time (figure 2), however, Cr concentration of samples taken between feedings either remained constant or
increased with time. The increase or no change
Cr= 3.23% / h
~
3
0
O 1
.:
feeding times
T
9
T
~
T
9
ie~o
sb
HOURS FROM INFUSION TIME
Figure 2. Mean rate (%/h) of Cr and Co disappearance from the tureen. Each point represents the mean
of 64 observations.
in Cr concentration between feedings might be
a true observation rather than mixing or sampling error. Unlabeled feed particles would have
escaped from the rumen both by absorption
and passage down the tract. Labeled feed particles could only escape by passage down the
tract. This would tend to increase the concentration of Cr on a dry weight basis. Also, Crlabeled fiber was placed into the rumen as
original-sized feed particles and would be larger
at infusion time than the average size of unlabeled feed particles in the rumen. Because
larger feed particles would be passed from the
rumen more slowly than smaller feed particles,
there would be a tendency for an increase in Cr
concentration.
The Cr-labeled fiber was not digested as
rapidly as unlabeled fiber, as determined by the
nylon bag technique (percentage disappearance
TABLE 5. RATE OF DISAPPEARANCE a OF SOLID AND LIQUID MARKERS FROM THE
RUMEN AND CALCULATED QUANTITY OF SOLID AND LIQUID MATERIAL
IN THE RUMEN BY LEVEL OF INTAKE
Intake level
Two
item
Rate of disappearance of Cr (solid marker), .%/h
Dry matter quantity in rumen calculated from
Cr disappearance curve, g
Rate of disappearance of Co (liquid marker), %/h
Liquid volume in rumen calculated from
Co disappearance curve, liters
Maintenance
times
maintenance
Standard
error of
estimate
3.1 b
3.6 b
.15
3,900
5.8 b
4,500
6.6 c
.11
42.3
41.8
aEach rate value was calculated from seven measurements taken over a 50-h period on 16 observations.
b'CMeans in the same row without a c o m m o n superscript differ (P<.01).
LIMESTONE AND SODIUM BICARBONATE IN CATTLE DIETS
from the nylon bag after 24 h: 15% for Crlabeled fiber vs 65% for unlabeled fiber). The
technique, therefore, may underestimate the
actual rate of disappearance, but the same bias
would affect all treatments. The effect of level
of intake on r~te of disappearance of solid
material (table 5) was not statistically significant (3.6%/h, 2 x M; 3.1, 1 x M). The lack of a
demonstrated significant effect on disappearance could be a function of the errors associated with measuring disappearance rather
than a lack of true effect. An increased rate of
disappearance with increased intake was hypothesized, which could have an important effect
on extend and site of digestion. Concentration
of Cr was nearly 20% higher (P<.01) at 1 x M
than at 2 x M. Quantity of DM calculated to be
in the rumen decreased from 4,500 g at 2 x M
to 3,900 g at 1 x M. Digestibility of nutrients
has been shown to be higher at low levels of
intake than at high levels (Tyrrell and Moe,
1975; Haaland et al., 1980). More complete
digestion in the rumen would be expected with
the smaller quantity of DM.
The liquid marker declined uniformly with
time and was not noticeably affected by feeding time. Rate of disappearance of the liquid
marker was about 7% higher when buffers were
included in the diets (table 4), b u t the response
was not significant.
Data indicate that buffers tend to increase
rate of disappearance of liquid from the tureen,
although statistical significance is difficult to
demonstrate. One important reason for the
large variation about the mean is imperfect
marker mixing in the rumen and resultant
sampling errors. KeUaway et al. (1978) fed
diets containing 6% NaHCO3 or an equivalent
amount of Na as NaC1 and reported that, by
comparison with control values, there was no
change in rumen osmotic pressure or pH. The
NaHCO3 treatment produced a 28% nonsignificant increase in liquid disappearance rate compared with control and NaC1 treatments. Harrison et al. (1975) infused artificial saliva and
NaHCO3 into rumens of sheep and reported a
strong relationship between rumen osmotic
pressure and rate of liquid disappearance and a
weak relationship between pH and rate of
liquid disappearance. The variation in relationship of rate of liquid disappearance with other
measurements indicates that rate does not
solely depend on osmotic pressure, digestive
tract pH or buffering capacity, but probably is
dependent on many factors.
941
The rate of disappearance of Co from the
rumen was 13% faster (P<.01) in animals fed at
2 x M than in those fed at 1 x M (table 5).
Concentration of Co estimated at time 0, however, was not affected by level of intake.
Galyean et al. (1979a) reported a tendency for
a decrease in tureen liquid volume and a large
increase in liquid disappearance from the rumen
with a doubling of intake. The significance of
an increase in the amount of DM accompanied
by no change in liquid volume at the higher
level of intake is left to conjecture.
Changes in rate of disappearance of liquid
from the rumen would be expected to have an
effect on feed intake, site and extent of digestion, and composition of nutrients absorbed.
Although results are variable, buffers tend to
increase liquid disappearance rate. With bulklimiting diets, an increased disappearance rate
may allow for increased intake. An increase in
disappearance rate could shift more of the
digestion from the rumen to the intestine.
This may decrease apparent digestion, but
could increase efficiency of utilization of
absorbed nutrients.
Digestive tract pH and buffering capacity are
increased by buffers, if changes occur at all,
which in some cases may improve the environment for microbial and enzymatic activity. In
cases where buffers do not change pH, their
role could be to stabilize pH, allowing for further or faster digestion and acid build-up. The
relationship of disappearance rate, pH, buffering capacity and their effect on energy digestibility requires further clarification.
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