Effects of Potassium Carbonate and Sodium Bicarbonate on Rumen

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Effects of Potassium Carbonate and Sodium Bicarbonate on Rumen Powered By Docstoc
					Effects of Potassium Carbonate and Sodium Bicarbonate
on Rumen Function in Lactating Holstein Cows 1

                                                               J. W. WEST, 2 C. E. COPPOCK, D, H. N A V E ,
                                                                       J. M. L A B O R E , and L. W. G R E E N E
                                                                             Department of Animal Science
                                                                                                T. W. O D O M
                                                                                 Poultry Science Department
                                                                                      Texas A & M University
                                                                                       College Station 77843

                                                          buffer and serves as a potassium supple-
      Twelve muhiparous lactating Holstein                ment.
   cows were used to compare effects of 1)
   no buffer, 2) 1.5% sodium bicarbonate,                               INTRODUCTION
   3) 1.25% potassium carbonate, or 4)
                                                          An energy dense ration is required for cows
   1.85% potassium carbonate in total diet             to reach and maintain high milk yields. Predic-
   on tureen environment and liquid turn-
                                                       tion of production up to 15,875 kg per cow per
   over, dry matter intake and digestibility,
                                                       yr by the yr 2000 (29) ensures continued use of
   milk yield and composition, and blood
                                                       heavy concentrate feeding. Smith (24) indicated
   acid-base balance. Cows fed buffered
                                                       that these diets are economically sound with
   diets had greater dry matter intake and
                                                       increasing milk production.
   greater digestibility of dry matter, acid
                                                          High concentrate diets often depress rumen
   detergent fiber, and neutral detergent
                                                       pH, lower fiber digestibility (19, 25), and are
   fiber than controls. R u m e n pH was higher
                                                       associated with alterations of the microbial
   in cows fed buffers than in controls 2 to
                                                       population (28). Dietary buffers may prevent
   4 h postfeeding, b u t buffered diets were
                                                       depressions in rumen pH. R u m e n pH was
   not different. Rumen volume, osmolality,
                                                       greater for 6 to 8 h postfeeding in cows fed
   and liquid turnover were unaffected by
                                                       buffers vs. controls and resulted in greater fiber
   dietary treatment. Molar percentage of
                                                       digestibility (5, 25). Increased fiber digesti-
   rumen acetate was greater, propionate
                                                       bility creates space for greater feed intake,
   was less, and acetate :propionate ratio was
                                                       which has been noted with dietary buffers (5).
   greater in cows fed 1.85% potassium
                                                       Buffers increase rumen acetate and decrease
   carbonate compared with other treat-
                                                       rumen propionate and increase acetate to
   ments. There were no treatment effects
                                                       propionate (A:P) ratio (5, 25). Thomas and
   on milk yield, although milk fat percent-
                                                       Emery (27) reported a positive linear relation-
   age tended to be greater in buffered diets.
                                                       ship between rumen A:P ratios and milk fat
   Blood acid-base balance was not altered.
      Cows fed diets containing potassium
                                                          A diet high in soluble particles increases
   carbonate performed similarly to those
                                                       osmotic potential in the rumen, stimulates
   fed sodium bicarbonate. No adverse
                                                       water consumption, and draws fluid into the
   effects of potassium carbonate on rumen
                                                       rumen from surrounding tissues. More fluid in
   function or environment were observed.
                                                       the rumen contributes to greater turnover of
   Potassium carbonate is an acceptable
                                                       the fluid (and water-soluble) compartment of
                                                       the rumen contents. A more rapid dilution rate
                                                       induced by mineral salts increased molar
   Received June 2, 1986.                              percentage of acetate and decreased molar
   Accepted October 16, 1986.                          percentage of propionate (19). Increased
    ~Technicai Article 21661 by the Texas Agricul-     microbial yield occurs with faster dilution rate
tural Experiment Station.
    2Tom Slick Fellow; Present address: Department     (28). With greater fluid turnover in the rumen,
of Animal Science, University of Georgia, Coastal      soluble carbohydrates and proteins are more
Plain Station, Tifton 31793.                           likely to escape rumen degradation.

1987 J Dairy Sci 70:81-90                         81
 82                                             WEST ET AL.

   During heat stress, lactating dairy cows           conditions and individual feeding for 4 d, fol-
benefit from dietary K higher than current            lowed by four periods, each consisting of 7 d of
recommendations (23, 31). It is desirable to          adaptation to diet and a 9-d comparison period
evaluate compounds that provide both buffer-          (cP).
ing and potassium supplementation. Schneider              Complete rations were sampled the last 2 d
et al. (23) reported that cows offered feed           of each adjustment and the first 4 d of each CP.
containing KHCO3 had reduced feed intake and          Fecal grab samples were taken twice daily the
milk production. Herod et al. (10) compared           first 6 d of the CP. Fecal sampling was delayed
numerous buffers in vitro, and found K2CO3            2 d after feed sampling to approximate passage
was a stronger buffer (neutralizer) than KHCO3        time. Fecal samples were taken on a schedule
or NaHCO3. In a comparison of K2C03,                  advancing 2 h/d, to account for diurnal varia-
KHCO3, and NaHCO3, West et al. (30) found             tion, so that sampling was at 2400 and 1200 h
cows offered a diet containing K2 CO3 consumed        on d 1, 0200 and 1400 h on d 2, and advanced
more forage and complete ration feed than             similarly for the next 4 d. Feeds and fecal
cows fed other buffers, indicating its possible       samples were dried to constant weight at 55°C
effectiveness as a dietary buffer.                    in a forced air oven, allowed to air equilibrate,
   Objectives of this trial were to measure           composited by period, and ground through a
effects of K2 CO3 on rumen liquid dilution rate       2-mm screen for later analysis.
and turnover. We compared buffer effects on               Feeds were analyzed for Ca, Mg, K, and Na
tureen pH, osmolarity, and volatile fatty acids       by atomic absorption spectrophotometry (1)
(VFA) as a function of time and the effects of        and Cr by spectrophotometry (11). Acid
buffers on diet digestibility. Effects of buffers     detergent fiber and NDF were by methods of
on blood gases, blood acid-base balance, milk         Goering and Van Soest (8), and Kjeldahl
yield and composition, and feed dry matter
intake were determined.

                                                      TABLE 1. Composition of concentrates used in exper-
                                                      imental diets.
    Twelve multiparous lactating Holstein cows
 averaging 74 d (range of 20 to 135 d) postpartum                                           Amount in
 were used to compare treatments of 1) control                                              concentrate
 (no buffer), 2) 1.5% NaHCO3,3) 1.25% K2CO3,
 or 4) 1.85% K2CO3 in the total diet. With                                                  (%)
 1.25% K 2 CO3, the carbonate ion was present at     Ground corn                            55.82
 approximately half the concentration of the         Soybean meal                           36.00
bicarbonate ion in NaHCO3, producing a               Defluorinated phosphate                 2.00
                                                     Limestone                               1.20
theoretically equal ability to absorb hydrogen       Plain salt                                .40
ions on a weight basis. Using K2CO3 at 1.85%         Dyna-MateI                               .20
of the diet produced a theoretical hydrogen ion      T r a c e mineralized premlx 2           .20
absorption ability approximately 1.5 times that      Magnesium oxide                          .15
                                                     Vitamin premix 3                         .03
of 1.5% NaHCO3. Experimental treatments              Experimental premix4                    4.00
were carried in the concentrate (Table 1) as was
Cr203, an indigestible external marker. Cows             1Trade name, International Minerals Corp. A
were fed complete rations of 60% concentrate         double salt of potassium and magnesium sulfate.
and 40% corn silage (dry basis) for 4 h twice           2Contained Mn, 1.35%; Fe, 6.7%; Zn, 6.7%; Cu,
daily at 0800 and 2000 h.                            .67%; I2, .02%; Se, .0067%; Ca, 18.5 to 22%.
    Cows were divided randomly into four                3Vitamin A, 1,540,000 USP/kg; vitamin D,
                                                     660,000 UsP/kg; and vitamin E, 880 IU/kg.
groups of three and arranged in a 4 × 4 Latin           4Control diet 1, .25% chromic oxide and 3.75%
square design. Four cows were fitted with            ground corn; 1.5% NaHCO3 diet 2, .25% chromic
rumen cannulae with one cannulated cow               oxide, 2.5% NaHCO3, and 1.25% ground corn; 1.25%
assigned to each group and considered to be          K2CO~ diet 3, .25% chromic oxide, 2.08% K2CO3,
                                                     and 1.67% ground corn; and 1.85% K2CO3 diet 4,
renresentative of that group for intensive rumen     .25% chromic oxide, 3.08% K2CO3, and .67% ground
sampling. Cows were adjusted to experimental         corn.

Journal of Dairy Science Vol. 70, No. 1, 1987
                              EFFECTS OF BUFFERS ON RUMEN FUNCTION                                         83

nitrogen by methods of AOAC (2). Fecal                   extrapolation of PEG concentration to time 0
samples were analyzed for Cr, ADF, and NDF               and dividing the amount of PEG added to the
as described.                                            rumen b y the PEG concentration at time 0. The
    Milk was weighed and sampled twice daily 3           slope of the natural logarithm of PEG concen-
d during each CP, and daily composites were              tration was used to calculate rumen dilution
analyzed for fat and protein, 3 and somatic              rate.
cells. 4 Cows were weighed three times during                Data were analyzed using the general linear
each CP. Blood from the jugular vein and from            models procedure of SAS (22). The model for
the coccygeal artery was sampled 2 d during              all measurements except those associated
each CP. Venous blood was collected in heparin-          specifically with cannulated cows was Yijk = u
ized evacuated tubes from which plasma was               + C i + Pj + T k + Eijk, where u was the overall
harvested for Mg analysis (1). Arterial blood            mean; Ci, the cow effect; Pj, the period effect;
was drawn on d 7 and 9 o f each CP into chilled,         Tk, the effect o f buffers; and Eij k, the residual
heparinized, 5-ml syringes and stored in ice             error. Measurements across time associated with
until analyzed within 1 h b y a Corning blood            cannulated cows (i.e., rumen pH, osmolarity,
gas analyzer s for pH, base excess, bicarbon-            V F A concentration) were analyzed using the
ate, and blood gases.                                    repeated measures package o f SAS (22). Differ-
   Rumen fluid dilution rate was determined              ences between treatment means were determined
by measuring the disappearance of polyethylene           using least squares means.
glycol (PEG), a water-soluble marker. Cows
were infused at 0500 h with 100 g PEG (M r
                                                                    RESU LTS A N D DISCUSSION
3350) dissolved in 500 ml water. By means o f a
rubber tube fitted with a plastic funnel, the                  Chemical analyses of diets are in Table 2.
solution was added at numerous locations to              Diets low in fiber are often supplemented with
facilitate mixing with rumen contents. To                buffers to prevent fat test depression and
determine rate of PEG loss, rumen fluid samples          rumen disorders. Cows fed buffers ate more
were removed from ruminally cannulated cows              feed than controls, although dry matter intake
at 0600 h (immediately prior to feeding) and             for those fed 1.25 % K2 CO3 was not significantly
every 2 h until 1800 h b y rumen contents                different from controls (Table 3). Buffers have
aspirated through a rubber hose attached to a            increased feed intake in some studies (7, 12)
vacuum pump. Rumen fluid was filtered                    but not in others (5, 19). The amount of buffer
through double layers of cheesecloth, and                used in this study was relatively high b u t did
aliquots were frozen for later PEG, osmolality,          not depress feed intake. Period effects were
and V F A analysis. Rumen pH was measured                significant; cows consumed less total feed and
immediately after filtering. Volatile f a t t y acid     less as a percentage of b o d y weight in the
samples were acidified with 25% metaphosphoric           fourth period than in other periods. This trial
acid in a 1:4 acid:rumen fluid ratio before              extended from April 1 to June 3, 1985 with the
freezing for later V F A analysis (6). Osmolality        fourth CP being May 26 to June 3. During the
was b y vapor pressure osmometer. 6 Analysis             fourth period, maximum ambient temperature
for PEG was as described by Rogers et al. (19).          averaged 32.7°C, compared with 24.5,28.2, and
Concentration of PEG was converted to natural            28.4°C for 1, 2, and 3, respectively. McDowell
logarithm to determine rumen volume by                   (14) stated that lactating cows reduced feed
                                                         intake sharply above 30°C. This is supported b y
                                                         our findings.
                                                               Effects of buffer treatments on postprandial
                                                         rumen pH are in Figure 1. A significant time b y
                                                         t r e a t m e n t interaction occurred when pH at
   3 Milk-O-Scan 300. N. Foss Electric, Hillerod, Den-
mark.                                                    time 0 was compared with h 2 and 4, indicating
   4Fossomatic 15600. N. Foss Electric, Hillerod,        a response to treatments that changed with
Denmark.                                                 time. At h 2, rumen pH was higher in cattle fed
   SCorning 158 pH/Blood gas analyzer. Coming            buffered diets compared with that o f controls;
Ltd., Halstead, Essex, England.
   65100C Vapor Pressure Osmometer, Wescor, Inc.,        the numeric advantage for buffered diets
Logan, UT.                                               continued into h 4 and 6. Rumen pH was

                                                                 Journal of Dairy Science Vol. 70, No. 1, 1987




     TABLE 2. Chemical com p o s itio n o f d ie t ar y c o m p o n e n t s and c ompl e t e rations.

Z                                       Crude
     Item                               p r ote in           ADF 1              NDF 2              Calcium    Magnesium   Potassium   Sodium   Phosphorus

0Q                                                                                                            (%)
     Corn silage                          7.7                25.2               49.0                .20       .11          .85         .01     .22
      Control diet                      22.3                   7.0              23.6               1.33       .27          .99         .35     .94
      1.5% NaHCO a diet                 21.9                   6.8              27.3               1.35       .27         B.96        1.08     .88          r~
      1.25% K2CO s diet                 21.9                   6.9              28.8               1.28       .27         2.04         .35     .85
      1.85% K2CO a diet                 21.2                   7.0              29.7               1.23       .27         2.32         .35     .84
     C o m p l e t e rations
       Control                          16.6                 13.0               38.7                    .88   .19          .96         .23     .61
       1.5% NaHCO a diet                17.5                 13.0               34.7                    .92   .19          .93         .64     .67
       1.25% K 2 CO a diet              16.2                 13.9               36.3                    .82   .19         1.62         .22     .62
       1.85% K2CO a diet                16.3                 14.2               36.3                    .81   .19         1.98         .19     .60

         1 AD F = Acid detergent fiber.
         2 NDF = Neutral detergent fiber.
                                  EFFECTS OF BUFFERS ON RUMEN FUNCTION                                                                                        85

TABLE 3. Effect of buffers on dry matter intake and digestibility of diets.

                                                                1.5%                    1.25%                      1.85%
                                        Control                 NaHCO 3                  K2 3
                                                                                           CO                       K2 3
                                                                                                                      CO                                SE

Dry matter intake
 Total, kg/d                            20.7 b                  22.3 a                  21.5 ab                    22.0 a                                   .5
 kg/lO0 kg BW,1%                         3.5 b                   3.7 a                   3.6 ab                     3.7 a                                   .1
 kg/100 kg BW"Ts, %                     17.2 b                  18.5 a                  17.8 ab                    18.4 a                                   .4
Apparent digestibility 2
 Dry matter, %                          65.5 b                  68.8 a                  68.0 a                     67.7 a                                .7
 Acid detergent fiber, %                35.2 b                  44.8 a                  41.9 a                     43.7 a                               2.3
 Neutral detergent fiber, %             49.3 b                  56.0 a                  54.0 a                     55.8 a                               1.6

    a'bMeans within rows with different superscripts differ (P<.05).
    1 Body weight.
    2Adjusted using total dry matter intake during the comparison period as a covariate.

significantly depressed for all t r e a t m e n t s f r o m h      2% NaHCO3, or 2% l i m e s t o n e showed no
2 until h 8 c o m p a r e d w i t h h 0, and reached its           differences in r u m e n o s m o l a l i t y (19). Okeke et
lowest p o i n t at h 4, which was similar to that in              al. (16) n o t e d increased r u m e n o s m o l a l i t y 2 h
w o r k of Rogers et al. (19). Mertens (15) r e p o r t e d        p o s t f e e d i n g in lactating cows offered feed
t h a t fiber digestion is m a x i m u m at pH o f                 containing 2.5% NaHCO3. A significant increase
a p p r o x i m a t e l y 6.8 and declines rapidly as pH is        in m e a n r u m e n osmolality occurred at 2 h
reduced. R u m e n pH o f controls in our study                    postfeeding (Table 4), and a significant cubic
declined to a m i n i m u m of 5.64 (Figure 1), well               effect of r u m e n o s m o l a l i t y across t i m e was
b e l o w the range in which fiber digestibility is                noted. R u m e n o s m o l a l i t y r e t u r n e d to prefeeding
depressed. Digestibility o f dry matter, A D F ,                   values by 6 h p o s t f e e d i n g and was slightly less 8
and N D F was depressed in the control diet                        and 10 h postfeeding. There were no t r e a t m e n t
c o m p a r e d with buffer diets (Table 3). Means                 effects on r u m e n v o l u m e or r u m e n liquid
were adjusted using total dry m a t t e r intake as a
covariate, because dry m a t t e r intake m a y affect
digestibility (28). Digestibility and r u m e n pH
were similar a m o n g buffers (Table 3, Figure 1).                    6.8.

Others (5, 25) have n o t e d increased fiber
digestion with buffers. There was a significant
 cubic effect o f m e a n pH across t i m e and an
overall numeric advantage of r u m e n pH in
buffer-fed cows c o m p a r e d w i t h controls; cows             P   8.2,

fed 1.85% K2 CO3 had a higher pH than controls
 (P<.07). R u m e n pH r e t u r n e d to n o r m a l 10 h
postfeeding. A significant period e f f e c t showed                     5.9

r u m e n pH during period 4 was significantly
lower than during o t h e r periods.
      There was no significant t r e a t m e n t b y t i m e
interaction with r u m e n osmolality, and the
                                                                         E.E2          2             4
                                                                                                  HOUR8 POST FEEDING
                                                                                                                         . . . . . . . . . . . . . . . . . . . .

                                                                                                                                               E                   10

                                                                               LECENDI TRT               CONTROL                               1.2EX K2C03
o n l y significant t r e a t m e n t effect occurred at                                     ....        1 .EX NflHCO~
                                                                                                                               . . . . . . .

                                                                                                                               -----           1 .SEX K2CCI3

t i m e 0 (Table 4). Rogers et al. (20) reported
                                                                       Figure 1. Postprandial response of rumen pH to
greater r u m e n o s m o l a l i t y w h e n steers were           buffered diets. Treatments were control ( - - ) , 1.25%
infused with w a t e r containing .5 and 1.0 kg                     KaCO 3 (..... ), 1.5% NaHCO 3 (. . . . ), and 1.85%
NaC1, but cattle fed diets containing 2% NaC1,                      K2CO3 (------).

                                                                                Journal of Dairy Science Vol. 70, No. 1, 1987
86                                                                     WEST ET AL.

TABLE 4. Postprandial effects of buffers on rumen osmolality.

                                                                         Treatment 1
Hours                                                        1.5%                         1.25%                     1.85%
postfeeding                       Control                    NaHCO 3                      KzCO a                    K2COa                        Overall

                       SE           10.1                       10.i                         10.1                      10.1                         5.0
 0                                249.9 b                    284.5 a                      258-2ab                   280.7 a                      268.3 c•
 2                                318.5                      318.9                        310.7                     299.7                        312.0 d
 4                                302.4                      286.2                        302.0                     293.7                        296.1 d
 6                                266.2                      274.1                        257.6                     278.1                        269.0 c
 8                                238.0                      250.4                        252.6                     254.7                        248.9 d
10                                242.0                      251.6                        261.2                     254.1                        252.2 d
Overall                4.6        269.5                      277.6                        273.7                      276.9                       274.4

     a'bTreatment means within each time with different superscripts differ (P<.05).
     c'dMeans with different superscripts in the column differ (P<.05).
     * Significant cubic effect (P<.O009) of zero time means.

t u r n o v e r rate ( T a b l e 5). E f f e c t s o f m i n e r a l salts       V F A c o n c e n t r a t i o n d e c l i n e d (17, 18, 20). This
o n r u m e n liquid d i l u t i o n r a t e a n d t u r n o v e r t i m e       w a s likely d u e t o r e m o v a l o f s o l u b l e s u b s t r a t e s
have b e e n v a r i a b l e ; increases were n o t e d w i t h                  before they could be fermented, thus reducing
use o f NaC1 (19, 2 0 ) a n d n o e f f e c t s (5) or                           t o t a l V F A a n d p r o p i o n a t e p r o d u c t i o n . Increased
increased d i l u t i o n rate w i t h NaHCO3 (4). A                             m o l a r p e r c e n t a g e o f a c e t a t e results f r o m its
slight r e d u c t i o n in r u m e n v o l u m e was associated                 g r e a t e r c o n c e n t r a t i o n relative to p r o p i o n a t e .
w i t h an increased r u m e n fluid o s m o l a l i t y in                      A l t h o u g h n o c h a n g e in r u m e n d i l u t i o n rate
p e r i o d 4.                                                                   occurred,              similar r e s p o n s e s in V F A were
      G r e a t e r fluid t u r n o v e r in t h e r u m e n increased           o b s e r v e d in o u r w o r k ( T a b l e 6). T o t a l V F A
t h e rate o f r e m o v a l o f liquid s o l u b l e n u t r i e n t s ,        c o n t e n t was r e d u c e d using b u f f e r e d diets, a n d a
p a r t i c u l a r l y c a r b o h y d r a t e s . H a r r i s o n et al. (9)   greater molar percentage of acetate and reduced
i n d u c e d f e r m e n t a t i o n changes b y increasing                     m o l a r p e r c e n t a g e o f p r o p i o n a t e o c c u r r e d across
d i l u t i o n rate w i t h m i n e r a l salts w i t h o u t signifi-          t i m e w i t h 1.85% K2CO3 ( T a b l e 6). Molar
c a n t changes in pH, p r o b a b l y d u e t o m o r e rapid                   p e r c e n t a g e o f b u t y r a t e a n d A : P ratio was
r e m o v a l o f s u b s t r a t e s a n d m i c r o b e s in t h e fluid.      g r e a t e r w i t h t h i s d i e t a r y t r e a t m e n t (Table 6).
W h e n r u m e n liquid d i l u t i o n r a t e increased,                      T h e r e was a c u b i c e f f e c t o f m e a n t o t a l V F A
molar percentage of acetate and propionate                                       c o n c e n t r a t i o n across time, and m e a n s across
increased a n d decreased, respectively, a n d t o t a l                         t i m e were d i f f e r e n t f r o m t i m e 0 f r o m h 2 t o 8

TABLE 5. Effect of buffers on rumen liquid volume and turnover.

Rumen                                                                 1.5%                       1.25%                     1.85%
measurement                                Control                    NaHCO 3                    K 2CO 3                   K 2 CO s                  SE

Volume, L                                    60.3                       66.4                      62.4                       58.7                      6.5
Turnover rate, %/h                           14.6                       13.5                      14.7                       13.9                      1.2
Turnover, L/h                                 8.6                        8.6                       8.5                        8.1                       .5
Turnover, L/d                               207.1                      206.4                     205.0                      195.4                     12.5

Journal of Dairy Science Vol. 70, No. 1, 1987
                                         EFFECTS OF BUFFERS ON RUMEN FUNCTION                                                                 87

p o s t f e e d i n g ( T a b l e 6). T o t a l V F A   concentra-          prefeeding values 6 and 8 h postfeeding, respec-
tions peaked about 2 h postfeeding and returned                             tively. A cubic effect o f m o l a r percentage o f
t o p r e f e e d i n g c o n c e n t r a t i o n s a b o u t 8 t o 10 h    rumen butyrate was seen; percentage returned
postfeeding. Effects of mean molar percentages                              to prefeeding values 6 h postfeeding and
of acetate were cubic and of propionate were                                c o n t i n u e d d e c l i n e at 8 t o 10 h p o s t f e e d i n g
quadratic (Table 6); these effects returned to                              ( T a b l e 6). A s i g n i f i c a n t t i m e b y t r e a t m e n t

TABLE 6. Postprandial effects of buffers on r u m e n volatile fatty acids. Least squares means and standard errors

Hours                                                                      1.5%                1.25%            1.85%
postfeeding                               SE            Control            NaHCO z             K 2 CO 3         K 2 CO 3           Overall

Total VFA
                                          SE               7.8               7.8                   7.8             7.8                 3.9
  0                                                     105.9              110.4                99.2            116.6               108.1 c,**
  2                                                     147.7              148.4               138.0            136.5               142.7 d
  4                                                     146.8 a            132.5 ab            119.7 b          136.9 ab            134.0 d
  6                                                     133.1 a            125.1 ab            109.0 b          109.5 b             119.2 d
  8                                                     112.8              105.9                98.7             99.2               104.2 d
 10                                                      94.2               96.9                86.8             90.7                92.2 c
 Overall                                  1.7           123.4 a            119.9 ab            108.6 c          114.9 b             116.7
                                                                                              (molar %)
                                          SE               1.2               1.2                   1.2              1.2                  .6
  0                                                       55.7 b            52.8 b                54.9 b          59.1 a             55,6 d,* *
  2                                                       49.9 b            51.5 b                50.9 b          56.1 a             52.1 c
  4                                                       49.8 c            52.5 be               53.3 b          57.1 a             53.2 c
  6                                                       53.2 ab           53.8 ab               51.5 b          55.7 a             53.6 d
  8                                                       55.7 ab           57.4 a                52.5 b          56.2 a             55.5 d
 10                                                       57.7 a            54.4 ab               54.1 b          57.6 a             55.9 d
 Overall                                   1.5            53.7              53.7                  52.9            57.0               54.3
                                          SE                 .6                .6                   .6               .6                  .3
  0                                                       27.3 a            27.3 a                26.0 a          20.3 b             25.2c, t
  2                                                       29,2 a            27.5 a                27.4 a          22.9 b             26.7 d
  4                                                       30.8 a            28.0 b                27.3 b          22.8 c             27.2 d
  6                                                       31.3 a            27.9 b                29.8 a          23.6 c             28.1 d
  8                                                       29.7 a            26.4 b                29.0 a          23.2 c             27.1 d
 10                                                       28.0 a            27.2 a                27.5 a          22.3 b             26.2 c
 Overall                                   1.8            29.4 a            27.4 ab               27.8 ab         22.5 b             26.8
                                           SE                .7                .7                    .7              .7                  .3
  O*                                                      11.6 b            14.5 a                13.8 a          15.5 a              13.8 c'* *
  2                                                       15.6              16.0                  16.3            16.3                16.1 d
  4                                                       14.4              15.3                  14.5            15.5                14.9 d
  6                                                       11.1 c            14.0 ab               13.9 b          15.8 a              13.7 c
  8                                                       10.2              12.0                  13.3            15.2                12.7 d
 10                                                        9.6              13.3                  12.9            14.9                12.7 d
 Overall                                   1.0            12.1 b            14.2 ab               14.1 ab         15.5 a              14.0


                                                                                        Journal of Dairy Science Vol. 70, No. 1, 1987
88                                                              WEST ET AL.

TABLE 6. (continued) Postprandial effects of buffers on rumen volatile fatty acids. Least squares means and
standard errors (SE).

 Hours                                                                   1.5%                 1.25%            1.85%
 postfeeding                             SE               Control        NaHCO 3              KaCO 3           K2CO 3              Overall

Acetate :propionate ratio*
                                                                                           (molar ratio)
                                         SE                  .11            .11                    .11              .11                 .10
   0                                                        2.12 b         2.14 b                2.18 b            2.98 a              2.36 d,t
   2                                                        1.77 b         1.99 b                1.90 b            2.52 a              2.04 c
   4                                                        1.66 c         2.00 b                2.02 b            2.73 a              2.10 d
   6                                                        1.77 c         2.08 b                1.77 c            2.44 a              2.01 c
   8                                                        1.96 b         2.42 a                1.87 b            2.50 a              2.19 d
  10                                                        2.18 b         2.23 b                2.03 b            2.67 a              2.28 d
  Overall                                  .2               1.91 b         2.14 ab               1.96 b            2.64 a              2.16

     a'bTreatment means with different superscripts within each time differ (P<.05).
     C'dMeans with different superscripts within colums differ (P<.05).
     *Significant time X treatment interaction (P<.05).
     * *Cubic effect (P<.01) of zero time means across time.
     tQuadratic effect (P<.01) of overall means across time.

i n t e r a c t i o n o c c u r r e d at 2, 4, 8, and 10 h p o s t -      fat p e r c e n t a g e significantly g r e a t e r in cows fed
feeding.                                                                  1.85% K2CO3 vs. c o n t r o l s (Table 7). All
       R u m e n A : P ratios increased n u m e r i c a l l y b y         b u f f e r e d diets resulted in a n u m e r i c a l l y greater
buffer treatments compared with that of                                   milk fat p e r c e n t a g e , similar to t r e n d s n o t e d f o r
c o n t r o l s (Table 6) w i t h variable results across                 r u m e n A : P ratios (Table 6). G r e a t e r pH in
time. C o w s fed 1.85% K2CO3 had g r e a t e r A : P                     b u f f e r e d diets (Figure 1) and increased fiber
ratios overall.                                                           digestibility (Table 3) were associated w i t h t h e
      T h o m a s and E m e r y (27) r e p o r t e d a linear             g r e a t e r milk fat p e r c e n t a g e s n o t e d here. Total
r e l a t i o n s h i p b e t w e e n t h e A : P ratio and milk fat      solids t e n d e d t o b e g r e a t e r in c o w s fed b u f f e r e d
p e r c e n t a g e , a n d o t h e r s t u d i e s indicate increased    diets. N o o t h e r t r e a t m e n t e f f e c t s o n milk yield
milk fat p e r c e n t a g e w i t h increased A:P ratio (5,              or c o m p o s i t i o n were d e t e c t e d , .although milk
25). Results w e r e similar in this s t u d y w i t h m i l k            yield was less f o r c o w s fed K 2 C O 3 t h a n for

TABLE 7. Effect of buffers on milk yield and composition.

                                                                     1.5%                  1.25%                   1.85%
Milk component                                Control                NaHCO 3               K2CO 3                  K2CO 3                 SE

Yield, kg/d                                      28.0                 28.9                  26.2                     26.2                   .9
Fat, %                                            3.1 b                3.3 ab                3.3 ab                   3.5 a                 .1
3.5% FCM, * kg/d                                 25.6                 27.7                  24.8                     25.6                  1.0
Total solids, %                                  11.9 b               12.2 ab               12.2 ab                  12.3 a                 .1
Protein, %                                        3.3                  3.3                   3.3                      3.3                   .0
Fat yield, kg/d                                    .8                    .9                    .8                       .9                  .0
Protein yield, kg/d                                .9                    .9                    .8                       .8                  .0
Somatic ceils (X 1000)/ml                       160.8                153.6                 199.6                    166.6                 54.9

     a'bMeans within rows with different superscripts differ (P<.05).
     i Fat-corrected milk.

Journal of Dairy Science Vol. 70, No. 1, 1987
                                  EFFECTS OF BUFFERS ON RUMEN FUNCTION                                                      89

TABLE 8. Responses of blood parameters to buffer treatments.

                                                          1.5%                  1.25%               1.85%
Analysis                             Control              NaHCOz                K 2 CO 3              CO
                                                                                                    K2 3               SE

Blood pH                                7.49                7.50                  7.50               7.49               .005
Blood pCO2, mmHg                       37.37               38.16                 35.94              38.28               .85
Blood pO2, mmHg                        96.92               95.76                 98.62              94.87              3.18
Blood HCO3, meq/L                     28.28                29.39                 27.46              28.38               .52
Base excess, meq/L                     6.27 b               7.33 a                6.09 b             6.28 b             .34
Hematocrit, %                         28.96 ab             29.38 ab               30.02a            28.79 b             .32
Osmolality, mmol/kg                  277.19               278.59                277.38             279.61              1.60
Plasma magnesium, mg/dl                2.16                 2.17                  2.33               2.27               .5

    a'bMeans within rows with different superscripts differ (P<.05).

those fed c o n t r o l or NaHCO3 treatments. The
reason for this is n o t apparent.                                    The assistance o f Debbie Noel for field w o r k
     Kronfeld (13) stated that ingestion o f                     and l a b o r a t o r y analyses and o f A n n e Woelfel
excessive NaHCO3 would be e x p e c t e d to                     for sample preparation is gratefully acknowl-
induce primary m e t a b o l i c alkalosis. However,             edged, as is the assistance of n u m e r o u s student
o u r resuhs indicate no effects due to t r e a t m e n t        workers involved in the e x e c u t i o n o f this study.
on any b l o o d parameter, e x c e p t for variable             The statistical advice f r o m C. E. Gates was
differences in base excess and h e m a t o c r i t ,             valued. Manuscript preparation by Sharon
which are n o t easily explained (Table 8).                      Whitley, Diana Swanger, and Barbara Perkins is
Several studies indicated no impact o f dietary                  appreciated. Milk analyses were run through the
NaHCO3 on b l o o d pH, pCO2, pO2, o r b i c a r b o n -         c o u r t e s y o f the Texas Dairy Herd I m p r o v e m e n t
ate (21, 26), and Schneider et al. (23) and                      Association Milk Testing L a b o r a t o r y .
Escobosa et al. (7) r e p o r t e d no adverse effects
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90                                                   WEST ET AL.

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Journal o f Dairy Science Vol. 70, No. 1, 1987