EFFECT OF SUPPLEMENTAL SODIUM BICARBONATE ON NUTRIENT DIGESTIBILITIES AND RUMINAL ph MEASURED CONTINUOUSLY 1

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1 EFFECT OF SUPPLEMENTAL SODIUM BICARBONATE ON NUTRIENT DIGESTIBILITIES AND RUMINAL ph MEASURED CONTINUOUSLY 1 A. M. Kovacik, 2 S. C. Loerch 3'4 and B. A. Dehority 3 The Ohio State University 5, Wooster ABSTRACT A technique was used to monitor continuously ruminal ph using a strip-chart recording ph meter. Ruminal ph measurements were made in four ruminal-cannulated crossbred wether lambs (avg initial weight, 42.5 kg). For 1.5 h daily, lambs were given ad libitum access to 50% concentrate-50% chopped orchardgrass hay diets supplemented with O, 1.5, 3.0 and 4.5% sodium bicarbonate (NaHCO 3 ). A split-plot Latin-square design was used to evaluate NaHCO 3 level and day of adaptation on the percentage of time (%T) that ruminal ph was ~< 6.6, 6.2, 5.8, 5.4 and 5.0. No effect due to day of adaptation existed for ruminal ph measurements (P>.10), while the effect of dietary NaHCO 3 level was quadratic (P>) for the %T that ruminai ph was ~< 6.2 and 5.8, and linear (P>) for the %T that ruminai ph was ~<5.4. To evaluate the effects of NaHCO 3 on nutrient digestion, the same diets were fed to eight wether lambs (avg initial weight, 38 kg) at 85% of their ad libitum intake in a replicated 4 4 Latin-square digestion trial. Digestibilities of dry matter (DM), organic matter, N and fiber fractions were not different due to level of NaHCO 3 (P>.10). Ash digestibility increased with increasing levels of dietary NaHCO 3 (P<). Four ruminal-cannulated mature Hereford steers were also given ad libitum access to the diets in a split-plot Latin-square trial to evaluate effects of dietary NaHCO 3 level on tuminal ph and in situ digestion of soybean meal N and orchardgrass DM. During incubation of the dacron bags for 3, 6, 9, 12, 24 and 36 h, ruminal ph increased linearly (P<.05) with increasing level of NaHCO~. Soybean meal N disappearance at 3, 6, 9, 12 and 24 h of incubation and orchardgrass DM disappearance at 24 and 36 h also increased linearly with increasing level of NaHCO 3. Ruminal solid and liquid dilution rates were not affected by level of supplemental NaHCO 3 (P>. 10). The results of these trials suggest that increasing level of dietary NaHCO 3 greatly increases the proportion of time ruminal ph is above critical levels for ruminal protein and dry matter digestion, but does not affect total tract nutrient digestion when 50% concentrate diets are fed. (Key Words: Sodium Bicarbonate, Nutrient Availability, Rumen.) Introduction The net quantity of a nutrient digested in the rumen is a function of two competing rate phenomena: rate of passage and rate of digestion. Sodium bicarbonate (NaHCO3) supplementation can positively affect both of these rate phenomena. Dietary NaHCO3 has been reported to increase ruminal solid and liquid dilution rate (Harrison et al., 1976; Kellaway et t Salaries and research support provided by State and Federal Funds appropriated to the Ohio Agr. Res. and Devel. Center, The Ohio State Univ. Journal Article No Present address: Dept. of Anita. Sci., Univ. of Illinois, Urbana Dept. of Anita. Sci. 4Reprint requests: Dept. of Anim. Sci., Ohio Agr. Res. and Devel. Center, Wooster s The Ohio Agr. Res. and Devel. Center. Received April 15, Accepted September 15, al., 1978; Okeke et al., 1983a,b). Several researchers also have reported that supplemental NaHCO3 increases ruminal ph (Rogers et al., 1982; Ha et al., 1983;Okeke et al., 1983a,b). Increased ruminal ph, in turn, has been shown to increase ruminal digestion of protein (Loerch et al., 1983a; Okeke et al., 1983b) and fiber (Harrison et al., 1976; Rogers et al., 1982). A ph of about 6.0 is the critical ruminal ph below which protein digestion (Loerch et al., 1983a) and cellulolytic activity (Stewart, 1977; Russell and Dombroski, 1980) are greatly reduced. Although ruminal ph fluctuations have been measured by taking multiple samples over time (Rogers et al., 1979, 1982; Okeke et al., 1983a,b), to date, ruminal ph has not been measured continuously to quantify the proportion of time ruminal ph falls below critical levels for protein and fiber digestion. The specific objectives of this research were to determine the effects of supplemental NaHCO3 on nutrient digestion in the rumen 226 J. Anim. Sci :

2 SODIUM BICARBONATE AND NUTRIENT DIGESTIBILITIES 227 TABLE 1. DIET COMPOSITION FOR CONTINUOUS ph AND NUTRIENT DIGESTIBILITY TRIALS Level of NaHCO~, %a Item Ingredient a Orchardgrass hay, chopped (IFN ) Corn, ground (IFN ) Soybean meal (IFN ) Limestone (IFN ) Trace mineral salt b (IFN ).23.22,21.21 Selenium (200 nag Se/kg) Vitamin A (30,000 IU/g) Vitamin D (3,000 IU/g) NaHCO 3 (IFN ) Chemical composition c Dry matter Organic matter Ash Neutral detergent fiber Acid detergent fiber Crude protein % bcontains.35% Zn,.28% Mn,.175% Fe,.035% Cu,.007% I and.007% Co. CExpressed on dry-matter basis. and total tract, rate of passage, and fluctuations in ruminal ph measured continuously. Experimental Procedures Continuous ph Trial, Four crossbred ruminal-cannulated wether lambs (avg initial weight, 42.5 kg) were used to determine the effect of supplemental.nahco z on ruminal ph measured continuously. Lambs were given ad libitum access to a 50% hay-50% concentrate diet for a period of 1.5 h daily from 0830 to 1000 h. Dietary ingredients and nutrient composition are shown in table 1. Chopped orchardgrass hay, ground corn and soybean meal were the major dietary constituents and the four dietary treatments were 0, 1.5, 3.0 and 4.5% NaHCO3. The lambs were housed indoors Cole-Parmer Instrument Co., Chicago, IL. Horizon Ecology Co., Chicago, IL. in individual metabolism stalls and water was available at all times. The experimental design was a split-plot 4 4 Latin square, with days of adaptation as whole plots and effects of buffer level as subplots. Each period was 12 d. On d 4, 8 and 12 of adaptation to a new dietary level of NaHCO3 a ph electrode 6 was inserted into the rumen at 0800 h and maintained there for a 24-h period. Before daily insertion, the ph electrode was cleaned by washing in dilute HCI. Continuous ph measurements were made with a recording ph meter 7. Period starting dates were staggered by 1 d because only one continuous recording ph meter was available. After these data were collected and recorded in graphic form, the percentage of time ph fell below 6.6, 6.2, 5.8, 5.4 and 5.0 was calculated. These values were statistically analyzed by analysis of variance according to the procedures of Steel and Torrie (1960) to determine effects of NaHCO3 level and days of dietary adaptation.

3 228 KOVACIK ET AL. Digestion Trial Eight wether Iambs (avg initial weight, 38 kg) were used to determine effects of supplemental NaHCO3 on nutrient digestion. Animals were housed in individual stainless steel digestion stalls for the total collection of feces and urine. Diets were those used for the continuous ph trial (table 1). Lambs were fed once daily and water was available continuously. The experimental design was a 4 4 Latin square, replicated twice. Each period was 21 d. Days one through eleven of each period served as an adaptation phase. During adaptation, each lamb was fed 10% above its previous day's ad libitum intake. On d 12 through 21, feed offered was reduced to 85% ad libitum consumption to reduce the incidence of orts and assure uniform consumption of dietary constituents. Feces, urine and orts were measured on d 16 through 21. A 5% (by volume)aliquot of daily urinary excretion was composited by lamb and period and stored under refrigeration for analysis. Fifty milliliters of 6N HCI were added to urine buckets daily to prevent N loss by volatilization. A 10% (by weight) aliquot of daily feces was composited by lamb and period and frozen until analysis. Samples of feed, orts, urine and feces were analyzed to determine actual composition of feed consumed and the digestibilities of feed fractions. Acid detergent fiber, (ADF), neutral detergent fiber (NDF), dry matter (DM), organic matter (OM) and ash were determined by methods of Van Soest and Robertson (1980). Nitrogen was determined by Kjeldahl (AOAC, 1980) and cellulose was determined by the method of Crampton and Maynard (1938). Statistical analysis of the data was by analysis of variance according to the procedures of Steel and Torrie (1960). Treatment means were separated using Duncan's New Multiple Range Test. In Situ Digestion Trial. Four mature ruminalcannulated Hereford steers were used in a split-plot 4 4 Lafin~square experiment to determine effects of O, 1.5, 3.0 and 4.5% dietary NaHCO3 on the ruminal environment and in situ digestion of soybean meal N and orchardgrass DM. Steers were fed experimental diets (table 2) one time daily at ad libitum intake. Each period was 14 d with d 1 through 10 serving as an adaptation phase. Immediately s Instrumentation Laboratory Model 951. before feeding on d 11, 30 g of chromic oxide (Cr 203) mixed with 270 g of ground corn and 150 g of polyethylene glycol (PEG; molecular weight = 4,000) dissolved in 300 ml of water were infused as a pulse dose into the rumen. Fifty-milliliter samples of ruminal fluid were taken at 1, 8 and 24 h post-infusion for analysis of PEG according to the procedures of Hyden (1961). Fifty-milliliter samples of whole ruminal contents were taken at 1, 24 and 48 h post-infusion and prepared for Cr analysis by the procedure of Williams et al. (1962). Samples were analyzed for Cr on an atomic absorption spectrophotometer using a nitrous oxide head s. Wavelength was set at nm and band width at 1.0 nm.the slope of the regression line of declining PEG and Cr concentration over time was calculated to determine ruminal fluid and solid dilution rates, respectively. In situ soybean meal N disappearance and orchardgrass DM disappearance were determined on d 13 and 14. Immediately before feeding on d 13, 15 dacron bags (8 x 14 cm, pore size = 70/am) containing.7 g soybean meal and nine dacron bags containing 2 g of chopped orchardgrass were attached to 250-g weights and inserted into the rumen. Triplicate soybean meal-containing bags were removed after 3, 6, 9, 12 and 24 h of incubation and triplicate orchardgrass-containing bags were removed after 12, 24 and 36 h of incubation. After retrieval, bags were rinsed with cold tap water and dried at 55 C. Soybean meal N disappearance was determined by Kjeldahl and orchardgrass DM disappearance was determined gravimetrically. Rates of disappearance were determined as the slope of the regression of In residual N (3 to 12 h of incubation) or DM (12 to 36 h of incubation) over time. Ruminal ph was measured each time bags were retrieved. Data were analyzed by analysis of variance procedures with treatment degrees of freedom partitioned to test for linear and quadratic effects (Steel and Torrie, 1960). Results and Discussion Continuous ph Trial. No effect due to day of dietary adaptation or interaction of day of dietary adaptation NaHCO3 level existed (P>.10), for percentage of time (%T) that ruminal ph fell below 6.6, 6.2, 5.8, 5.4 and 5.0. Increasing levels of dietary NaHCO 3 resulted in a quadratic decrease in %T that ruminal ph was ~ 6.2 and 5.8 and linear decrease (P<) in %T ruminal ph was ~ 5.4

4 SODIUM BICARBONATE AND NUTRIENT DIGESTIBILITIES 229 TABLE 2. DIET COMPOSITION FOR IN SITU DIGESTION TRIAL Ingredient Level of NaHCO3, %a % Corn cobs, ground (IFN ) 50.0 Corn, ground (IFN ) 35.6 Soybean meal (IFN ) 13.7 Limestone (IFN ).38 Trace mineral salt b (IFN ).23 Selenium (200 nag Se/kg).07 Vitamin A (30,000 IU/g) Vitamin D (3,000 IU/g) NaHCO~ (IFN ) O bcontains.35% Zn,.28% Mn,.175% Fe,.035% Cu,.007% I and.007% Co. (table 3). Averaged over day of adaptation, %T that ruminal ph was < 6.2, 5.8 and 5.4 was 1.6-, 4.5- and fold greater, respectively, for sheep fed 0% NaHCO 3 than those fed 4.5% NaHCO 3. Fluctuations in ruminal ph measured continuously are presented in figure 1. The pka 1 of bicarbonate in ruminal contents is 6.1 (Kronfeld, 1976), thus its greatest effectiveness as a buffer would be expected at or below this ph. Supporting the report of Kronfeld (1976), increasing NaHCO3 level did not significantly affect %T ruminal ph was greater than 6.2 in our study. Ruminal ph rarely fell below 5 for sheep fed these diets; therefore, no effect (P>.10)of NaHCO 3 level existed for %T that ruminal ph was ~ 5. Many researchers have reported effects of supplemental buffers on ruminal ph during various stages of the fermentation process. In an attempt to determine buffer effectiveness during the period of most active fermentation, Stanley et al. (1972) and Russell et al. (1980) measured ruminal ph within 4 h after feeding. In contrast, Erdman et al. (1980) and Ha et al. (1983) measured ruminal ph to elucidate acid neutralization response to buffers after this initial postprandial fermentation had slackened. Other researchers have attempted to quantitate ph fluctuations throughout the postprandial period by taking multiple measurements over time (Rogers et al., 1979, 1982; Okeke et al., 1983a,b). The continuous ph measurement TABLE 3. EFFECT OF DIETARY SODIUM BICARBONATE (NaHCO 3 ) LEVEL ON RUMINAL ph MEASURED CONTINUOUSLY Ruminal ph 0 Level of NaHCO 3, %a SE b < < < < < % of 24 h cd cd c bstandard error of the mean. CEffeet of NaHCO s level was linear (P<.O1). deffect of NaHCO s level was quadratic (P<.O1).

5 230 KOVACIK ET AL. 0% Level of Sodium Bicarbonate 1.5% 3.0% 4.5% o 7.0 T c <6.0 2~ &5 5._0nl, HOURS POST-FEEDING Figure 1. Main effect of dietary sodium bicarbonate on ruminal ph technique used in this study has the advantage of being able to quantify ph fluctuations over prolonged periods of time. A similar attempt to measure ph continuously was previously described by Johnson and Sutton (1968). The continuous ph technique allows determination of important characteristics of the fermentation process such as time after feeding that ph reaches its lowest value, time required for buffers to raise ph to prefeeding values and proportion of time ph is below critical levels. For instance, it has been demonstrated that protein digestion (Loerch et al., 1983a) and cellulolytic activity (Stewart, 1977; Russell and Dombrowski, 1980) are greatly reduced when ph is below 6.0. In the present study, using the continuous ph technique, %T that luminal ph was ~ 5.8 and 69.8 and 15.4 for 0 and 4.5% NaHCO 3 diets, respectively. Thus, one would expect ruminal digestion of protein and cellulose to be greater with 4.5% dietary NaHCO3 than with 0% dietary NaHCO3, provided rate of passage is not substantially increased with buffer additions. Lamb Digestion Trial. Effects of supplemental dietary NaHCO3 levels on lamb digestion of various feed nutrient components are shown in table 4. There was no effect due to treatment on dry matter intake (DMI), or digestibility of DM and OM. These results agree with Nicholson et al. (1962, 1963) who reported that 3.1 to 5.7% NaHCO3 had no effect on DM digestibility (DMD) or OM digestibility (OMD) of all concentrate diets. However, Rogers et al. (1982) reported significant increases in both DMD and OMD when a 25% corn silage-75% concentrate diet was supplemented with 2% NaHCO3. Increased OMD was also reported by Ha et al. (1983) with lambs well adapted to concentrate diets contaning 2% NaHCO3. It is difficult to draw conclusions on effects of dietary NaHCO3 treatment on DMD and OMD because of the wide compositional

6 SODIUM BICARBONATE AND NUTRIENT DIGESTIBILITIES 231 TABLE 4. EFFECT OF SODIUM BICARBONATE (NaHCO 3) LEVEL ON NUTRIENT DIGESTIBILITY : : ', ,.,, Level of NaHCO 3, %a Item b SE c DM intake, g/d 1,127 1,113 1,161 1, DM digestion, % Ash digestion, % d OM digestion, % NDF digestion, % ADF digestion, % Hemiceilulose digestion, % Cellulose digestion, % N intake, g/d N digested, g/d N digestion, % N retained, g/d N retained, % of N digested bdm = dry matter, OM = organic matter, NDF = neutral detergent fiber, ADF = acid detergent fiber. CStandard error of the mean. deflect of NaHCO 3 level was linear (P<.O1). differences of diets in the experiments cited. While buffer treatment may improve digestibility of one component, others may be affected adversely. Because of the negative effects of low ruminal ph on digestion, ruminants fed high-concentrate diets may be more responsive to NaHCO3 additions than those fed diets containing greater amounts of forages. In our trial, where 50% forage diets were fed, the only dietary component affected by NaHCO 3 level was ash. This presumably was due to the nearly complete digestibility of ash added as NaHCO3. Similar effects of dietary NaHCO 3 on ash digestibility were noted by Nicholson et al. (1962, 1963). The NDF digestibility (NDFD), ADF digestibility (ADFD), hemicellulose digestibility (HEMD), and cellulose digestibility (CELD) were not affected by treatment (table 4). Lassiter and Cook (1963) found that steers fed water containing.5% NaHCO3 had no increase in fiber digesting capabilities over steers fed plain water. Lambs fed the same diet, however, had significant increases in crude fiber digestion when the.5% NaHCO3 solution was offered. Rogers et al. (1982) found trends toward increased ADF and NDF digestibilities when dairy cows had their diets supplemented with 2% NaHCO3. Trends toward increased crude fiber digestion were also reported by Ha et al. (1983) when 2% NaHCO3 was added to all concentrate diets fed to lambs, although little of the diet was fiber. Consistent increases in fiber digestion do not occur with dietary NaHCO 3 supplementation, even though ruminal ph can be increased (as reported in the continuous ph trial) and higher ruminal ph is known to benefit fiber digestion (Mertens, 1978). This may be due, in part, to the effects of NaHCO3 on other ruminal characteristics that are detrimental to fiber digestion such as increased rate of passage. In addition, compensatory digestion in the lower gut, as reported by Lewis (1983) may negate any differences in digestion occuring in the tureen. No differences due to NaHCO 3 level were noted for any of the N digestion measurements (table 4). Nicholson et al. (1962, 1963) reported that N digestion and N retention were not affected by % dietary NaHCO 3 supplementation. Lassiter and Cook (1963) also found no difference in N digestion when NaHCO 3 was added to drinking water of steers and lambs. Rogers et al. (1982) fed cows a 25% corn-silage-75% concentrate diet and reported that supplementing this diet with 2% NaHCO 3 had no effect on digestibility of crude protein. Ha et al. (1983) also noted no effect of 2% NaHCOz supplementation on crude protein digestion in all concentrate diets. In Situ Digestion Trial. Effects of supplemental NaHCO3 on ruminal characteristics and in situ disappearance of soybean meal N

7 232 KOVACIK ET AL. and orchardgrass DM are presented in table 5. Increasing dietary NaHCO 3 resulted in linear increases in ruminal ph at 3, 6, 9, 12 and 36 h and linear and quadratic increases in ruminal ph at 24 h postfeeding (P<). This supports the data from the continuous ph trial. There was no interaction of NaHCO 3 level and time postfeeding for ruminal ph, indicating NaHCO3 increased ruminal ph uniformly throughout the postprandial period. Ruminal liquid and solid dilution rates were unaffected by increasing NaHCOa level. Although many researchers have reported increased ruminal liquid dilution rates with dietary buffer additions (Kellaway et al., 1978; Okeke et al., 1983a,b), this increase has not always been large (Haaland and Tyrrell, 1982). Few reports of NaHCOa effects on ruminalsolids dilution rate are evident in the literature. However, Okeke et al. (1983a,b) reported increased rate of passage of Cr-mordanted soybean meal with increasing level of supplemental NaHCO 3. In contrast, Kellaway et al. (1978) reported no increases in passage of OM or ADF out of the rumen with 4.2 and 6.0% supplemental NaHCOn. Increased rate of ruminal DM digestion may have masked effects of NaHCO 3 on rate of passage in these studies. In situ soybean meal N disappearance increased linearly with increasing level of NaHCO3 after 3, 6, 9, 12 and 24 h of incubation. In situ soybean meal N disappearance was positively associated with ruminal ph. Although it was not possible in this trial to determine if this effect was due to increased solubility or increased microbial proteolysis, soybean meal N solubility has been shown to be greatly affected by solvent ph (Loerch et al., 1983a). Loerch et al. (1983b) reported that in situ N disappearance at 12 h was highly correlated with in vivo estimates of ruminal protein escape. In the present trial, soybean meal N TABLE 5. EFFECTS OF SODIUM BICARBONATE (NaHCO 3 ) LEVEL ON RUMINAL CHARACTERISTICS AND IN SITU SOYBEAN MEAL NITROGEN AND ORCHARDGRASS DRY MATTER DISAPPEARANCE Level of NaHCO3, %a Item O SE b Ruminal ph 3 h c 6 h c 9 h c 12 h c 24 h cd 36 h c Ruminal liquid dilution rate, %/h Ruminal solid dilution rate, %/h Soybean meal N disappearance, % 3 h c 6 h c 9 h c 12 h e 24 h e Rate (3 to 12 h), %/h Orchardgrass DM disappearance, % 12 h h c 36 h c Rate (12 to 36 h), %/h e bstandard error of the mean. CEffect of NaHCO 3 level was linear (P<.05). deflect of NaHCO 3 level was quadratic (P<.05). eeffect of NaHCO 3 level was linear (P<.IO).

8 SODIUM BICARBONATE AND NUTRIENT DIGESTIBILITIES 233 disappearance at 12 h was 7, 49 and 58% greater, respectively, for steers fed 1.5, 3.0 and 4.5% NaHCO 3 compared with steers fed 0% NaHCO3. There was a nonsignificant trend for greater rates of N disappearance (from 3 to 12 h) for steers fed 3.0 and 4.5% NaHCOa compared with those fed 0% NaHCO 3. In situ orchardgrass DM disappearance at 24 and 36 h of incubation and rate of orchardgrass DM disappearance (from 12 to 36 h) also increased linearly with increasing level of dietary NaHCO3. It is likely that these increases are mediated through the effects of higher ruminal ph observed with supplemental NaHCO 3 (Harrison et al., 1976; Mertens, 1978; Loerch et al., 1983a). In summary, a technique was developed to measure continuously ruminal ph. The proportion of time that ruminal ph fell below critical levels for fiber and protein digestion was greatly affected by level of dietary NaHCO3 Supplemental NaHCO 3 increased ruminal digestion of soybean meal N and orchardgrass DM, and did not affect rate of passage of solids out of the rumen. With the exception of ash, total tract nutrient digestibilities were unaffected by level of NaHC03 fed to Iambs. This may have been due to compensatory nutrient digestion postruminally. Literature Cited AOAC Official Methods of Analysis (12th Ed.). Association of Official Analytical Chemists, Washington, DC. Crampton, E. W. and L. A. Maynard The relation of cellulose and lignin content to the nutritive value of animal feeds. J. Nutr. 15:383. Erdman, R. A., R. L. Botts, R. W. Hemken and L. S. Bull Effect of dietary NaHCO a and MgO on production and physiology in early lactation. J. Dairy Sci. 63:923. Ha, J. K., R. J. Emerick and L. B. 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9 234 KOVACIK ET AL. stone additions to high grain diets on feedlot performance and ruminal and fecal parameters in finishing steers. J. Anita. Sci. 51:996. Stanley, R. W., N. Kanjanipibul, K. Morita and S. M. lshizaki Effect of feeding buffered concentrate rations on performance and metabolism of lactating dairy cattle in a subtropical environment. J. Dairy Sci, 55:959. Steel, R. G. D. and J. H. Torrie Principles and Procedures of Statistics. McGraw-Hill Book Co., New York. Stewart, C. S Factors affecting the cellulolytic activity of tureen contents. Appl. Environ. Microbiol. 33:497. Van Soest, P. J. and J. B. Robertson Systems of analysis for evaluating fibrous feed. In: W. J. Pidgen, C. C. Baleh and M. Graham (Ed.) Standardization of Analytical Methodology for Feeds. pp Int. Dev. Res. Center, Ottawa, Canada. Williams, C. H., D. J. David and O. Iismaa The determination of chromic oxide in fecal samples by atomic absorption. J. Agr. Sci. (Camb.) 59:381.