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~ ",0 ' ~ OO ~ " OO m s o [-, r~ z .0 ~> "~ z~ s II e~ Z~ 9 mZ .,4. v V o o o o u= e4 M 7 S 8 [..., 0 + =~ .s ,m< "r' .o o o o o 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~ mm O ~m .,Q r~ O0 ~z .t2 O ~O l.a o ~N .r" e, < < 8 r~ o [.., < 0 ,/ .1 < [- . ~-i ~ . ~ ~.~~ ~ ~ ~ ~'.-, ~ 0 ~.- 0"~ "-2 t.~ ~..r~ 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. 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