Abstract: The objective of this study was to evaluate the effect of buffering agent (NaHCO₃ and MgO) or substituting Dried Sugar Beet Pulp (DSBP) with barley on milk yield, composition of milk, some blood parameters and ruminal fermentation in cows. In the experiment, four lactating Holstein cows with similar age, lactation period and milk yield were utilized. Cows with second phase of lactation were selected. Treatments consisted of control (40% Barley), control+1% NaHCO₃ (NaHCO₃), control+1% NaHCO₃+0,5% MgO (MgO) and barley substituted with DSBP. All diets were calculated to be isocaloric and iso-nitogeneous. The experiment was a 4x4 Latin square design. While milk yield was significantly higher in animals fed diets containing NaHCO₃+MgO compared with animals fed control, compositions of milk were not significantly different among the groups. Addition of NaHCO₃, NaHCO₃ + MgO significantly increased (p<0.05) acetic acid concentrations but did not affect blood parameters. In conclusion addition of NaHCO₃ or NaHCO₃ + MgO increased milk yield but did not affect composition of milk. An increase in ruminal acetic acid concentrations and acetic/propionic acid ratio due to buffering agent is an important finding. It must be revaluated the use of supplements in feeding diets since they decrease propionic acid level.

INTRODUCTION

Feedstuff production is not enough to meet the requirement in Turkey. Approximately 16-17 tons of forage dry matter are produced from pastures and ranges each year. These amounts are 20-25% of the annual forage requirement. The Southeastern Anatolia between production and need has tried to be full with creal crop residues such as straw (Saricicek and Okuyan, 1993). Thereby, in order to fulfill animal’s nutrient requirement, more concentrate feed has to be fed resulting in an increase in feed cost. Turkey is one of top sugar beet producing countries. Sugar beet by products such as wet or DSBP have high cellulose digestibility and thus are very cheap energy source for ruminant in Turkey (Deniz et al., 2001).

Ruminal pH is normally buffered by bicarbonate ions of saliva. Lowering percentage of forage in ration causes a decrease in chewing and rumination that stimulate secretion of saliva on the other hand it increases acid formation in the rumen. While concentrations of VFA increase, ruminal pH decrease as a result of rapid degradation of carbohydrate in concentrate feed in the rumen leading a significant alteration of ruminal bactria population.

Number of lactic acid bacteria thus, lactic acid production increase in the rumen resulting in acidosis (Coskun, 1998; Orskov, 1990). Sodium bicarbonate and MgO are the agents most commonly used against acidosis. These agents can be included 0.5-2.5% in diets (Coskun, 1998).

The response of animal to these agents depends on forage/concentrate ratio of diet, feed intake and amounts of buffer in diet. The aim of this study was to evaluate the effects of buffers (NaHCO₃ and MgO) and substitution of barley with DSBP on milk yield, milk composition, rumen fermentation and some blood parameters in dairy cows.

MATERIALS AND METHODS

This research was carried out in a dairy farm. Four Holstein cows with similar age, lactation period and milk yield were utilized. Cows with second phase of lactation were chosen. Chemical compositions of feed used in the experiment were analyzed as described by Weende (Akkilic and Surmen, 1979) system. Treatments consisted of control (40% Barley), control+1% NaHCO₃ (NaHCO₃), control + 1% NaHCO₃ + 0.5% MgO (MgO) and barley substituted with DSBP. All diets were calculated to be isocaloric and iso-nitogeneous (Table 1). To determine the amount of NaHCO₃ and MgO, literature values were used (Senel, 1992; Worley et al., 1986; Erdman et al., 1980, 1982).

The experiment was a 4x4 Latin square design with 15 day of initial adaptation period. The experiment consisted of 4 periods with 20 days adaptation and 7 days sampling period, a total of 27 days. Nutrient requirements of animals were determined using NRC (1988) values. Cows were milked twice a day and amounts of milk measured for each milking to determine daily milk yield during each sampling period. About 1% of milk were sampled at each milking. Then, 0.5% saturated HgCl₂ was added into milk to stop fermentation just after sampling.

Approximately 10 mL blood from V. jugularis and 100 mL rumen fluid from rumen were collected 3 h post-feeding from each animal for each period. Ruminal pH were determined immediately after sampling. Ruminal NH₃-N concentrations were determined after necessary treatments were done (Demirel and Bolat, 1996) as soon as possible. A dublicate of rumen fluid were taken into tubes (3 mL) and stored at -20°C for VFA analysis. Serum were drawn from blood and stored at -20°C for analysis.

Table 1:	Composition of concentrate feed mix used in the experiment ( %)
a: Premix provided per kg of diet: Vit A 5.000.000 IU; Vit. D3, 1.000.000 IU; Vit. E, 25.00 mg; b: Suplied (per kg of diet): Mn, 40.000.000 mg; Fe, 50.000.000 mg; Zn, 40.000.000 mg; Cu,10.000 mg; I, 500 mg; Co, 100 mg; Se, 100 mg; *: NaHCO3 and MgO were added to feed mixes after feed mix was prepared

Milk samples were analyzed for Dry Matter (DM), Crude Protein (CP), ash (Akkilic and Surmen, 1979) and fat (Kurt et al., 1993). Concentration of lactose in milk samples were calculated with an equation described by McDowell and McDaniel (1968) as follows:

While milk yields corrected for Solid Matter (SCM) were calculated according to Tyrell and Reid (1965) milk yields corrected for 4% fat (4% FCM) were calculated according to Jurgensen (1982) using following formulas:

Where:

While DM, ash, CP and Ether Extract (EE) concentrations of feedstuff were analyzed with a method described by Weende (Akkilic and Surmen, 1979), Crude Fiber (CF) contents were determined with the method of Crampton and Maynard (Akkilic and Surmen, 1979). Serum total protein, glucose levels were determined by Chema Protein (Total)^® and Chema Glucose FL (Fast)^® kits using spectrophotometry. Serum Ca, P and urea levels were analyzed by an auto analyzer. Volatile Fatty Acid (VFA) concentrations of rumen fluid were determined using HPLC. Rumen ammonia-N levels were analyzed using thedistillation unit of Kjeldahl apparatus (Deniz and Tuncer, 1995).

RESULTS AND DISCUSSION

Chemical composition of forage and concentrate feedstuff used in the experiment are shown in Table 2. Daily milk yield, composition of milk, forage intake, 3 h post-feeding ruminal pH, NH₃-N, total VFA, acetic acid, propionic acid, butyric acid, lactic acid, acetic/propionic acid ratios, serum total protein, glucose, urea, Ca and P levels are shown in Table 3. Chemical composition of forage and concentrate feedstuff used in the experiment are shown in Table 2. Chemical composition of diets were similar except diet containing DSBP. While concentrations of ash and CF were higher, concentrations of EE and NFE were less in DSBP diet compared with other diets resulted from the substitution of barley with DSBP. Because CF digestibility of DSBP is very high (Deniz et al., 2001), this difference in CF contents of diets is not very important.

Table 2:	Chemical compositions of forage and concentrate used in the experiment (%)

Table 3:	Forage intake, milk yield, composition of milk, ruminal fermentation and some blood parameters of cows
x: Total VFA consist of acetid, propionic and butiryc acids: a-cValues with different letter in the same line indicate significant difference (p<0.05)

Although, it was not statistically significant, the highest forage intake was observed in animals fed DSBP diet (Table 3).

Some researchers have indicated that DSBP increased feed intake by increasing palatability of diet (Tyrell and Reid, 1965; Jurgensen, 1982). While amount of concentrate given was fixed, animals had free access to forage in this study. Even though there was little variation among animals and periods, forage/concentrate ratio was generally 2:1.

Daily milk yiels were 10.37, 11.03, 11.44 and 10.67 kg day^-1 for control, NaHCO₃, NaHCO + MgO and DSBP diets, respectively (p<0.05). Daily milk yield was significantly higher in animals fed NaHCO₃ + MgO supplemented diet compared with animal fed control diet (p<0.05) but similar with other groups (Table 3). Solid corrected and fat corrected milk yields were similar among treatments.

Similar to the results, many studies reported an improvement in milk yield (Erdman et al., 1980; West et al., 1991; Schneider et al., 1986; Tucker et al., 1993; Rogers et al., 1985) but only one study indicated a decrease in milk yield with buffer supplementation (Aslam et al., 1991). Schneider et al. (1986) fed diets containing 38% silage, 62% concentrate supplemented with 1% NaHCO₃, 0.73 NaCI and 1.3 or 1.8% potasium to 19 kg daily milk producing cows. Addition of NaHCO₃ into diet significantly increased milk yield, fat corrected milk yield, fat content of milk. In another study, Fisher and Mackay (1983) supplemented control diet with 180 g NaHCO₃. Cows fed NaHCO₃ supplemented diet had significantly higher milk yield and fat corrected milk yield but less lactose in milk compared with cows fed control diet. Concentrations of milk fat and protein did not differ between treatments.

About 3 h post-feeding ruminal pH values were similar among treatments, ranging from 6.77-6.99. Considering the 2:1 forage/concentrate ratio of diets, these pH values are in normal range. Addition of buffers into diets increased ruminal pH when animals were fed diets low in fiber (Kilmer et al., 1981; Thomas et al., 1984).

Neither buffering agents nor source of carbohydrate did not significantly affect ruminal NH₃-N concentrations (Table 3). All ruminal NH₃-N values were above the levels (5-7 mg dL^-1) required for optimal microbial protein synthesis in the rumen (Deniz and Tuncer, 1995). Kilmer et al. (1981) have reported that dairy cows fed 0.8% NaHCO₃ supplemented diets had significantly higher `ruminal NH₃-N concentrations compared with control group. It was speculated that this increase in ruminal NH₃-N concentrations resulted from increased ruminal protein degradation due to increased pH. On the other hand, Stokes et al. (1986) fed cows with diets containing 0.7% NaHCO₃ or 0.7% NaHCO₃ + 0.28% MgSO₄ only animals fed diet supplemented with 0.7% NaHCO₃ had significantly greater ruminal NH₃-N concentrations compared with other groups. DePeters et al. (1984) have reported that supplementing control diet with NaHCO₃ above 0.25% of DM did not increase in fact decreased ruminal NH₃-N concentrations.

One of the most important finding of this study was that both NaHCO₃ and NaHCO₃ + MgO supplementations increased concentrations of acetic acid and decreased concentrations of propionic acid in the rumen. Concentrations of acetic acids were 50.26, 65.22, 62.64 and 50.38 mmo L^-1 for control, NaHCO₃, NaHCO₃ + MgO and DSBP diets, respectively (p<0.05). The concentrations of propionic acids were significantly greater in the rumen of cows fed control diet compared with those fed other diets.

These changes in concentrations of acetic and propionic acids caused by buffering agents were reflected at acetic acid/propionic acid ratios. Thus, acetic acid/propionic acid ratios were the highest in cows fed diets supplemented with buffering agents followed by DSBP (p<0.05). It has been reported that NaHCO₃ and MgO supplementation of diets increased acetic acid concentrations and decreased propionic acid concentrations via increasing rate of passage from rumen (Thomson et al., 1978; Harrison et al., 1975). Use of artificial saliva at 4 and 8% as buffering agents increased rate of liquid passage thus decreased concentration of propionic acid (Harrison et al., 1975). Similar to the results, many researchers (Erdman et al., 1980; West et al., 1987; Staples et al., 1988) have reported that buffering agents increased acetic acid, decreased propionic acid concentrations in the rumen thus caused a high acetic/propionic acid ratios in dairy cows. About 3 h post-feeding serum total protein, urea, glucose, Ca and P levels were similar among treatments (Table 3).

Serum total protein levels were 8.59, 8.83 and 8.85 g mL^-1 for NaHCO₃, NaHCO₃ + MgO and DSBP, respectively. These values were a little above the levels known as normal (6.0-8.5 g mL^-1) in the literature. However, serum total protein levels of control were in the range of normal levels (8.41 g mL^-1). Serum urea levels (6.0-36.0 mg dL^-1) were in agreement with the values reported in the literature (Altintas and Fidanci, 1993; Imren and Sahal, 1990). Even though serum glucose levels were in the range of normal levels (Altintas and Fidanci, 1993; Imren and Sahal, 1990) it was over (81.96 mg dL^-1) normal levels in animals fed diet supplemented with NaHCO₃. Serum Ca levels were 7.28, 7.58 and 6.75 mg dL^-1 for NaHCO₃+MgO, DSBP and control diets, respectively. These values were at lower edge of normal Ca levels reported for cows (Altintas and Fidanci, 1993; Imren and Sahal, 1990). However, serum Ca levels of animals fed diet supplemented with NaHCO₃ were in the range of normal values. Serum P levels were in agreement with the values reported in the literature.

Similarly, Rogers et al. (1985) have reported that 1.2% NaHCO₃ supplementation did not affect serum total protein, glucose, Ca and P levels. Addition of NaHCO₃ into diet increased serum Ca levels about 1.2 mg dL^-1 (Kilmer et al., 1980). This increase was thought to be caused by the increase in absorption of Ca in the intestine due to alteration of intestinal pH which was revealed as an increase in blood. Tucker et al. (1988) have reported that addition of 1.4% NaHCO₃ did not alter serum Ca levels. In contrast, Staples et al. (1988) noted an increase in serum Ca levels but not P levels by addition of NaHCO₃.

CONCLUSION

Addition of NaHCO₃ or NaHCO₃ + MgO increased milk yield but did not affect composition of milk. An increase in ruminal acetic acid concentrations and acetic/propionic acid ratio due to buffering agent is an important finding. It must be revaluated the use of supplements in feeding diets since they decrease propionic acid level.