Effect of feeding buffer on feed intake, milk production and rumen fermentation pattern in lactating animals: A review
The dairy industry is under great pressure to supply the required milk and dairy products. For this reason, the size and capacity of dairy farms are developing day by day and advanced technologies are used to improve their productivity and efficiency. On the other hand, researchers are faced with the challenge of maintaining milk quality in the face of increasing production. To produce more milk, it is necessary to use a higher percentage of concentrate in the diet, but using a higher percentage of concentrate in the diet can be harmful to the rumen environment and challenge the productivity of the livestock. For this purpose, researchers use various additives to prevent these undesirable effects and the creation of subacute acidosis in the rumen, among which buffers play a more prominent role. Several studies indicate that buffers not only maintain rumen homeostasis but also increase animal production and productivity. This study was conducted to investigate the effect of buffering on feed intake, milk production and rumen fermentation patterns in lactating cows.
Introduction
Nutrition is a key factor affecting the performance, health and welfare of cows. However, the quantity and quality (especially milk fat content) are strongly affected by changes in the diet. For this reason, producers consider short-term measures to align with the market and adapt to it. For example, cows with high genetic potential for milk production have less than optimal access to nutrients, including energy and protein. To combat this, farmers use highly digestible diets, usually fermentable carbohydrates, and ensure that the cow has access to the energy required for high production. High energy content can provide the energy required by the cow, but on the other hand, it leads to more severe consequences that lead to reduced productivity and ultimately reduced profitability. Since ancient times, the digestive system of ruminants has developed for forage feeds. Therefore, dairy cows fed concentrated diets (with limited amounts of effective fiber) often develop metabolic disorders. Subacute rumen acidosis (SARA) is the most common and has significant financial consequences for the dairy farmer. SARA is a major concern for dairy farmers because it is associated with various adverse effects such as reduced dry matter intake and fiber digestion. Reduced milk fat, laminitis, hepatomegaly, and even death are symptoms of SARA. Enemark et al. (2002) reviewed studies on the etiology, pathogenesis, occurrence, significance, diagnosis, and prevention of rumen acidosis with special attention to clinical subacute rumen acidosis and concluded that the metabolic acidosis produced appears to be observed in the feces. In an attempt to manage and reduce SARA, feed additives are added to the diets of dairy cows, with buffers being the most commonly used compounds. These can be provided by endogenous production (through saliva) and/or through dietary buffers, of which sodium bicarbonate is the most commonly used compound in the industry. Buffers are very effective in preventing SARA. Mineral buffers are routinely added to the diet to prevent acidosis, particularly in diets with very low fiber content. Buffers may prevent overgrowth of acid-resistant lactobacilli and also prevent a potential decrease in rumen pH. However, buffers should not routinely be used to compensate for poor nutritional management. Buffers are compounds that neutralize excess acid in the digestive system of cattle. Technically, buffers and alkalinizers are different. A buffer (e.g. sodium bicarbonate and sodium sesquicarbonate) maintains the acidity or pH level within a narrow range when an acid or a base is added, in contrast, an alkalinizer e.g. Magnesium oxide and magnesium hydroxide raise the pH in direct proportion to the amount added.
Mechanisms involved in the regulation of acid-base balance in dairy cows
The regulation of acids and bases in the body is controlled by small changes in the concentration of hydrogen ions, which may slow down or accelerate chemical reactions in cells. High concentrations of hydrogen ions lead to acidosis. To prevent acidosis, the body has defense mechanisms: acid-base buffer systems (bicarbonate buffer system), respiratory regulation, and renal excretion are among these systems. Feeding dairy cows high-concentration diets not only increases milk production, but also increases the risk of acidosis due to acid production in the rumen. There are three main systems that regulate the concentration of hydrogen ions in fluids to prevent acidosis or alkalosis: (1) The chemical acid-base system of body fluids, which immediately combines with acid or base to prevent excessive changes in hydrogen ion concentration. , (2) respiratory centers that regulate the removal of CO2 (and therefore H2CO3) from the extracellular fluid, and (3) kidneys that can excrete acidic or alkaline urine, thereby reducing the hydrogen ion concentration of the extracellular fluid toward normal. Buffers are mixtures of weak acids and their salts that help maintain the pH of the rumen. Alkalizing agents neutralize the acid and raise the pH. Buffers are used to maintain milk fat levels and feed intake in the diet, and they inhibit excessive drops in rumen pH and thus maintain the vital balance of acetic and propionic acids.
Effect of Buffers on Feed Intake in Ruminants
Since buffers have the ability to stabilize rumen acidity, cellulose digestion is more efficient and rumen turnover is increased, resulting in higher feed intake and accelerated rumen emptying. The researchers reported that diets with and without 1.5% sodium bicarbonate had no effect on production, although dry matter intake was slightly increased in buffered diets. Erdmann et al. studied digestibility parameters, where they showed an increase in apparent ADF digestibility from 36% to 45.1% and 46.8% for 1.0% NaHCO3 and 0.8% MgO, respectively. Many other studies support the findings that buffers increase dry matter intake. In contrast, Ehrlich and Davison found that cows fed 4% sodium bentonite had reduced feed intake when fed sorghum-based diets, and that apparent dry matter digestibility was reduced when 0.6 and 1.2% sodium bentonite was added to the diet. Similarly, in another study, ADF digestibility was also reduced for cows fed 1.2% sodium bentonite. Kenley et al. reported that cellulose or ADF digestibility was not altered when animals were fed sodium bicarbonate. Hassan et al. reported that dry matter intake (DMI) of lactating animals increased with increasing dietary DCAD, which resulted in higher milk production. Due to the high metabolic rate and tendency to acidify the cellular environment, positive DCAD is given to obtain better performance in lactating animals. Patton et al. found that adding sodium bicarbonate to the diet of cows did not alter the dry matter intake (DMI) of the animals. Tucker et al. reported that natural sodium sesquicarbonate fed throughout lactation increased DMI per unit metabolic body weight at 4 months postpartum. Bouguin et al. found no change in DMI in cows fed diets high in starch or fiber with or without supplementation with 1% sodium bicarbonate.
Effect of Buffers on Feed Digestibility in Ruminants
McKinnon et al. conducted an experiment to observe the effect of bicarbonate supplementation on milk production and acid-base balance in lactating cows and found that apparent digestibility of DM, CP, and ADF for cows and heifers was not significantly affected by treatment. Conley et al. reported that feeding sodium bicarbonate did not affect DM, CP, or NDF intake in cows fed high- or low-forage diets. Solorzano et al. studied the effect of sodium bicarbonate supplementation with sodium sesquicarbonate supplementation in lactating cows and observed increased nutrient intake and nutrient digestibility in both groups compared to the control group, thus indicating that sodium sesquicarbonate is as effective as sodium bicarbonate. Johnson et al. found that the addition of synthetic zeolite reduced DM and OM digestibility, but they suggested that the lower digestibility could be attributed to the intake of indigestible synthetic zeolite. Meschi et al., using a meta-analysis approach (42 diets, 40 studies), found that buffer addition at concentrations between 0.5 and 2.5% DMI did not affect DM digestibility but improved fiber digestibility.
The effect of buffering on acid-base balance in ruminant acidity
In a study conducted in 1980 by Erdman et al., it was shown that adding 1.5% sodium bicarbonate to the diet and increasing the percentage of concentrate to 60% of the diet did not cause any change in ruminal acidity. They also reported that magnesium oxide was more effective than sodium bicarbonate and provided more stability in ruminal acidity. In another similar experiment in fistulated cows, supplementation with 0.8% magnesium oxide and 1% sodium bicarbonate increased ruminal acidity to 6.03 and 6.28, respectively. In another experiment, the addition of 1.2% sodium bicarbonate or sodium sesquicarbonate caused a ruminal acidity of 5.5, which was significant compared to the control group, which was 4. Roytt and Tucker (1992) conducted an experiment to observe the effect of rumen buffers: the effects of time on the buffering capacity and pH of rumen fluid were studied in cows fed a 68:32 ratio of concentrate to sorghum silage. The rumen fluid was incubated with NaHCO3, a natural sodium sesquicarbonate, a multi-element buffer or MgO (7.1 g/l rumen fluid) or no buffer for 48 h and it was found that NaHCO3 and sodium sesquicarbonate increased both the pH and buffering of the rumen fluid. Cows also showed changes in the pH of their feces and urine when they consumed the buffer. Erdman et al. (1980) reported that supplementation of 0.8% magnesium oxide and a combination of 0.9% magnesium oxide plus 1.0% sodium bicarbonate in a diet containing 60% concentrate in early postpartum cows increased fecal pH from 5.95 to 6.44, while urine pH did not change. Ghorbani et al. (1989) reported that cows supplemented with 1.0% sodium bicarbonate showed an average increase in urine pH from 8.05 to 8.15 at 180 days postpartum. They also showed that urine pH continued to decrease approximately 2 and 4 hours after feeding the buffered and control diets, respectively. Cows fed the unbuffered diet also had a decreased urine pH. Ruminants excrete alkaline urine except when fed high-concentrate diets. Most of the acid in urine is in the form of the NH4+ ion, which helps lower the pH.
Blood Acidity and Respiratory Gases
Blood pH is critical for animal survival with lethal levels outside the range of 7.0-7.8. Normal pH is 7.4. The respiratory system’s job to provide sufficient CO2 to maintain a constant blood pH under severe conditions has made it difficult for many researchers to detect pH differences. In a study by Schneider et al. (1986), cows exposed to heat stress experienced blood alkalosis at a pH of 7.44, likely due to hyperventilation and decreased CO2 pressure. The difference was statistically significant compared to the normal level of 7.40. However, the difference was only 0.04 units. A study by Begner et al. (1997) reported that sodium bicarbonate and sodium propionate were equally effective in increasing blood bicarbonate concentration and blood pH to 7.4 in acidotic dairy cows. Salt-containing diets were also ineffective in correcting acidosis with a blood pH of 7.34. McKinnon et al. (1990) found that buffer supplementation increased blood pH in cows compared to a control diet containing NH4Cl, but not in heifers. Sulzberger et al. (2016) found that dietary clay supplementation (acting as a buffer) did not significantly alter blood gas parameters in Holstein cows after grain size treatment, but significantly (P≤0.001) altered rumen pH, fecal pH, base excess, and blood HCO3-, and blood pH. Hu et al. (2007) found that the relationships between feed intake and acid-base status of lactating cows can be manipulated by dietary cation-anion difference (DCAD). Blood gas analysis is a valuable tool for diagnosing acidosis in dairy animals because it provides a good assessment of acidosis while being less invasive than rumen pH analysis.
Effect of Buffers on Ruminant Fermentation
Mao et al. (2017) conducted an experiment to observe the effect of sodium bicarbonate buffer supplementation (70 mg/1000 mg substrate) (with a ratio of concentrate to forage; 70:30) on ruminal fermentation, lipopolysaccharide and biogenic amine levels, and ruminal microbiota composition in vitro. They reported that the bicarbonate group had higher pH, total gas production, and total VFA concentration. There were higher proportions of acetate, propionate, valerate, and total branched-chain VFA, and lower proportions of butyrate. Bouguin et al. (2018) studied the effect of sodium bicarbonate supplementation (1%) in lactating cows fed high-starch (23.1%) or low-starch (5.9%) diets. They observed an increase in ruminal pH with increasing sodium bicarbonate, However, no effect was observed on methane emission and other rumen characteristics such as total VFA and protozoa. Kavas et al. (2007) reported that adding bicarbonate to lamb diets could increase rumen VFA concentration and shift their molar ratio to a higher ratio of acetate, which was in support of the findings of Coppock (1982) in lactating cows. Ghorbani et al. (1989) compared the effect of 1% sodium bicarbonate supplementation with sodium sesquicarbonate on rumen fermentation and acid-base balance in lactating cows. They found no difference in the mean molar percentage of isobutyrate, isovalerate or total VFA. Sesquicarbonate supplementation in lactating animals increased the molar percentage of acetate and decreased the molar percentage of propionate, resulting in a higher acetate to propionate ratio compared to cows fed sodium bicarbonate.
Effect of Buffers on Milk Production and Milk Composition
Rindsig et al. (1969) studied the effects of sodium bentonite at 5 or 10% of pelleted concentrate for cows fed reduced milk fat diets and found that milk production was significantly increased only at the 5% level. In contrast, Fisher and Mackey (1983) compared the feeding of sodium bicarbonate and sodium bentonite. There was a decreasing trend in dry matter digestibility and milk production with the addition of sodium bentonite, but the differences with the control diet were not significant. Erdmann et al. (1980) observed increased production when 0.8% manganese oxide and 1.5% sodium bicarbonate were fed in combination in a 60% concentrate diet. Schneider et al. (1986) also reported increased production for cows fed 1.0% sodium bicarbonate compared to cows fed salt or potassium chloride. Ecker et al. (1994) reported similar milk production throughout lactation from cows fed natural sodium bicarbonate sesquihydrate and control cows, and the shape of the lactation curves was similar to the control. Buff acid (skeletal remains of the seaweed Lithothamnium calcerium) is another buffer that is effective when added to acidic dairy diets. Kruiwagen et al. (2004) reported that inclusion of 0.3% of the diet dry matter (or 80 g/day) of buff acid was sufficient to optimize milk production and feed efficiency in milk. In another study, Kruiwagen et al. (2007) compared buff acid with sodium bicarbonate for their effects on milk production and composition. They reported that the Acid Buf treatment resulted in significantly higher daily milk production of 31.6 liters per cow, compared to 27.6 and 29.1 liters per cow for the control and sodium bicarbonate treatments, respectively. They also reported higher milk fat content for the Acid Buf treatment (42.1 g/kg) compared to the control (38.6 g/kg) and sodium bicarbonate (41.8 g/kg) treatments. Clark et al. (2009) in a study evaluating the effects of sodium carbonate sequivate in dairy cows showed that cows fed a diet containing 1% sodium carbonate sequivate had significantly increased milk production, 4% fat-modified milk, fat, protein and non-fat solids compared to the control cows.
Milk Fat
The main reasons for feeding buffers are to prevent milk fat loss by increasing its amount and to encourage feed intake. High-concentrate diets favor a rumen environment that supports the production of propionate rather than acetate. Rindsig et al. (1969) observed that cows supplemented with sodium bentonite at concentrations of 5 and 10% of pelleted concentrate increased acetate and decreased propionate in the rumen. Esdiel and Sutter (1972) found that cows fed 9–12 mol of sodium bicarbonate continuously increased their acetate to propionate ratio from 1.1 to 2.8. Logically, if acetate levels increased, milk fat would increase. Some studies do not support this theory. Rearte et al. (1984) reported that supplementation of 1.9% sodium bicarbonate to lactating Holstein cows on rotational grazing did not alter milk fat or VFA ratio. On the other hand, Erdman et al. (1982) [22] reported that many studies have shown that milk fat increases when cows are fed buffers. Similarly, it has been shown that the acetate to propionate (A:P) ratio can be increased by buffer supplementation. Kenley et al. (1999) found that cows fed a 75% concentrate diet supplemented with sodium bicarbonate increased their A:P from 1.31 to 2.0. The differences in the different studies could be due to environmental, physiological, genetic, and feed type situations. For example, Danker and Marx (1980) found no change in milk fat percentage even when cows had increased milk production, feed intake, and weight gain compared to control cows. In this case, the priorities for fat utilization could be shifted towards tissues rather than milk production. Perhaps the physical condition of the cow was favorable in some cases, as buffer supplementation in the lactating animal increased acetate, while milk fat levels remained unchanged.
Milk protein
Tucker et al. (1994) reported an increase in milk protein when sodium bicarbonate was given to cows during mid- and late lactation (9–44 weeks). However, other studies reported no change. Tucker et al. (1994) used natural sodium sesquicarbonate for the entire lactation period in dairy cows and observed that milk protein content was 0.09 units higher for naturally occurring sodium sesquicarbonate during lactation. This difference did not appear in mid-lactation and was more pronounced in late lactation. The effect of dietary buffers on milk protein content is not as well defined as the effect on milk fat content.
Conclusion
Buffer supplementation in high-producing lactating animals maintains rumen homeostasis by resisting any changes in pH. Buffer supplementation tends to increase rumen acetate:propionate ratio and fiber digestibility, thereby increasing fat percentage and milk production. Buffers also tend to increase dry matter intake in animals, which helps maintain high productivity in lactating animals. Therefore, buffer supplementation may serve as an effective and economical tool for dairy farmers to meet the increasing demand for milk and milk products.
