ROLE OF RUMINAL BUFFERS IN DAIRY RATION
by-DR. RAJESH KUMAR SINGH, (LIVESTOCK & POULTRY CONSULTANT), JAMSHEDPUR, JHARKHAND,INDIA 9431309542, rajeshsinghvet@gmail.com
What is a Buffer?
Buffers in dairy rations are compounds that neutralize excess acid within the animal’s digestive system. They supplement the cow’s natural buffers that occur in saliva and increase her ability to overcome the harmful effects of too much acid production.
Technically, buffers and alkalizers differ. A buffer maintains the acidity level, or pH, within a narrow range when either an acid or a base is added. Examples of commonly used buffers are sodium bicarbonate and sodium sesquicarbonate. An alkalizer raises the pH in direct proportion to the amount added. Magnesium oxide and magnesium hydroxide are good examples of an alkalizer. Both buffers and alkalizers are important for neutralizing excess acidity and both are called buffers in common usage.
Buffers are compounds which in aqueous solution help resist changes in rumen pH when high grain, low forage, fine-chopped and fermented forage (silage) are fed. Requirements for buffering agents in dairy cow diets are a function of salivary buffer secretion, feedstuff buffering capacity, acid-producing potential of the diet and feed acidity. Buffers are used largely to reduce the effect of acidic conditions produced by the relatively high grain rations fed to dairy cows. Dietary buffers have been very well researched and are widely used in the dairy industry. The term buffers is loosely applied to several compounds, including bicarbonates, carbonates, hydroxides, and oxides. The cow has three primary means of buffering acid ingested (from silage) or acid produced by rumen fermentation. These include: • buffer naturally occurring in saliva, • buffering capacity of ingested feed, and; • added dietary buffers.
Buffers in dairy rations are the compounds that neutralize the excess acid within the animal’s digestive system. A buffer is the one that maintains the pH, within a narrow range when either an acid or a base is added. The dairy animals have natural buffering system in their saliva and increase the animal’s ability to overcome the effects of higher acid production. One should first distinguish the difference between an alkalizer and a buffer. Buffer is the one which maintains a constant level of pH irrespective of the amount added; whereas an alkalizer increases the pH according to the amount added.
Buffering ability of animals —————
Cows produce 10 to 32 L of saliva per kg of feed dry matter (DM) with an average of 18.2 L/kg DM. The production of saliva is much higher when roughage is consumed than when grains are consumed. Factors that are important in saliva secretion are the dry matter content of the feed, forage intake, and forage particle size. The saliva produced by cattle, contains 125 milliequivalents (meq)/L bicarbonate and has a pH of 8.4. Rumen pH ranges from 5.5 to 7.0 and, therefore, the buffering effect of saliva becomes very important in maintaining a desirable rumen pH. The fermentation of grain by rumen microorganism results in acid production, and silage contributes preformed acid in the rumen. This acid must be neutralized or buffered by cows via their saliva to maintain rumen pH within 5.5 to 7.0. Cows fed 20 kg of dry matter can produce the equivalent of 3418 to 3617 g/d sodium bicarbonate in their saliva, depending on the level of forage in the diet (table 1). Thus, forage intake plays an important role in amount of buffer required by the animal. If a cow is fed a diet with a 70:30 grain to forage ratio, the diet would have to be supplemented with about 0.5% sodium bicarbonate to produce the same natural buffering capacity as a cow fed a diet with a 50:50 grain to forage ratio. Therefore, it is clear that the manner in which we feed dairy cows contributes to the need for supplemental dietary buffer.
Buffering capacity of feed —————–
Buffering capacity of forages can be defined as the degree to which forage material resists changes in pH. Forages with high buffering capacities will resist large reductions in the rumen pH. Legumes tend to have a higher buffering capacity than grass and barley silage. Since forages differ in their buffering capacities, the dietary buffer requirement of cows fed different forages would be different. Therefore, it is possible that cows fed barley silage would respond better to added buffers than cows fed alfalfa silage or hay. Protein, total ash and cation (Na, K) content of forages are good indicators of total buffering capacity. Buffering capacity increases as these measures increase.
Low fibre diets——————
Scarcity of high quality forage often results in feeding high grain diets to meet the energy requirements of lactating dairy cows. As the proportion of grain in the diet increases, rumen pH, rumen acetate:propionate ratios and milk fat percentage decreases (see article 1F2). Rumination and salivation are also reduced as a result of reduced dietary fibre intake. Reduced salivation, caused by inadequate effective fibre (long chopped forage) in the diet, may be compensated for by feeding rumen buffers to augment the natural buffering ability of cow. In diets containing low concentrations of fibre, addition of dietary buffers results in increased rumen pH. The effect of added buffers on rumen pH would be most beneficial 4 to 9 hours after initial feeding when rumen pH tends to be lowest. The suggested optimum range of pH for maximum cellulose digestion is 6.4 to 6.8. When rumen pH is at 6.5, 40% of the NDF in the diet would be digested, while at pH 5.5 digestion is less than 20%, and at pH 5 there is essentially no NDF digestion. Decreasing ADF content of the diet by one percentage unit results in a 0.0564 unit decline in rumen pH. Reduction in rumen pH in dairy cows results in a 3.6 unit decline in ADF digestion for each 0.1 pH unit decrease when rumen pH is below 6.3 and may result in depressed feed intake. Maintaining fibre level at a minimum of 19% ADF has been suggested to maintain normal rumen pH and milk fat percent. Milk fat test would increase by 0.145 percentage units if the dietary ADF increases by one percentage unit (at ADF levels above 14%). To increase the butter fat test by 0.145 percentage units, the equivalent of 108 g of bicarbonate and 54 g of magnesium oxide (Mag Ox) would need to be added to the diet.
Endogenous buffering
Ruminant animals possess complex system for buffering the organic acids produced during carbohydrates during the ruminal fermentation. While the total effect of buffering on ruminal pH is relatively small and it accounts for the margin between health and disease in dairy cows when fed large amounts of fermentable carbohydrates (Firkins, 1997). Cows produce a large amount of buffers through their saliva. Saliva buffers the ruminal pH because it is rich in sodium, potassium, bicarbonates and phosphates (Van Soest, 1994). Unfortunately, saliva secretion is not triggered by reduced ruminal pH, but rather is affected by the amount of physical fiber present in the diet. Saliva is secreted during chewing activity (both during eating and rumination being higher production) in response to the amount of physical fiber present in the diet.
Acid absorption
Rumen has the potential to absorb the organic acids rapidly once it’s formed from the rumen which is main reason behind the pH stability inside the rumen. However, the peripheral tissues rarely have the potential to utilize Volatile Fatty Acids (VFAs); however, absorption of these VFA from the rumen can be an important bottleneck. Absorption of VFA via the rumen wall occurs passively. This passive absorption rate depends on the length/number of finger-like papillae that project away from the rumen wall. The papillae increase in length when animals fed high grain diets than roughage diets; the dairy animals in dry pregnant periods are fed only with low quality roughages which causes the reduction in the papillae size and number. However, the animals after calving the farmers are feeding high concentrate diets which results in higher acid production in the rumen. But to this change in ruminal papillae the efficient absorption of VFAs is not possible which resulted in development of acidosis in newly calved animals. If the absorptive capacity of these cells is impaired it becomes more difficult for the animal to maintain a stable ruminal pH of 6.5 to 6.8.
Where is the need for a dairyman to use the ruminal Buffer?
The emphasis on increased production and efficiency in dairy cows has led to the increased use of high concentrate or in nutritional terms high energy rations than the roughage based one. These rations contain more readily fermentable starch that results in increased acid production in the rumen. As these rations are low in fibre content resulted in less chewing time, reduced production of saliva and subsequently leads to acidosis. In early lactation or high producing cattle the ruminal buffers will help make the transition from high roughage during dry period to high concentrate rations after calving since the risk of acidosis is greatest at this point of time. During the period of heat stress, there will be reduction in dry matter intake and loss of electrolytes from the body. Addition of ruminal buffers could help to restore the feed intake and replace lost electrolytes.
The Bicarbonate System
The commonly used ruminal buffer is HCO3-. The bicarbonate system includes two major ionic forms: HCO3- and CO3-. The HCO3- is of primary importance to buffering the blood of animals because it may be protonated to H2CO3. The pKa for this acid is only 3.80 at 37°C and 0.15 M ionic strength .
Added dietary buffer
Under normal feeding practices, high producing dairy animals will be fed with large amounts of grain and hence, the addition of buffers might be required to supplement natural endogenous buffer in as saliva. Low fibre diets often result in feeding high grain diets to meet the energy requirements of lactating dairy cows. As the proportion of grain in the diet increases, rumen pH and rumen acetate, acetate: propionate ratios and milk fat percentage decreases whereas proportion of propionate got increases. The process of rumination and its associated salivation also got reduced as a result when the animal has lower fibre intake. Decreased salivary secretion, caused by inadequate effective fibre (long chopped forage) in the diet, may be compensated for by feeding rumen buffers to augment the natural buffering ability of cow. In diets containing low concentrations of fibre, addition of dietary buffers results in increased rumen pH. The effect of added buffers on rumen pH would be most beneficial for about 4 to 9 hours after initial feeding when rumen pH tends to be lowest.
The suggested optimum range of pH for maximum cellulose digestion is 6.4 to 6.8. When rumen pH is at 6.5, 40% of the Neutral Detergent Fibre (NDF) in the diet would be digested, while at pH 5.5 digestion is less than 20%, and at pH 5 there is essentially no NDF digestion. Reduction in rumen pH of dairy cows will results in about 3.6 units decline in Acid detergent fibre (ADF) digestion for each 0.1 pH unit decrease when rumen pH is below 6.3 and may result in depressed feed intake. Maintaining fibre level at a minimum of 19% ADF has been suggested to maintain normal rumen pH and milk fat percent. Milk fat would increase by 0.145 % units if the dietary ADF increases by one percentage unit (at ADF levels above 14%). To increase the butter fat by 0.145 % units, the equivalent of 108 g of bicarbonate and 54 g of magnesium oxide would need to be added to the diet.
Feeding buffers to dairy animals can help to maintain intake and digestion
Feeding ruminal buffers will maximise the microbial growth and production will maintain the high milk yields, safeguard herd health and maximise profitability. Rumen microbes are essential for the digestion of forage. These rumen microbes produce volatile fatty acids and microbial protein and in doing so they can provide up to 75% of the energy and up to 60% of the amino acids required by the high yielding cow. For the rumen to work efficiently and effectively the rumen microbes need a steady supply of fermentable energy and degradable protein and most importantly they need a stable rumen pH between 6.5 and 6.8 pH. Within this pH range the rumen is at its most efficient. Researchers showed that buffer will be helpful in restoration of a depressed fat.
Why Does the Dairyman Need a Buffer?
The emphasis on increased production and efficiency in dairy cows has led to the increased use of high concentrate or high energy rations. These rations contain more readily fermentable starch which results in increased acid production in the rumen and subsequent acidosis. Also, rations with lower fiber levels result in less chewing time and reduced production of saliva with its natural buffers.
What are the Effects of Acidosis?
Too much acidity can reduce feed intake, decrease ration digestibility, lower milk production and decrease butterfat test. Excess rumen acidity also endangers cow health. Ruminal acidosis can bring on fatty liver syndrome, liver abscesses, rumenitis and laminitis. When excess acidity may be a problem, addition of a buffer is good insurance.
When Should a Supplemental Buffer be Fed?
There are several situations in which feeding a buffer supplement may give an economically favorable response and should be considered:
- High corn silage rations—These are high in moisture and soluble carbohydrates and are low in pH. These factors combined with less salivary secretion can lead to more acidity in the rumen.
- Wet rations with fermented feeds—Fermented rations depress total dry matter intake.
- Lower fiber rations—Lower fiber rations depress rumination and result in depressed feed intake and lower butterfat percentage.
- Fine chopped haylage—Results in reduced chewing time and lower fiber digestion in the rumen. Buffers can help maintain intake and digestion.
- High concentrate rations—High levels of starch can be fermented rapidly and lead to subclinical acidosis.
- Early lactation/ high production—Buffers help make the transition to high concentrate rations after calving. The risk of acidosis is greatest at this time.
- Heat stress—Heat stress can reduce dry matter intake and affect electrolyte balance. Buffers can help restore feed intake and replace lost electrolytes.
- Low fat test—Research shows that buffers help restore a depressed fat test. Fat test variation of individual cows may be concealed by a normal herd average. Watch for individuals having a protein percentage higher than the fat test.
Rumen Buffers
Limestone Flour –
Mistakenly ground limestone flour has often been recommended as a rumen buffer fed at 100gms – 200gms per cow on the grounds of price. Whilst limestone flour is an excellent source of calcium, well absorbed at the very low pH seen in the true stomach, it is in fact largely insoluble above about 5.5 pH. It is therefore totally unsuitable as a rumen buffer and should not be used as such.
Inappropriate use of ground limestone flour can also interfere with a range of other nutrients including phosphorous, zinc, copper, iodine, selenium and manganese resulting in trace element deficiency which has on occasions resulted in problems with lameness, high somatic cell counts and mastitis. When using any buffer, diets need to be checked by a competent nutritionist who can advise on mineral, trace element interactions.
Sodium Bicarbonate –
Traditionally Sodium bicarbonate (NaHCO3) has been used to buffer dairy diets. However results have been mixed. It is only effective with very low rumen pH or for neutralising low pH silages. Having said that trials have shown that bicarb does not remove lactic acid from the rumen. Also sodium bicarbonate is highly soluble and is rapidly eliminated from the rumen. Consequently bicarb works for a very limited time and is unable to provide any long term stabilising effect.
Sodium bicarbonate as with some other rumen buffers can result in very rapid rumen pH rises which can adversely affect the rumen environment. To be effective sodium bicarbonate requires a relatively high feed rate of up to 200gms – 250gms which can result in a higher cost per cow than other rumen buffers. The high sodium level in sodium bicarbonate can however, restrict its use in many diets. since feeding 250gms of sodium bicarbonate is equivalent to feeding 170gms of salt.
Recent research work has demonstrated that sodium bicarbonate increases rumen outflow rates lifting dry matter intakes but reduces rumen fermentation efficiency. The result of this is that the diet is less well digested. Cows eat more, but milk yield responses are lower than when using slow release calcareous rumen buffers such as Acid Buf or Ostrea.
Acid Buf –
Acid Buf is a natural product, derived from calcified seaweed with a very fine particle size. Acid Buf provides calcium, magnesium and a range of important trace minerals. It is normally fed at 100gms – 125gms / cow and has proven effective in reducing the acid load of wet, low pH silages as well as in raising rumen pH. Some care is needed since Acid Buf has the potential to give very rapid and large pH rises beyond the optimum range for rumen pH.
Proprietary Rumen Buffers –
There are a number of proprietary rumen buffers available in the India, produced by various mineral manufacturers. These usually contain a combination of buffer and neutralizing ingredients such as sodium bicarbonate, sodium carbonate, ground limestone, magnesium oxide, calcified seaweed and sometimes a token amount of yeast. These are designed to have a spread of ingredients which may buffer over a long time period however since they carry additional manufacturing costs are generally more costly than individual straight buffers.
Live Yeast Supplements –
Live yeast supplements work quite differently to rumen buffers. They do however remove lactic acid from the cows rumen, lift rumen pH and stimulate increased rumen digestion both improving feed efficency and lifting animal output. Live yeast and rumen buffers compliment one another.
Both are very cost effective compared with reduced feed efficiency, lost output and increased concentrate feed costs associated with not achieving optimal rumen efficieny throughout lactation. The combined cost of using a rumen buffer in addition to yeast as standard in dairy diets is less that of 0.5 litre of milk but the benefits are massive. Buffers are beneficial even at grass where the rumen can be as low as 5.4 pH. With this in mind there is good reason to include rumen buffers in all dairy diets.
The most common reasons for adding buffers to the diet are to compensate for reduced saliva secretion of cows fed inadequate amounts of forage and to neutralize excess rumen acidity resulting from fermentation of starchy grains. Ideally, buffers should be released during the interval of most severe acid production in the rumen or they should provide a continuous release to prevent sudden drops in rumen pH. Palatability is a consideration when selecting a buffer. Palatability is usually not a problem when buffers are fed in a Total Mixed Ration (TMR) or when mixed with the silage portion of the ration.
