Dairy Cows must have a healthy rumen environment in order to achieve maximal milk production and for good health. When the rumen environment becomes impaired feed digestion is weakened and a number of metabolic diseases may occur. The rumen microbial population is the central component of the rumen ecosystem. The rumen is essentially a fermentation chamber, where pH is the central issue to a healthy flow in microbial population, stable for fiber and feed intake to be digested at a maximal rate with a pH range from 6.2 to 6.8. When the rumen pH falls below 6, fiber digestion diminishes and dry matter intake declines from a considerable loss in endogenous enzyme functionality and a drop in microbial yield and effectiveness.

 

Modern dairy cows increase the challenges to maintain rumen pH. Relatively high grain rations are fed today for various reasons. The modern dairy cow is genetically superior for its capability to maintain levels of high production and performance cost effectively by elevated nutrient density through increased grain proportions providing necessary energy. However, a consistent reliance upon finely chopped, fermented feeds, and increased grains, retards rumen fermentation by decreased pH.

 

Buffers and alkalis are compounds, which in aqueous solution help resist changes in rumen pH or increase pH when high, grain, restricted roughage or low forage, fine-chopped and fermented forage (silage) are fed. Feeding high grain, restricted- roughage diets without buffering supplements can lead to acidosis or less severe disorders as depressed milk fat and reduced starch digestibility.

Buffers help to promote thriving rumen micro flora and fermentation, by resisting changes and maintaining optimal rumen pH. In addition research shows buffers’ minimizing wide fluctuations in rumen pH improves fiber digestion, VFA- acetate: propionate ratio for enhanced DMI, milk fat percentage and overall milk yield. Published experiments documented that the use of sodium bicarbonate, sodium sesquicarbonate, magnesium oxide, calcium magnesium carbonate and other mineral supplements are effective buffering and/or alkaline agents.

 

Requirements for buffering supplements in dairy cow diets are a function of salivary buffer secretion, feedstuff buffering capacity, acid-producing potential of the diet and feed acidity. Dietary buffers are widely used in the dairy industry; still much more research is necessary.

 

Preliminary measurements were conducted to ascertain the efficacy of dietary supplements (buffer/alkaline) on rumen fermentation by measuring pH and gas production in vitro rumen fluid over time to 24h. Reactivity of similar supplements was conducted at another outside laboratory as initial measurements of mineral buffer/alkaline reactions. Gas production technique is an effective method to predict rumen fermentation model in vitro since it also correlates linear relations with VFA and NDF patterns and the fermentative digestion of feed or rations in the rumen. Previous research shows that supplementation of sodium bicarbonate in the ration contributes to well-managed herds with flourishing rumen microbe populations, increased milk fat and yield.

 

Reactivity of supplements sodium bicarbonate (BC) magnesium oxide (MgO), a magnesium carbonate / magnesium oxide blend (MgO/MgCO3), and two granular (A & B) from different suppliers and one fine grade dolomitic limestone, A (CaMgCO3) were quantified by the solubility of the major salts produced during the reaction, altering the reaction mechanism and speed of neutralization. The reactivity was measured by reacting material with 1.0N acetic acid maintaining a neutralized pH of 6.8 and calculated on ratio of change in time (Figure 1).

 

Total Acid Consuming capacity (TACC) was determined for sodium bicarbonate (BC), two sodium sesquicarbonates (SSC & SSCII), magnesium oxide (MgO), a magnesium carbonate/magnesium oxide blend (MgO/MgCO3), and a calcium magnesium carbonate (CaMgCO3) dolomitic limestone, fines A. TACC was calculated as meq/g of supplement (Table 2).

 

Ruminal fluid was collected from cows consuming an early lactation high grain diet. Fluid was incubated for 24h with an early lactation diet (Table 1) and enough supplements to provide equal meq TACC. The ability of supplements to alter rumen fermentation pH was measured essentially as described by Schaefer et al. (1982), but using medium described by Carriquiry et al. (2008). The ability of supplements to alter rumen gas production during the incubation was measured as described by Menk and Steingass (1988) and Chenost et al (2001).

 

 

Both BC and MgCO3 had the greatest rates of reaction in acid titration to maintain a neutralized pH of 6.8, similar to the optimal pH in rumen (Figure 1). 

 

The TACC of each supplements differed from the others except the two-sesquicarbonate supplements (Table 2).

Fermentation pH. Effects of most supplements were evident within the first hours up to six hours of incubation. A greater pH was maintained by BC than any other supplement (Figure 2, Table 3). Incubation pH of CaMgCO3 fines, A did not differ from the un-supplemented (blank) incubation.

Gas Production: Effects were evident within the first 5h of incubation (Figure 3) and differences among the supplements were very similar to the differences in incubation pH (Table 3). Incubations that maintained a greater pH produced more gas. Incubations with sodium bicarbonate produced more gas than those with other supplements.

 

 

 

These preliminary measurements indicate sodium bicarbonate- the standard buffer, had the greatest effect on rumen fermentation by maintaining a more optimal pH and producing more gas during 24 hours of incubation. Subsequently the reactivity acid titration, sodium bicarbonate maintained greatest (with magnesium oxide/magnesium carbonate supplement) pH of 6.8, similar to optimal rumen. Mean pH of the calcium magnesium carbonate, fines A did not differ from the blank and was less than that of the other mineral buffer incubations (Table 3).

 

The distribution and ranking of TACC and incubation pH values among the supplements were consistent with previous reports of sodium bicarbonate and magnesium oxide (Schaefer et al., 1982). Results were also consistent in that indirect measurements of diet degradation (gas production) increased with increased pH of the incubation.

 

Nutritionist significant role is to aim to maintain a healthy rumen ecosystem while cost effectively sustaining levels of thriving milk production and performance. Nutritional additives for buffering supplements in dairy cow diets are a function of salivary buffer secretion, feedstuff buffering capacity, acid-producing potential of the diet and feed acidity. Saliva in cattle contains 125 milliequivalents (meq)/L bicarbonate and has a pH of 8.4. The production of saliva is much higher when roughage is consumed than when grains are consumed. Important factors for saliva secretion are the dry matter content of the feed and intake, forage intake and particle size. Thus dry matter intake (forage) plays an important role in amount of buffer required by the cow.

 

Buffers help to promote thriving rumen micro flora and fermentation, by resisting changes and maintaining optimal rumen pH. A buffer is a combination of a weak acid and its salt and resists changes in pH or hydrogen ion concentration. A model rumen buffer should react and tie up available hydrogen ions and have an equivalence point of pKa near the desired pH – 6.2-6.8 in rumen.

 

An alkali may also help rumen function from excess acid production; compounds with higher pKa (alkalis) are also beneficial in obtaining optimal rumen pH by increasing overall pH. Sodium sequiscarbonate contains a mixture of sodium bicarbonate and sodium carbonate (alkaline). The pH of a one percent solution of sodium sequiscarbonate is 9.9.   Magnesium oxide (alkaline) and other mineral supplements, such as calcium magnesium carbonate are also considered as possible sources to increase pH. Research studies have indicated combination of both positive as well as no effects from these mineral feed supplements- alkalizing agents to show effect in rumen and milk production/quality.

 

Sodium bicarbonate is an ideal buffer with an equivalence point of 6.2-6.4 near optimal rumen pH and will help resist changes in pH by its own buffering capacity. Feed grade sodium bicarbonate is the overall standard rumen-buffering supplement. It is endogenous to the cow as the greatest component of saliva and effective natural buffer.

 

Sodium bicarbonate is added to the diet to replace endogenous deficiencies in saliva production, which can occur when cows consume a high grain diet. According to Mertz, et. al. (2009) rumen pH also decreases when cows in high producing herds are fed highly fermentable carbohydrates, in transition dairy cows, in cows in peak lactation with high dry matter intake, and in cows at peak milk production.

 

Acid neutralizing capacity can vary significantly with different physical and chemical characteristics of dietary buffers and alkalizing agents. Some buffers/alkalis dissolve within minutes after entering the rumen, others dissolve so slowly that they largely pass from the rumen before dissolving. Ideally, buffers or alkalis should either be released during the interval of most severe acid production in the rumen, or they should provide a continuous release to prevent fermentation-related increases in free proton, H+concentration from becoming detrimental to fiber digestion.

Results of these preliminary incubations indicate gas production was greatest and a more optimal pH maintained by sodium bicarbonate than any other supplement. Rumen pH can affect the relative proportions of rumen microbes (fibrolytic vs. non-fibrolytic, etc.) and the quantity and ratio of end products produced (VFA, etc). By resisting changes in pH and, maximizing fermentation, the cow obtains more VFA for energy and more microbial protein. Ondarza, B (2006) found that sodium bicarbonate supplementation maintained stable rumen pH over longer period of time; as well she found improved milk production and milk fat. However, the benefits from sodium bicarbonate and other buffers/alkalis were most beneficial in high grain diets and early lactating cows.

 

In several animal studies, combinations of buffers have been found more effective than a single buffer/alkaline in ruminants. Commercial mixtures are currently being investigated. Buffers have different sites and modes of action: therefore, using a combination of buffers has been recommended and maybe beneficial dependent on the combination. The optimum buffering conditions for maximum digestion in the gastrointestinal tract includes combinations of buffers and alkalizing agents that can be used to direct acid neutralizing activity to specific digestive sites.

 

Different studies have tested mixing a buffer with an alkalinizer. (Hutjens, M, 1998) suggested mixing three quarter’s buffer to alkalizer. Sodium Sesquicarbonate is already a mixture of half & half - buffer / alkalizer; that is sodium bicarbonate and sodium carbonate, with a pH of 9.9, different studies have shown positive results similar to sodium bicarbonate. However, we must remember the difference between a buffer and an alkaline. A buffer will hold pH stable around its range near pKa, it has a buffering capacity and should maintain a more stable pH overtime as free hydrogen ions are released, i.e. more acid or alkali addition.

 

According to Webster- (a buffering agent adjusts the pH of a solution. The function of a buffering agent is to drive an acidic or basic solution to a certain pH state and prevent a change in this pH). For example, sodium bicarbonate has a pKa 6.2-6.4, with a pH near 8.4. Supplementing with sodium bicarbonate, a pH of 8.4, raises the pH a degree (acidic rumen) and holds a stable pH around pKa of 6.2-6.4- optimal to rumen and to buffer (sodium bicarbonate).

 

Alkalis have a pH above 7, most commonly thought as a substance that can accept hydrogen ions or hydroxides. An alkali- (base) will react immediately with acid to neutralize and produce water and salt. It is unlike a buffer, in that the reaction immediately occurs and it does not drive to a certain pH and prevent changes in pH. It also depends largely on the degree of acid or available hydrogen ions, as well as amount of alkali added and the strength of alkali- level of pH. Magnesium oxide has some similar effects as sodium bicarbonate (increase rumen pH) but it is not a buffer, it is an alkali. As well sodium sesquicarbonate is a mixture of sodium bicarbonate and sodium carbonate, and it too is a neutralizer, wit pH 9.9. There are also multi-element packs, which contain buffers and alkalis, dependent on mixture.

 

Other researchers have tried mixing buffer packs (combination of several minerals), and no consistent data has shown an increase beyond standard recommendations. For example West, J. (1998) reported studies that investigate the effects of sodium bicarbonate and magnesium oxide as beneficial, while other studies indicated no additive effects. The preliminary results indicated that a mixture of 50/50 sodium bicarbonate and magnesium oxide/ magnesium carbonate was not as favorable to rumen fermentation as sodium bicarbonate alone. According to (Hutjens, M, 1998) a sensible combination may have the most favorable effect in rumen He recommends a 75:25 buffer to alkaline as an effective combination.

 

Both sodium bicarbonate and magnesium carbonate had the highest rates of reaction in the acid titration reactivity test and showed the greatest ability to maintain a neutralized pH of 6.8 (optimal pH in rumen) with the continual addition of acid to the material. According to preliminary measurements a greater pH and gas production was maintained by sodium bicarbonate than any other supplement. While the magnesium oxide/ magnesium carbonate treatment maintained an elevated pH over magnesium oxide and calcium magnesium carbonate (comparable to blank). Sodium bicarbonate is an ideal buffer with an equivalence point of 6.2-6.4 near optimal rumen pH and will help resist changes in pH by buffering capacity. The distribution and ranking of TACC and incubation pH values among the supplements were consistent with previous reports of sodium bicarbonate and magnesium oxide (Schaefer et al., 1982). Results were also consistent in that indirect measurements of diet degradation (gas production) increased with increased pH of the incubation.

Given the significant influence of the rumen on the overall nutrition of the cow, the number and variety of attempts to better understand and manipulate this intricate ecosystem are not surprising. According to Rode, L. (2000) nutritionist limitless methods of solving nutritional imbalances or increasing milk production and milk fat may be counteracted towards the modern cow and their genetic potential for milk production. Cows must rely on additional nutritional supplements; higher ration energy density allows cows to obtain necessary energy for greater fermentation and maximized milk production, this in turn will lead to low rumen pH; depressing fiber digestion and to digestive problems and metabolic disorders. A better understanding of the overall nutrition of the cow and whole rumen ecosystem will allow us to sustain a fine balance between the modern cow productivity, proper digestion and acidosis.

 

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