Where do they come from and how they are used?


Take-home messages:

There are both sodium (Na)-based and potassium (K)-based feed additive compounds available for buffering and alkalizing the rumen.
Sodium buffers will always be the lowest cost DCAD source.  Potassium carbonate is a strong alkalizer (almost 2X Na buffers) and K has health benefits beyond just DCAD.
Sodium bicarb and Na sesquicarbonate are functionally equivalent but Na bicarb may have more versatile application.
Specialty (low-reactive) K carbonates are invaluable in climates where humidity increases the risk of storage issues or ingredient cross-reactions in dairy blends.
Branded specialty K carbonates vary significantly in their K content.  Failure to account for this in formulation leaves hundreds of dollars per ton on the table. 

Background:  

The structure of the dairy feed production chain lends itself to potential confusion relative to the usage of feed ingredients.  There are many macro ingredients used and a dazzling array of micronutrients and additives to keep straight.  This confusion can be made worse by product branding and unique positioning of seemingly identical materials.   It can also be problematic that decision-making relative to ingredient purchasing and usage is somewhat decentralized.  Most manufactured dairy blends (to be added to a TMR) are based on custom formulas.  In the common case, a field nutrition consultant creates a proposed base mineral/protein formula that is then bid out to regional blenders.  The blenders then attempt to produce a cost-competitive rendition of that formula, within the confines of their business model.  The problem with this arrangement is that success often depends on both parties having a good understanding of the availability and the chemical/physical characteristics of key ingredients.  Only good ingredient training, mutual transparency, and good communication on formula constraints assures that this process works seamlessly. 

In the Midwest and Canada, Barentz North America distributes the mineral buffers, sodium bicarbonate and common Potcarb (anhydrous potassium carbonate).  We also manufacture and nationally distribute a specialty stabilized potassium carbonate (K-Carb Plus™).  On the surface, the trade and application of the major buffer products seems very straightforward.  Unfortunately, mineral buffers and  positive DCAD for dairy cows have not been a hot nutrition topic for the past 20 or 30 years.   However, we hear odd anecdotes and get increasing reports from the field suggesting that a quick review of the sourcing and use of these buffers might be helpful to both our customers and to their clients.  

Nutrition 101: What are rumen buffers? What is positive DCAD?

Buffers have long been routinely included in manufactured dairy blends or at the farm. The lactating dairy ration is starch dense (corn or silage) and the resulting rumen fermentation challenges the cow’s ability to neutralize and clear the volume of rumen acids produced. Excess rumen acid (low rumen pH) can lead to poor forage digestion, low feed intake, and many other health problems for the cow. The main goal of mineral buffers is to supplement the cow’s natural buffer system to essentially risk-manage against possible excess rumen acid. Buffer ingredients act by either classic buffering which “resists” pH change (bicarb’s main effect) or by blunt force alkali neutralization of the acid (a carbonate’s main effect). At the low levels of buffers we add to the ration (< 1%), the cow is happy in any case, but alkali carbonates carry the caveat of being a bit more chemically corrosive.

In the 80s and 90s, research began to show the additional value of the electrolyte function of sodium (Na) and potassium (K) buffers to cow health, especially during warm weather. Generally, only Naand K buffers provide electrolyte value. This contribution shows up in formulation software under a calculated number called positive DCAD (see internet for “dietary cation-anion difference”). For clarity, chloride salts, such as plain salt or potassium chloride make no net contribution to +DCAD, because the Cl- ion in salt offsets the +DCAD value of the Na and K on a one-for-one molecular basis. While just about every nutritionist will have defined strategies for using buffers for rumen health, many only passively monitor the calculated +DCAD value, at least until heat stress becomes a more serious threat. 

Other niche and buffer-like products

For the sake of brevity, in this paper we are going to focus only on the major Na and K buffers used by the industry (Table 1). Although there are many other mineral products that can contribute to rumen buffering, including magnesium sources, clays, and marine algal products, these materials are sometimes a thicket of special market positioning. They also represent a relatively small volume of the total buffer products used by the industry. 

Trona-derived sodium buffers (bicarb and sesquicarbonate)

Trona is a mined material that comes from giant subsurface deposits of evaporated mineral from prehistoric lakes. In North America, we are blessed to have the largest such deposit in the world, located in the broad Green River area of Wyoming. Trona ore is unrefined (~90% pure) sodium sesquicarbonate which is a double salt of roughly 46% Na carbonate (soda ash) and 36% of actual Na bicarbonate. The main business activity of the mines is converting trona ore to 100% soda ash (Na carbonate). Commercial Na bicarbonate (all grades) is then produced by converting refined soda ash back to 100% Na bicarbonate using a carbonation step. There are several major companies operating near Green River and together they produce more than 90% of all the trona-derived sodium products used in the U.S. 

Trona vs Na sesquicarbonates (s-carbs)

 Table 1 shows the three trona-derived buffer products: Trona, Na sesquicarbonate, and Na bicarbonate. Confusingly, on tech or specification sheets, trona and s-carb are sometimes used interchangeably; trona being an ore category and s-carb a chemical term. To make a commercial s-carb, 5 to 10% inert “gangue” materials (shale, mudstone, etc) are physically sorted out to arrive at a 95-98% pure s-carb. When purchasing a product branded as a trona, you should probably assume the inert materials are there and pay closer attention to quality indications. 

While domestic trona materials are quite safe, in other world regions, trona is sometimes known to have a latent contamination risk of fluoride or other elements. The chemistry of fluoride minerals is complex and fluorine toxicity can be unpredictable relative to analyzed levels of fluorine. Products with a max fluoride specification should simply be avoided.

Sodium bicarb vs Na sesquicarbonates (s-carbs)

Depending on market conditions, s-carb buffers typically sell at a slight discount to Na bicarb. Compared with Na bicarb, s-carbs have a bit more Na (thus more +DCAD) and slightly more relative alkalizing power (acid neutralizing) than Na bicarb (Table 1). On the other hand, by some measures, the carbonate-containing s-carbs are more likely to be chemical irritants. Older research literature implies that cows may have detected the alkalinity of s-carb and briefly backed off feed in some trials. In addition, s-carbs are contraindicated for free-choice buffer applications. Aside from possible preferences for handling characteristics, etc., these two buffer materials should be considered equivalent for usage in dairy mineral/protein blends.

Potassium carbonate buffers

Potassium buffers have strong cow benefits but a tighter ROI. Dairy cows require little sodium (~0.2% of ration DM) and must have some plain salt, so Na buffers contribute literally nothing to her basic Na requirement. In contrast, K buffers (K carbonate) are fed primarily to meet the cow’s physiological need for K. Forages typically supply most of the cow’s basic requirement for K (~1% of DM). Unlike Na, K is a high turnover electrolyte and its usage seems to increase in proportion to the stress on the cow. Challenges such as early lactation or heat stress can increase the cow’s K needs by more than 50%. There are also side benefits to increased supplemental K, including altered rumen fatty acids with a likely bump in butterfat. Research shows that increasing either K or +DCAD benefits cow health and milk production, especially during heat stress. It seems logical that maintaining a higher ration K will increase the physiological impact of a higher total +DCAD but published research does not make that clear. In a perfect world, most nutritionists would probably prefer to see most of the ration +DCAD coming from K to get the added K benefits. However, K buffers are three to four times more costly than Na buffers. In most milk markets, the ROI on increased +DCAD is probably always acceptable. However, the ROI on boosting K will be highly dependent on the price of milk and its components. A practical consideration relative to using K carbonate buffers is staying abreast of which K carbonate product is actually being used at the mill, as these products vary significantly in their levels of K (see Table 1). 

Potassium carbonate manufacturing and usage

The majority of potassium (potash mineral) is solution-mined from ancient subsurface ocean evaporite deposits as KCl (sea salt). Saskatchewan holds the largest of the world’s such deposits but there are also large deposits and potash suppliers in Eastern Europe and China. Generally, the production process involves electrolytic conversion of liquid KCl to caustic potash (KOH), followed by reaction with carbon dioxide to form liquid 47% K carbonate (K2CO3). Liquid K carbonate is heated to form the dry anhydrous K carbonate (56% K PotCarb) that is used in commercial feed. There is also a large industrial market for dry hydrated K carbonate (K2CO3 . 1.5 H2O) also known as K sesquihydrate. This specialized “rehydrated” form is slightly lower in K (46%) and is used almost exclusively by the dairy feed industry for its greater handling stability 
(see below).

The role of specialty (stabilized) potassium carbonates

Feed-grade PotCarb is one of the touchier feed ingredients, as it is hygroscopic, chemically reactive, and corrosive to metal. Potcarb may chemically react with many dairy ingredients, including acidic or basic minerals, amino acids, bypass fats, urea, etc., with all these reaction risks greatly heightened by high humidity. Manufacturing SOPs for mineral/protein blends are often geared to address Potcarb’s risks through dilution and mixer addition protocols. In lower humidity regions, some manufacturers opt for more granular Potcarbs to help limit blending reactions. In higher humidity regions (or seasons), however, most blenders simply purchase specialty potassium carbonates of known lower chemical reactivity and stability in storage.


Classes of specialty potassium carbonates

Currently, there are two types of stabilized potassium carbonate products, potassium carbonate sesquihydrates and fat-coated Potcarb (Table 1). Potassium carbonate sesquihydrates are produced by carefully titrating Potcarb back to a state of stable hydration. Because the material is now hydrated, it somewhat less hygroscopic and reactive than straight Potcarb. The disadvantage of this approach is a substantial drop off in K content (56% reduced to 48.5% K), essentially due to dilution with water molecules. There are two sesquihydrate products on the market, DCAD PlusTM and K-Pron®. Because of its longtime market presence, DCAD Plus is called for as an almost generic representation of “stabilized” K carbonate. An alternative strategy to altering the reactive chemistry of K carbonate is to reduce Potcarb’s accessibility to moisture and other chemical reactants via physical coating. K-Carb Plus® is produced by coating granular 56% Potcarb with 5% hydrogenated vegetable oil. This greatly reduces Potcarb’s reactivity with the advantage of retaining a K content that is much closer to that of the original material (56% vs 53%K). 

Zeroing in on what really matters for purchasing and using Na and K buffer brands 

Relative to their uses as buffers, there is little difference in the basic quality attributes among domestically produced Na bicarb or s-carb brands. The materials largely come from the same mining region using similar processes. Therefore, we can focus mainly on the service of our suppliers and our requirements and perceptions of physical attributes such as dust or granularity. As discussed above, imported Na buffers are very unlikely to be cheap enough to warrant an implied risk of unacceptable contaminants. 

The situation is much different with K carbonate buffers. They are purchased primarily for the nutritional value of their K with rumen buffering and +DCAD as secondary benefits. More importantly, K carbonate buffers and, in particular the specialty K carbonates, are more costly than Na buffers. In practical terms, this means that seemingly small differences in the K content among products can have large impacts on actual value of the products. In general, specialty K carbonates tend to price somewhat similarly, in round figures about $2,000 per ton wholesale. 

However, K sesquihydrates have only 48.5% K compared with 53% K in coated Potcarb (K-Carb Plus®). This means that K sesquihydrates sell for $4123 per ton of K vs $3774 per ton of K for coated Potcarb. In this case, a net difference of $350 per ton of K means that it is absolutely essential for plant purchasing/formulation personnel to be on the same page as field nutritionists when making requests or changes relative to K sources to be used in a blend. 

 

Table 1.Feed-grade minerals purchased for use as rumen buffers and DCADsources
	Best known brand or nickname	Main nutritional purpose1	Primary nutrient	Inert material	Relative alkalizing capacity	Purchasing or use considerations
Trona-derived sodium buffers
Ground Trona ore (unrefined sesquicarbonate)	Trona	Alkalizer, Buffer	30% Na	< 10%	10	Monitor specs closely, avoid imports
Sodium sesquicarbonate (refined)	s-carb	Alkalizer, Buffer	30.5% Na	< 2%	13	Equal to bicarb in blends or TMR
Sodium bicarbonate (carbonated soda ash)	Bicarb	Buffer	27% Na	< 1%	12	Suitable for top-dress & free-choice
Potassium carbonate buffers
Potassium carbonate (common)	Potcarb	K source, Alkalizer	56% K	< 1%	20	Hygroscopic, reacts* with other ingredients
Specialty potassium carbonates (stabilized)						Less reactive with other ingredients
Potassium carbonate sesquihydrate	DCAD Plus™, K-pron®	K source, Alkalizer, Stabilized	48.5% K	< 1%	17	Lower K% in hydrate form
Potassium carbonate (fat stabilized)	K-Carb Plus™	K source, Alkalizer, Stabilized	53% K	< 1%	19	Higher K than sesquihydrate
1All provide +DCAD in proportion to mineral levels. Stabilized = lower chemical reactivity