Multi-purpose tools have great on-farm value because they serve a variety of functions and save time, energy, and money. Nutritionists and producers should assess feed ingredients through the same lens, particularly those included in their buffer packs. Calcium magnesium carbonates, commonly known as dolomites, can fill a variety of roles in the diet, impart a variety of health benefits to the cow, and reduce overall ration cost. Let’s take a closer look.

What’s in a dolomite?

Dolomites have been used in animal agriculture for decades, initially as buffer sources in feedlot cattle and more recently in dairy cattle diets. They are naturally occurring minerals that contain an equal proportion of magnesium carbonate (MgCO₃) and calcium carbonate (CaCO₃). Thus, they are also called calcium magnesium carbonates.

The value of multi-purpose feed ingredients.

Pure calcium magnesium carbonates have a relatively high magnesium concentration of around 12% and a calcium concentration of 22%. Their carbonate form also allows them to act as alkalizers. Though these products have a slightly different mode of action than buffers like sodium bicarbonate, they do act similarly in the rumen of cattle by helping to raise pH.

The unique composition of dolomites allows them to fulfill multiple roles in the ration of a dairy cow— calcium source, magnesium source, and dietary buffer. This gives nutritionists the ability to replace calcium and magnesium sources, such as limestone and MgO, as well as more traditional buffers, such as sodium bicarbonate, with a single ingredient. It also results in significant economic and ration space savings to the dairy.

Careful selection is key.

Like many other feed ingredients, not all dolomites are created equal. Most dolomites marketed in the dairy cattle feed industry are by-products of other industries such as soil pH amendment and glass production. These dolomites often come with little quality assurance and no product-specific research. In one comparison, a dolomite of mixed origin saw a 35% reduction in solubility over a 3-year timespan.  During this same time period the solubility of MIN-AD®, a high-quality calcium magnesium carbonate mined exclusively for animal feed, maintained a consistent acid solubility. While solubility is not directly indicative of mineral bioavailability in the cow, this comparison does show the inconsistency typical of dolomite byproducts.

One of the challenges when evaluating dolomite sources is determining bioavailability. Because it is difficult and cost prohibitive to measure actual bioavailability of dolomites, most companies resort to using in vitro solubility tests to predict bioavailability. This approach can be risky. Solubility is a thermodynamic property that depends, sometimes very strongly, on factors such as temperature, pressure, partial pressure of gasses like CO₂, and acidity. Considering this wide range of variables, solubility in an in vitro system does not equate directly to bioavailability.

In support of this idea, a 2017 survey conducted by Dr. Dave Beede cites a study in which an MgO source with the lowest in vitro solubility had the greatest numerical effect on dry matter intake, milk yield, fat corrected milk yield, and milk fat. He concluded: "Overall, it does not appear that the in vitro solubility test in a buffered system suggests anything about lactational responses." Because of these key difficulties, the best way to evaluate the effect and value of dolomites is through controlled research trials.

One such in vitro trial compared MgO, MIN-AD, and a dolomite by-product with a particle size distribution and chemical assay similar to MIN-AD. There was an increase in propionate and total volatile fatty acid (VFA) production in the MIN-AD treatment that was not observed in the chemically similar by-product dolomite. This again highlights that source matters when it comes to dolomites. Additionally, numerous in vivo trials conducted at universities and commercial dairies have supported the effectiveness of MIN-AD in rations. Most recently, work out of the University of Saskatchewan demonstrates MIN-AD’s ability to buffer the hindgut and reduce leaky gut.

When evaluating calcium magnesium carbonates, caution should be taken if basic solubility data alone is presented as proof of bioavailability. Look for products that have been tested and proven to support dairy cattle in a variety of ways. This is where the difference really matters and what makes calcium magnesium carbonates valuable feed ingredients.

Article by Clayton Stoffel, Papillon Technical Service Manager.