ISSUE FOCUS 36 FEED & ADDITIVE MAGAZINE November 2025 materials for which an ABC-4 determination of individual batches/origins is recommended. The same applies to other low soluble oxides and carbonates (e.g., MgO, MnO, CaCO3). Their acid buffering capacity is theoretically very high, but can vary significantly depending on origin, purity and particle size, which justifies individual batch analysis. Calcium and magnesium phosphate salts (0 to 4000 meq/kg), obtained by the treatment of the aforementioned carbonates and oxides with phosphoric acid, have different ABC-4 values as a function of the relative amount of phosphoric acid used for neutralization. Monocalcium phosphate (MCP) and dicalcium phosphate (DCP) are nutritionally similar, but the former has a low pH and negligible or slightly negative ABC-4, whereas the latter buffers acid(ity) and has high positive ABC-4. Analogously, not all magnesium phosphates have the same buffering effect. If available, use phosphate salts with low ABC-4 values, as they also offer the best phosphorus availability. When selecting organic acids during feed formulation, several factors (impact on feed palatability, anti-microbial effect, gut health improvement) must be taken into account. In the context of ABC-4, their acidification power to lower buffering capacity and improve the digestibility of the feed is most relevant and differs greatly (-12000 to -1500 meq/kg) between acids as a function of concentration (e.g., 100% fumaric versus 50% lactic acid), acid strength (pKa value), and molecular weight. In buffered organic acids and salts of organic acids (e.g., calcium propionate), part or all of the acidification power has been removed. These types of raw materials may be equivalent to the organic acids themselves in terms of organic anion sources (e.g., lactic acid and calcium lactate are both sources of lactate) but from an ABC-4 perspective, they are completely opposite. Fully neutralized salts of organic acids do not acidify at all. On the contrary, they actually increase the pH as can be seen from their positive ABC-4 value (4000 to 10000 meq/kg). THE ROLE OF PROCESSING Processing of feed ingredients may alter their ABC-4 value, depending on the type of treatment. In general, enzymatic treatment alone has limited impact, unless it requires significant pH correction to maximize the enzyme’s hydrolytic activity. The impact of fermentation (e.g., of soy protein sources) depends Bicarbonates Organic Acids Organic Acid Salts Starch Sources Fiber Sources Food By-products Milk-Derived Products low high low high Sulfates Sugars Fats Soy Proteins IMPACT VARIABILITY Fish Meal Phosphates Manganese Oxide Magnesium Oxide Zinc Oxide Calcium (Magnesium Carbonate) Figure 3. Qualitative evaluation of the variability of ABC-4 values of classes of feed ingredients and their impact on the ABC-4 value of complete feed
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