A good part of calcium in most feeds remains unaccounted for as it is hard to control the inputs of this cheap mineral.
There is much talk going on about calcium in diets for monogastric animals. Too much, and it interferes with other mineral nutrition; not enough, and it will harm productivity. But there is hardly a case where calcium will be found deficient in well-manufactured commercial diets. In fact, every lab analysis comes back almost invariably high in calcium. Have you ever wondered why? Here are the primary reasons:
Natural ingredients contain more calcium than accounted for; the reason is explained by the following bullet points.
Chemical laboratory analyses have a margin of error 20 percent, plus or minus. This is the accepted norm by most official organizations. So, if your sample is supposed to contain 1 percent calcium, lab results ranging from 0.80 to 1.20 percent calcium are absolutely normal.
Limestone, the most common source of calcium in all animal diets, is a highly variable ingredient containing an unknown amount (unless analyzed) of calcium ranging from 22 to 38 percent (in theory). The latter is impossible as it refers to pure calcium carbonate.
To make matters worse, limestone is used as a cheap universal carrier for all premixes, as a filler for concentrates and so on. In essence, it is everywhere. Of course, high quality products contain pure calcium carbonate, but this does not negate the fact that they contain calcium, often unaccounted for on the label.
Calcium requirements for most animal species have been determined a century ago (OK, at least in the previous century). So, we tend to be overgenerous with safety margins as calcium sources are cheap.
Phytase, a common enzyme, releases calcium, which is often unaccounted for in feed formulation.
Soybean meal, a universal ingredient, is often supplemented with 0.5 to 1.0 percent limestone to increase its flowability.
The above help illustrate the fact that monogastric animals receive a surplus of calcium, a good part of which is often hard to control and remains unaccounted. The only remedy is to test complete diets for calcium and make necessary adjustments. Lamentably, this needs to be done frequently enough, especially when formulas change on a routine basis.