Calcium (Ca)

What it changes in the tools

Calcium : phosphorus

Below 1.0 the ratio is inverted — poor bone mineralisation, and on grain-heavy diets urinary calculi in male stock. Ruminants tolerate roughly 1:1 to 7:1 once absolute calcium and phosphorus are met.

Source: NASEM (not critical unless above 7:1 or below 1:1); Merck/MSD (at least 2:1 for calculi).

DCAD, for a springing cow

Calcium is not in the DCAD equation itself, but DCAD governs whether she can mobilise her own at calving, and on a transition diet the aim is to pull it DOWN. The published prepartum goal is below +50 meq/kg DM or negative, with the stronger target −50 to −100 where anionic salts are used. New Zealand pasture is strongly cationic — measurements run about +200 to +900 meq/kg — so a springer grazing grass is nowhere near that, and the standard answer here is magnesium for the last three to four weeks rather than full anionic salts. Worth knowing: DairyNZ report that ordinary pasture potassium (1.0–4.5% of DM) does not by itself raise milk-fever risk, so chasing low-potassium feeds pays mainly on effluent or heavily fertilised paddocks. We raise this as a watch for a cow within 28 days of calving — including a rising-2 heifer still growing — and leave it as a plain reading for every other class, because the target applies to nobody else. Milk-fever prevention is a conversation with your vet. (A cow you are still milking reads on the lactating scale instead, where the fitted optima are about +340 meq/kg DM for milk yield and +400 for intake.)

Source: Prepartum goal and target: Beede 2007 (Michigan State / DAIReXNET), “less than +5 meq/100 g DM” or −5 to −10. Pasture potassium: DairyNZ. Lactating optima: Hu & Murphy (2004), J. Dairy Sci. 87:2222–2229.

Which feeds carry the most calcium

From the cited composition of every feed in our library, as a percentage of dry matter. Useful when the answer is a feed change rather than a mineral product.

Mineral products, if you're dosing

Dosed in grams per head per day rather than fed by the kilogram — a different decision from changing the diet, so they are listed apart from the feeds.