Hypocalcaemia or milk fever and hypomagnesaemia or grass tetany (GT) are two metabolic disorders of concern to dairy industry. These disorders usually occur in early lactating cows that have not received adequate supply of calcium and magnesium from rations or through reserve mobilization during lactation. The risk of cow developing milk fever or grass tetany can be related to the mineral composition of their rations. The dietary cation-anion difference (DCAD) of a ration, with is a parameter related to milk fever incidence, can be calculated as follows: 

DCAD = [(K⁺ + Na⁺) – (Cl^- + S^2-)]

Where DCAD is express in mmol/kg dry forage matter

Ration too rich in K⁺ and Na⁺ slightly increases the blood pH. This decreases the efficiency of calcium mobilization from bones, making cow more prone to milk fever. A ration rich in anions, such as chloride and sulfur causes blood to become slightly acidic. This favors more efficient calcium mobilization from the bones, reducing the risk of milk fever. The risk of grass tetany occurring in the animal can be determined by the GT index:

  GT Index = K⁺ / (Ca²⁺ + Mg²⁺)

The occurrence of grass tetany is greatly increased in cattle grazing forage with GT index higher than 2.2.

The management of K in the forage can be critical, as there is a tradeoff between meeting the metabolic requirements of the forage crops and those of animal. For dairy cows, excessive K in forages not only causes metabolic disorders like milk fever and grass tetany, but it is also associated with immune suppression  followed by many opportunistic and infectious diseases. One solution to high K forage is to apply controlled amount of K fertilization for desired forage growth. Fertilization with calcium source is recommended for decreasing K to Ca ratio, and likely to discourage the growth of endophytic and other pathogenic fungi in pasture forage. – Excessive K in forages is known to be the cause of the fungal growth.

To improve the quality of forage for animal consumption, it is important that while protein level is maintained attention should be paid to control the DCAD and GT index. The DCAD value of the forage can be reduced by increasing the anionic content. Both chloride and sulfate are effective. But, chloride is more efficient in acidifying the blood than sulfate. Being highly soluble, it is weakly retained in the soil and is readily available to the plant roots, which then transferred to forage crop. Studies at the Miner Agriculture Institute at Chazy, NY, have shown very high percentage, almost all, of chloride applied to the soil being transferred to the crop.

Hi-Cal liquid calcium is an excellent source of both chloride and calcium.