One of the most eﬀective ways to prevent grass tetany in dairy cows is magnesium supplementation during the risk period. Choosing the supplementation source is quite challenging in practice, magnesium oxide is commonly used to prevent Mg deﬁciency, but the solubility and therefore the bioavailability varies greatly in practice (1).
Choosing the right magnesium source
pHix-up is a product with a 48.5% magnesium content, which is also highly soluble, making it a great source of Mg during the grass tetany risk period. The ruminal solubility of pHix-up was evaluated in artificial rumen using rumen juice from Holstein cows, at a pH level of 6.5. The results showed a solubility in the ruminal stage of more than 85%, meaning that pHix-up releases a signiﬁcant amount of soluble magnesium available for ruminal absorption. Other sources of MgO have a large variability of the solubility in rumen juice (40-70%).
Dosage of magnesium supplement
In order to have an eﬀective prevention of grass tetany, magnesium supplementation should be started several weeks before the tetany risk period, in order to get the animals accustomed to it. This supplementation must be maintained throughout the high-risk period (2), (3).
The recommended magnesium supplementation dosage is 28-56 g/cow/day (4). beginning at least two weeks before grazing fresh pastures until these pastures are more mature and the grass tetany risk is reduced.
pHix-up is a product containing 48.5% Mg thus a dosage of 75-115 g/cow/day provides 36-57 g/cow/day of highly soluble magnesium, which brings the additional protection needed during the grass tetany critical period.
(1)Rayburn E., Matlick D., 2012. Reducing the risk of grass tetany, West Virginia University. (2)Elliott M., 2009. Grass tetany in cattle – treatment and prevention, Extensive Industries Development, Primefact 421. (3)Grunes D.L., Mayland H.F., Controlling grass tetany, Agricultural Research Service and Extension, United States Depart-ment of Agriculture, Leaﬂ et nr. 561. (4)NRC 2001; INRA 2018