Milk fever is a multifactorial disorder that often results in a range of related disorders, which, in the final analysis, can lead to loss of longevity in cows, listlessness and have financial ramifications.
Should we make our dry cows acidic?
How can we solve the problem of milk fever? There are also many answers to this problem, and what works for one farmer, will not necessarily work for the next.
Dry cows in most herds used to be given a ration consisting of the cows’ TMR supplemented by extra straw. This is a practice still in use in a lot of places, and successfully in some herds, but most highly productive cows need their own ration, which takes into account the needs of a dry cow with regard to energy concentration, protein, DCAD (dietary cation-anion difference), vitamin and mineral levels (including extra focus on calcium etc.).
In those herds where it is practically possible, it is very often an advantage to divide the dry cows into a far-off group and a close-up group, as those farthest from calving have a lower energy requirement than those close to calving.
In the battle against milk fever, keeping the DCAD value low is important, especially in the last three weeks up to calving. This can be achieved by focusing on the ingredient composition of the ration, where there can be considerable variation in the DCAD value of different ingredients, or acidogenic (or anionic) salt can be added. And which acidogenic salts should be used is another topic on which there are many opinions.
Magnesium sulphate has a low DCAD value of -16.625 meq per kg dry matter. This is currently one of the most frequently used acidogenic salts, due to the low DCAD value and low price. Magnesium sulphate works best in dry cow rations when only moderate addition of acidogenic salts is needed, as a high level of addition can mean an unsuitably high level of sulphur, which can be harmful to the cow’s rumen environment. But we rarely encounter negative reports on the use of magnesium sulphate in practice.
Another frequently used acidic salt is magnesium chloride, which contributes a less negative DCAD value than the sulphate, of around -9.831 meq per kg dry matter, and is more expensive than the sulphate. Magnesium chloride has the advantage of not contributing sulphate to the dry cow ration, and is water-soluble, in common with the sulphate. When a high level of acidogenic salts is needed to reduce the DCAD value to a low level, combining the addition of magnesium sulphate and magnesium chloride can be beneficial.