Magnesium supplementation is an essential part of transition management on dairy farms.
Severe magnesium deficiency will cause nervous signs and often death around the time of calving. Mild deficiency will suppress appetite and milk production. Magnesium is also linked to hormones that help maintain blood calcium levels and hence plays a very important role in milk fever prevention.
Dairy cattle require between 12 and 20g of elemental (pure) magnesium per day over the transition and early lactation periods, depending on their bodyweight. The table shows the number of grams of each product the cow must be given to achieve the required dose of pure magnesium.
|
Magnesium source |
Pure magnesium content |
Dose of product needed to receive required dose of magnesium (g/cow/day) |
|
|
16g 20g |
|||
|
Magnesium oxide (MgO) |
55% |
29 36 | |
|
Magnesium sulphate (MgS) |
10% |
162 202 | |
|
Magnesium chloride (MgCl) |
12% |
134 167 |
If the magnesium salts, MgS and MgCl, are fed pre-calving, they are likely to be better at preventing milk fever than MgO due to the Dietary Cation Anion Difference (DCAD) effect. MgS and MgCl have a low pure magnesium concentration and the dose required to achieve adequate levels of magnesium makes the water taste bitter. Doses above 60g/cow/day of MgS or MgC increases the risk of reduced water intake and in the case of MgS may cause diarrhoea. One way to get around this is to supply the cows with 60g/cow/day of MgS or MgC through the water and also dust the pasture/silage with
50-70g of MgO.
Magnesium supplementation should begin 3 weeks prior to calving. When to stop will depend on the property. Most should continue through the mating period.
Cows can be blood tested to check if they are receiving enough magnesium. Contact Totally Vets for advice on supplementing with magnesium.
