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With only weeks to go before the main start of calving, dry cows should be on pre-calving minerals and vitamins by now.
Generally, these should be fed for six weeks prior to calving.
Whether they are necessary and what mineral to buy all depends on the mineral analysis of the feed being fed.
Supplement
Remember, there are minerals in all feed stuffs, the minerals that are bought in bags or in licks are used to supplement what is in the diet.
With some farmers supplementing silage with straw and meal this year, the amount of minerals being consumed in the overall diet is different to normal, so getting a mineral analysis of the diet completed is sensible.
This analysis of the dietary mineral composition can then be used to forumate a mineral supplement.
However, most farmers will buy an off-the-shelf mineral. The options are powder, licks or in the water.
Specs
In terms of spec, the dry cow requires between 20g and 25g of magnesium per day before calving.
If the label says there is 20% magnesium in the mineral mix and you are feeding 120g per day, then the cows are getting 24g of magnesium per day.
The next big one is phosphorus. Not all minerals will have phosphorus included, but most cows need around 4g/day before calving.
For selenium, the target is for 5mg or 6mg per day pre-calving.
If it says there is 50mg on the label and if 120g per day is fed, then the cows will be consuming 6mg per day.
Iodine should be fed at not more than 12mg per cow per day.
Forage
When it comes to forage, cows should be on a low potash and high magnesium diet before calving.
Some silages are high in potash and this will prevent the cow from mobilising magnesium after calving.
Magnesium is used in the body to speed up the absorption of calcium from the bone.
So feeding cows extra magnesium pre-calving will help to prevent milk fever, particularly if the silage is high in potash.
Increasing the magnesium level to 40g per day when silage is high in potash or in cows close to calving is a good policy to prevent milk fever and other metabolic problems.
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