There are some very high grass covers on most farms. Growth rates have been excellent and some farms have grown over 1t of grass per hectare more than this time last year. In most cases, it is not possible for the milking cows to graze all of this grass, so skipping paddocks for silage will be inevitable on a lot of farms.

However, some farms have up to 20% of the herd left to calve. It doesn’t make sense to be skipping over paddocks for silage, while still feeding silage to dry cows.

Letting spring-calving dry cows out to grass isn’t something we’re used to in Ireland

Letting out dry cows to graze the highest covers makes sense if ground conditions are good and the risk of damage is small and if there is more grass on the farm than milking cows can graze.

Letting spring-calving dry cows out to grass isn’t something we’re used to in Ireland, but it is normal practice in countries such as New Zealand and Australia.

Whether the cows actually calve outside is a decision for the individual farmer, but there is no reason why they can’t if they are in-calf to easy-calving sires and they can be checked easily. In good conditions like we are experiencing now, outdoor calving is more hygienic and there will be a saving in straw as well as silage.

Mineral status

However, the mineral status of grass is not ideal for calving cows and supplementing with minerals while at grass can be tricky. Relative to what cows require, typical grass values are low in magnesium, high in calcium, OK for phosphorus but high in potash.

Feeding more magnesium pre-calving should help to overcome the issues of high potash levels in grass

Being high in calcium, low in magnesium and high in potash is a red flag for milk fever. High-calcium diets pre-calving are not good as they reduce the cows’ ability to mobilise calcium after calving.

Magnesium and potash are all tied up in this calcium mobilisation process too. Ideally, cows should be fed high magnesium and low potash. Feeding more magnesium pre-calving should help to overcome the issues of high potash levels in grass.

That said, grazing high covers on fields that are low in potash or that haven’t received slurry or chemical potash in the last six months should be safe enough.

The other control method is to continue to feed pre-calving minerals with a high magnesium content. Some farmers feed additional magnesium in the form of dusting cal mag or magnesium flakes in water.

In New Zealand, dry cow minerals are sprinkled over a relatively small section of grass and this section is grazed first, before cows are given their full grass allocation for the day. This ensures that all cows get their mineral intakes.