Cooler and more variable weather will increase the risk of grass tetany in lactating cows turned out to graze with a calf at foot.

Cows at most risk are first calved heifers, thin and older cows, animals with a strong dairy influence and those suckling twins.

Make sure herding of cows is frequent and take steps to increase mineral supplementation, thereby lowering the risk of tetany. Outlined are five tips to preventing grass tetany.

1. Magnesium supplementation

Tetany is caused by a lack of magnesium in the diet. Cows cannot store magnesium, so regular supplementation is essential. Therefore, make sure cows are properly supplemented with magnesium.

This can be in various forms, with the most common being lick buckets, a mineral bolus, added to drinking water or powdered minerals.

When it comes to lick buckets, offer one bucket per 10 cows and place in various locations across paddocks. Not all cows will use the bucket, so a secondary magnesium source may be beneficial.

2. Offer high-mag meal to most at-risk animals

Offering 1kg to 2kg/day of a high-magnesium ration to the animals most at risk will lower tetany risk. Meals can be offered in a trough or under a single strand of electric wire.

3. Avoid overgrazing in paddocks

Do not force cows to clean out paddocks tight to the ground in the current rotation. Move cows once covers get low and animals start getting unsettled.

Leaving a slightly higher residual in early April will not lower grass quality in the next rotation. But forcing cows to fully clean out a paddock will put animals under nutritional stress, triggering tetany.

4. Avoid using high-potash fertiliser on grazing swards

If cows are already filtering out to grass, opt for straight nitrogen or low-potash (K) fertilisers to dress grazing paddocks.

Avoid grazing cows on paddocks that got slurry in the past fortnight. Slurry is high in potash.

High potash levels inhibit magnesium uptake in grass, thereby increasing the tetany risk in lactating cows.

5. Offer a temporary fibre source

Offering cows on lush grass some form of long fibre will lower the risk of tetany.

Placing a few flaps of straw or hay in paddocks will increase fibre intake. Powdered minerals can be dusted on the fibre source, again lowering tetany risk.

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