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Magnesium boost could reduce slow calving risk

14 February 2020

Farmers are being advised to increase the level of magnesium in minerals given to suckler cows before calving after new research found they absorb less than previously thought.

SAC Consulting, part of Scotland’s Rural College (SRUC), has issued the advice after new information from the USA found magnesium from rock sources has around half the absorption levels of past estimates.

Magnesium is critical for both the prevention of staggers and to help cows mobilise calcium reserves and minimise the risk of slow calvings.

The National Research Council (NRC) in the United States brought out the 8th edition of Nutrient Requirements of Beef Cattle in 2017 and Professor Bill Weiss, who is now working on new dairy cow recommendations, has given some indications of changes they are making to availability for magnesium.

They suggest that magnesium from rock sources has around half the absorption levels than was previously thought.

Magnesium oxide is the most common form used in mineral supplements in the UK and Karen Stewart, a livestock nutritionist at SAC Consulting, said given the recent information, depending on the diet, it would be advisable to increase magnesium in suckler cow pre-calving minerals.

“The current guidelines is 10 per cent magnesium in a pre-calving mineral for normal silage rations and I think the revised absorption coefficients would justify an increase to 15 per cent magnesium to take account of the reduced absorption,” she said.

“Magnesium plays a vital role in helping cows mobilise their own reserves of calcium to help with muscle contractions. Low magnesium is associated with slow calvings.”

She added: “If staggers is considered a particular risk or the silage has particularly high potassium levels as a result of slurry applications, further supplementation may be considered.

“This spring the risk of slow calvings will be higher as a result of cows being high body condition score.

“Getting a full silage analysis including minerals, and planning pre-calving rations with nutritional advice, will be particularly important ahead of spring calving 2020.”



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