Farmers are being advised to increase the level of magnesium in minerals given to suckler cows before calving occurs, after new research indicates that they absorb less than what was previously thought.

SAC Consulting – part of Scotland’s Rural College (SRUC) – has issued the advice after new information from the United States of America 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 eighth 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 improve availability for magnesium.

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 guideline recommendation is 10% magnesium in a pre-calving mineral for normal silage rations and I think the revised absorption coefficients would justify an increase to 15% magnesium, to take account of the reduced absorption,” she commented.

“Magnesium plays a vital role in helping cows mobilise their own reserves of calcium in order to help with muscle contractions. Low magnesium is associated with slower calvings, which can be detrimental to both the cow and the calf.”

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

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

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