Grass staggers (hypomagnesaemia or grass tetany), caused by low blood magnesium levels, could be more of a risk in cattle this spring where farms have experienced excessive winter rainfall, according to Rumenco’s Technical Services Manager Dr Alison Bond.
Common sub-clinical symptoms, including reductions in milk yield and feed intake, will directly impact performance in dairy and beef suckler herds, she says, whilst a small percentage of cases may result in ‘downer cows’ due to muscle dysfunction, or death.
“Magnesium deficiency is often a risk in the spring, as typical seasonal conditions conspire to impact on its availability,” she explains. “These can include a dilution effect in lush fast-growing grass, for example, or magnesium uptake being inhibited by late frosts or early applications of nitrogen and potassium fertilisers.
“This season, where many farms have endured excessively high rainfall over the winter months, risks of deficiency could be higher than usual, with minerals including magnesium being leached from soils at a greater rate.
“Providing supplementary magnesium as a routine is the best strategy, because once symptoms become evident, even in a small number of cattle, a lot of damage will already have been done.”
Dr Bond points out that the average lactating suckler cow requires 26g/day of magnesium, or around 0.2% of her daily dry matter intake. However, assuming a daily dry matter intake of grazed grass of 13kg/day, the cow will be significantly deficient during the peak grass growing period.
“Spring grass will typically have a magnesium level of just 1g/kg of dry matter, so – on a grazing only diet – the cow is receiving only 13g/day, or about half of her 26g/day requirement. These figures apply to an average spring, so the deficiency is likely to be greater where farms have endured a very wet winter. When a similar calculation is made for dairy heifers, for example, the deficit in an average spring is around 20%, so also significant.
“Supplementation is essential at this time of year to make up the shortfall, thereby avoiding often invisible sub-clinical losses, or the more obvious symptoms like reduced intakes, lower milk production, hyperexcitability, muscle spasms and starey eyes, for example.”
Free access mineral blocks and buckets are, according to Dr Bond, the most reliable and cost-effective way to supplement magnesium, as well as other important vitamins, minerals and trace elements. She recommends Rumenco’s Supalyx Magnesium bucket, which contains 15% of palatable bioavailable magnesium as well as other minerals, vitamins and trace elements. Alternatively, she advises the provision of Maxx Cattle Mag, also formulated with a highly palatable and bioavailable magnesium source.
“Palatability and bioavailability are key points with these formulations,” she adds, “and supplementing with blocks or buckets allows free access for all stock, with minimal labour requirements.
“Magnesium deficiency is in many ways an invisible source of losses in cattle, so making it easily available in this form during the high-risk months will be an effective preventative measure for many.”
