Grass tetany (hypomagnesaemia), caused by low blood magnesium levels, could be more of a risk in lactating ewes this spring where farms have experienced excessive winter rainfall, according to Rumenco’s Technical Services Manager Dr Alison Bond.
Common symptoms, which include reduced milk production in ewes, will directly impact lamb performance, so sheep farmers should be extra-vigilant and take preventative action to avoid unnecessary losses, she advises.
“Magnesium deficiency is often a risk in lactating ewes, as typical spring conditions conspire to impact on availability,” she explains. “This 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 sheep, a lot of damage will already have been done.”
Dr Bond points out that the average lactating ewe requires 4g/day of magnesium, or around 0.2% of her daily dry matter intake. However, assuming a daily dry matter intake of grazed grass of 2kg/day, the ewe 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 ewe is receiving only 2g/day, or about half of her 4g/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.
“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, loss of body condition and greater susceptibility to disease.”
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, Rumevite Magnesium, also formulated with a highly palatable and bioavailable magnesium source, is available as a fourteen inch block.
“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 sheep flocks, so making it easily available in this form during the high risk months will be an effective preventative measure for many.”
