Suckler cows are susceptible to grass staggers for a number of reasons because their main foods consist of rough grazing and coarse fodders (hay and straw), both of which are low in magnesium and even the magnesium in them is not readily available.
The cows are also often kept under exposed conditions in wet, cold areas. In addition, cows become very much more prone to grass staggers with increasing age.
The acute form of grass staggers is the result of a gradual lowering of the magnesium level in the blood due to the deficient diet.
Stresses like a heat period, calving or severe weather often precipitates this condition. Suckler herds can suffer from acute forms of the disease in any month from September to June depending on local conditions and the breeding pattern. Autumn and winter calving herds are particularly susceptible from October to December.
There are other factors affecting the availability to the cow of magnesium in her food or the amounts of magnesium in the feed which are related to fertiliser practices on the grassland.
The incidence of grass staggers has been shown to increase when spring dressing of potassic fertilisers and/or slurry – especially poultry slurry – have been used. The potassium depresses the magnesium content in these grasses and probably also the availability of magnesium to the cow.
Heavy application of nitrogenous fertilisers also appears to lower the availability to animals of the magnesium in the grasses. There is, too, a seasonal variation in the magnesium content of pastures with the lowest occurring in the spring when the cattle are first turned out. Older leys, permanent pasture and clovers tend to have higher magnesium values than short term ryegrass leys.
The prevention of grass staggers is now well understood since the discovery that the feeding of supplementary magnesium as magnesium oxide was fully effective.
Two ounces of magnesium oxide fed daily will prevent nearly all traces of grass staggers and this can be incorporated in the concentrate feed for a nominal charge.