Beef cows can experience metabolic disorders such as grass staggers resulting from magnesium deficiency (hypomagnesaemia) or milk fever due to calcium deficiency (hypocalcaemia) around calving time. These conditions can arise from dietary changes, underfeeding, or environmental factors like high soil potassium (K) or low magnesium (Mg) levels.
Milk fever symptoms include lethargy, with cows often lying down and unable to rise. On the other hand, grass staggers can cause cows to tremble, display abnormal skin twitches, or even exhibit aggressive behaviour. If not addressed, both diseases can escalate to coma and eventually death. Effective treatments involve administering calcium borogluconate for milk fever and magnesium sulphate for grass staggers.
Most soils in New Zealand contain sufficient magnesium, with up to 10kg per hectare annually deposited through rain and coastal sea spray. However, areas with pumice soils, like the volcanic plateau, may lack magnesium and require Mg fertilisers.
To counteract grass staggers, soil Mg levels should be maintained between 20-30, with periodic dressings of 5-10kg Mg per hectare. Dolomite and serpentine super are potential fertilisers to boost Mg levels.
High soil potassium can lead to both grass staggers and milk fever. This is because potassium reduces magnesium and calcium levels in plants, affecting the animals consuming them.
To mitigate this, farmers should avoid grazing in high potassium areas, especially those recently fertilised with potassic compounds, until after calving.
Additionally, it’s advised not to give beef cows calcium supplements before calving, as excessive dietary calcium can hinder the cow’s natural calcium mobilisation. In New Zealand, calcium deficiencies are uncommon due to the nation’s young soils and the prevalent use of super-phosphate and lime fertilisers.
For areas with severe magnesium deficiency, magnesium can be supplemented using magnesium oxide powder on feed or a magnesium bolus.
