As we have enjoyed a strong autumn and now come into some cooler weather towards the end of the season and the start of winter we must be conscious of the metabolic disorder known as Grass Tetany. Grass tetany (hypomagnesaemia) is a disorder caused by low levels of magnesium in the blood and fluid that surrounds the brain (cerebrospinal fluid). Low magnesium levels can be primary, due to inadequate intake commonly a disease of the late pregnant or lactating cow (magnesium required for milk production is greater than intake and the body cannot store magnesium), or secondary due to reduced absorption in the rumen.
Typically grass tetany will first be noticed due to the presence of animals found dead in lateral recumbency with evidence of struggling. If animals are identified early there will be a typical excitement phase consisting of excited behaviour, galloping, bellowing and staggering. There is then a depression phase involving the recumbent down cow that will eventually die. The development of grass tetany is complex and multi-factorial, however risk factors include the cooler weather associated with late autumn/ early winter, heavily conditioned cows, older cows, high milking cows, mustering and holding cows off feed for a period of time, pastures with short green grass and low legume contents, heavy potassium/ nitrogen fertiliser applications and stress factors (late pregnancy, lactation, age, transport, etc). Outbreaks occur during periods of cold wet weather due to the additional stress load and the reduced grazing during these periods (cows will use their body tissue, particularly fat for milk production).
Grass tetany can be treated by supplementing magnesium levels and supportive care, however due to the timing of disease development, once a cow is down the prognosis quickly worsens. Management of grass tetany is therefore all about prevention. Prevention will begin with identifying and avoiding high risk pastures during calving and other risk periods, trying to maintain high legume content pastures, supplementary hay and the provision of Causemag as either a looselick, spread on hay or as lick blocks.
The most cost effective preventative strategy is the preparation of looslicks containing magnesium used in conjunction with hay. Below is a standard recipe for producing a looselick that can be made on-farm and fed out to mobs providing a daily supply of magnesium. The quantities in the recipe below should produce a total mix calculated to provide 200g/hd/day. Therefore the total mix for a mob with 100 cows would be 20 kg per day, or a batch of 140 kg per week. The levels of salt and molasses can be altered in order to increase or decrease intake levels.
Causemag – 30% / Salt – 30% / Lime – 20% / Molasses – 20% a Providing 200g of total mix per head per day.
For more information on Grass Tetany Prevention and Treatment feel free to call HVC on (02) 60362374.