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Magnesium and grass staggers Preventing Mg deficiency Ryegrass staggers Ryegrass staggers symptoms Preventing ryegrass staggers Managing stock with ryegrass

There are two types of staggers, these are grass staggers and ryegrass staggers. Grass staggers is a metabolic disease in cows caused by a magnesium deficiency. By giving cows extra magnesium in their diet, you can prevent health issues like grass staggers and milk fever, which can help increase milk production. It's important to discuss with a vet before starting because there have been cases of salmonella infections linked to magnesium supplementation. Ryegrass staggers is a nervous disorder in cows caused by high levels of certain chemicals in pasture. You can manage this with specific diet and grazing practices.


Magnesium and grass staggers (grass tetany)

Grass staggers is a metabolic disease caused by magnesium deficiency. It is also called hypomagnesaemia. The cow is dependent on the amount of magnesium supplied in her diet, and from supplements.

Supplementing cows with extra magnesium (Mg) in late pregnancy and early lactation has become routine on most farms since the 1970’s. Mg supplementation helps prevent animal health problems, such as milk fever and grass staggers (tetany), and potentially increases milk production.

Mg plays an important role in nerve and muscle function and functioning of the immune system. Although cows have significant stores of Mg in the bones, little of these stores are available to maintain levels in the blood. Therefore, the cow is dependent on the Mg supplied in the diet and from supplements to maintain blood levels.  Blood and urine tests can confirm Mg deficiency. Consult your vet.

There have been reports from New Zealand and Australia of Salmonella infections occurring in dairy cows that had received Mg supplementation, delivered as granules, prills, pellets, powder and via the drinking water.

Before starting Mg supplementation for your dairy herd, consult your veterinarian to discuss the potential risks and to determine if there are any health or environmental factors that should be taken into consideration to reduce the risk of the development of Salmonellosis.


The initial symptoms of Mg deficiency are nervousness, ears pricked, nostrils flaring, eyes alert and head held high. Movement is stiff, like a cow is walking on stilts, and she will stagger when forced to move quickly. Cows suffer loss of appetite and reduced milk production.  Death results from a “tetany”, where the muscles contract uncontrollably, including the heart.

Preventing magnesium deficiency

It is recommended that dry cows receive a diet containing 0.35 percent Mg, and lactating cows 0.28 percent Mg.

There are a number of different sources of magnesium, and methods of adding these into a cow’s diet. Common methods include drenching, pasture dusting, hay slurries, through water, and as magnesium bolus. Each method has its own limitations and advantages, so it is up to each farm how they choose to supplement their magnesium.

Factors that increase Mg requirements of cows during the winter/spring period are:

  • Diets naturally low in Mg and/or high in potassium (K) e.g. pastures (low Mg or high K), maize silage or fodder beet (low Mg), paddocks with high potash or effluent (high K).
  • Cold wet weather in spring, depressing grass growth and cow intakes.
  • High cow demand for Mg over calving and early lactation, e.g. due to high milk production.

For more information, refer to the Farmfact below.

Table 1. Dietary magnesium concentrations and quantity of supplementary Mg required (grams/cow/day) for different types of dairy cattle.

Cow status Mg requirement(% of diet) Supplementary Mg (g/cow/day)
Jersey Crossbred Friesian
Dry 0.35% 12 16 20
Lactating 0.28% 15 17 20

Table 2. Quantities of magnesium sources to supply the required amounts of pure magnesium (down the cow's throat).

Magnesium source (% Mg) Example product Magnesium required (g/cow/day)
12 g 14 g 16 g 18 g 20 g
Mg Oxide (55%) CausMag 22 25 29 33 36
Mg Sulphate (10%) Epsom salts 122 142 162 182 202
Mg Chloride (12%) Mag chloride 100 117 134 151 167

Note: If dusting magnesium oxide on pasture, the quantities above need to be at least doubled, possibly tripled, to allow for field losses. When mixing with feed, double the rates above.

Table 3. Amount of magnesium oxide dusted on pasture (g/cow/day).

Magnesium source (% Mg) Rate Magnesium required (g/cow/day)
12 g 14 g 16 g 18 g 20 g
Mg Oxide (55%) Double rate 44 50 60 66 72
Triple rate 66 78 90 100 108

Ryegrass staggers

Ryegrass staggers is the nervous disorder animals suffer from as a result of eating pasture containing high levels of the ryegrass endophyte chemical Lolitrem B.

Ryegrass staggers symptoms

  • Tremors in the neck and head (early)
  • Heavy tremors and stiff legs (advanced)

Ryegrass staggers symptoms are most likely seen in stock which graze seed heads or graze into the base of the pasture where the endophyte chemical is concentrated. Symptoms start with tremors in the neck and head, followed by heavy tremors and stiff legs. Seriously affected animals often fall over when disturbed. Calves appear to be more susceptible to ryegrass staggers than older stock.

Outbreaks of Ryegrass staggers occur from late November until the end of April, but the problem is sporadic and tends to be worst from late January to early February. Animals are at most risk when a sustained hot, dry spell is followed by rain, especially when pastures are over grazed.

Wild-type endophytes in New Zealand perennial ryegrass pastures produce a toxin that causes ryegrass staggers. Over the past 20 years, new endophytes have become available that do not produce this toxin, while still protecting the plants from disease. Depending on the age of your pasture, and what was sown, will determine the risk of Ryegrass Staggers on your farm.

Preventing ryegrass staggers

Specific management will vary with the farm business goals, pasture type, season and locations. However, some general principles can be used.

The highest levels of endophyte toxins are in the ryegrass leaf sheath, seed head and seed. Management that increases the leaf content of ryegrass and reduces intake of seed head and plant parts near ground level will reduce the chance of ryegrass staggers.

This includes:

  • feeding a high quality supplement (silage, last season's hay, turnips, maize)
  • leaving higher post-grazing residuals
  • pasture topping or mowing of seed heads
  • grazing endophyte-free/low-endophyte/novel-endophyte ryegrass pastures if available (break feed if there is only a small area available)

Supplementary feeding with high quality pasture silage is the most practical way for most dairy farmers to manage ryegrass staggers by substituting supplement for pasture.

Managing stock with ryegrass staggers

Seriously affected stock should be:

  • managed separate from the main herd and milking frequency reduced to once a day
  • fed a high quality supplement (silage, last season's hay, turnips, maize) to reduce their intake of ryegrass
  • fed pasture of another species - tall fescue (not wild), annual ryegrasses, cocksfoot, lucerne, clover or chicory are excellent
  • moved slowly and left undisturbed as much as possible
  • not grazed in paddocks with hazards; ponds, ditches and bluffs

For badly affected calves consider a 100% supplement diet. Depending on calf weight, 4 kg dry matter per head will be required, some of which may need to be a high quality feed such as meal or brassica crops.

Last updated: Sep 2023
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