Staggers

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.

Symptoms

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.

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

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).

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.