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Ryegrass Staggers in Calves

Ryegrass staggers (RGS) is one of the most common neurological diseases of cattle and may affect cattle of any age. The disease is more common in the North Island compared with the South Island. Cattle are not the only species affected; RGS may be seen in sheep, deer, horses and camelids.

RGS is caused by toxins produced by the endophytic fungus Neotyphodium lolli which lives in perennial ryegrass. The fungus produces toxins which provide the plant with insect repellent. One of the toxins produced is called lolitrem B; this is toxic in high concentrations to stock and is responsible for  causing loss of appetite and uncoordinated movement. The effects of lolitrem B are usually reversible as the toxin does not appear to cause long term damage to the central nervous system. Clinical signs usually begin to resolve once animals are taken off the affected grass.

The disease is less common in dairy cattle as they change pasture more often and tend to not graze the grass as close to its base. However, if an outbreak does occur it may cause significant financial impact.

Lolitrem B is present in ryegrass at all times of the year; however outbreaks usually occur between January and March when feed supply is short. Outbreaks can also occur in spring as the ryegrass flower can also have high endophyte concentrations. Clinical signs of ryegrass staggers usually develop with 7-14 days of being moved onto affected pastures. The number of affected animals is often high but  deaths are uncommon and usually associated with falling and not being able to get up leading to dehydration or even drowning. Death is not commonly due to Lolitrem B itself. Some cattle may present unexplained traumatic injuries.

Staggers can have farm management implications as it can be difficult to move stock, especially when animals need to be run through races for routine treatments like drenching. Even when no visible signs of ryegrass staggers are present, research suggest that it may affect stock growth and milk production.

When animals are undisturbed, there may be no obvious clinical signs present. It is only when animals are made to walk or run that clinical signs become evident. These may include:

  1. Head tremors and muscle twitching

  2. Head nodding and jerky limb movements

  3. Swaying and staggering, short bouncy steps

  4. Severe cases may collapse with splayed hindlimbs

If collapsed animals are left (without being stressed), in time they will usually stand and walk away. Heat stress can make clinical signs worse.

There is no specific treatment for ryegrass staggers but if animals are moved to “safe” pasture they usually recover within 1-2 weeks. Cattle may be fed other supplements to reduce the intake of affected pasture or moved to known safe pastures. The main risks with moving affected animals are that they injure themselves. Therefore affected dairy cows should be put on once daily milking or dried off. Anecdotal evidence suggests that some animals may benefit from a subcutaneous magnesium injection.

Control is based on effective pasture management; preventing overgrazing and avoiding build up of dead litter at the pasture base.  There are endophyte free ryegrasses and “safe” ryegrass species (has endophytes that don’t produce neurotoxins) available. These are not suited to whole farm use and require special management.

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