Potential management practices which may reduce the risk of grass sickness

Dr. Scott Pirie, Easter Bush Veterinary Centre, Easter Bush, Roslin, Midlothian EH25 9RG

Several studies have identified certain “risk factors” associated with an increased incidence of grass sickness and certain “protective factors” associated with a decreased incidence of grass sickness. These can be sub-divided into:

1. Horse-related factors

2. Premises-related factors

3. Management-related factors

Therefore following the occurrence of a case (or several cases), it may be worth considering which of these factors can be manipulated with a view to reducing the risk of the disease occurring in other horses. This may involve the implementation of “protective” factors and/or the avoidance of “risk” factors. Unfortunately, out of all the recognised “protective” and “risk” factors, there are only a few which can be manipulated by altering the day-to-day management of the “at-risk” horses.

Risk avoidance

• Minimise exposure to pastures where previous cases have occurred
• Minimise any pasture/soil disturbance (e.g. harrowing/mechanical faeces removal/pipe-laying/construction work etc.)
• Minimise soil exposure (e.g. close grazing/poaching of fields)
• Avoid any sudden changes in diet (quantity and/or feed type)
• Avoid the “over-use” of ivermectin-based wormers (e.g. rotate with other classes of wormers)

If circumstances dictate that the above changes have to be prioritised, then they should be prioritised towards stock which possess the greatest “horse-related risk factors” (young adults, new arrivals, horses in “show condition”) and at “peak” seasonal (spring and early summer) and climatic (cool/dry weather) periods.

Implementation of potential protective factors

• Co-graze with ruminants
• Regular grass cutting on pastures
• Hand removal of droppings
• Supplementary forage feeding (hay/haylage)

November 2005