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Is Harrowing and Spreading Manure on the Pasture Safe?

In the Netherlands, it is rarely dry or cold enough for long periods to completely kill larvae. Worm larvae do not survive well in high temperatures combined with drought, or during prolonged frost. Harrowing is only effective if followed by an extended period of dry or freezing weather.

Our advice:

  • Reduce risk by removing manure piles from the pasture.
  • If removal isn’t possible, leave the manure where it is—do not spread it.
  • Harrowing without the right weather conditions increases infection risk.

When is harrowing an option?

  • If the pasture is used for hay production.
  • If the land will not be grazed by horses for a long time.
  • If regular manure testing shows very low infection pressure.

When can horses return to the pasture after harrowing?
This strongly depends on the weather.
Severe winter frost or very hot summers help kill larvae, making it safer to return horses to the land.
However, caution remains necessary: a pasture can stay infectious for up to six months.

Spreading manure: when is it okay, and when not?
Spreading horse manure always carries a risk. Contaminated manure distributes larvae across the pasture, raising the infection pressure.

When might it be acceptable?

  • Preferably never—unless the manure is fully decomposed or composted.
  • In winter, if the pasture won’t be used for at least six months.
  • If all horses on the land have tested negative year-round and no new horses are introduced. Still, risk remains.

What makes manure safe?
Manure that has been heaped over summer can be safe. The internal temperature can rise to 60°C due to fermentation. At 50°C, all parasite stages die within one hour.

Note: The outer edges of the manure pile often do not reach these temperatures!

Summary

  • Harrowing is only responsible when followed by a long dry or frosty period. In the Netherlands, it is safer to remove manure directly—or leave it in place if removal is not possible.
  • Spreading manure is only advisable if it is fully composted, such as after a summer in a heap.

Weather conditions in the Netherlands are unpredictable. Recent years show increasingly warm winters and wet springs, raising the infection risk.

Want a safe pasture?

  • Remove manure as much as possible.
  • Do regular manure testing to monitor infection pressure.
  • Treat your horse in time when needed.

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