Summer is great for worm control in Australia - especially if the conditions are hot and dry.
For the major worm types that affect adult horses - the strongyles - warm weather helps the eggs & larvae in manure to develop quickly, but when they reach a certain stage of their development, hot, dry conditions cause the larvae to use up energy stores and they die of energy exhaustion and starvation.
What this means for the horse world is that larvae disappear rapidly from pastures during hot, dry weather, but they survive extremely well during our relatively mild winter months.
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Horses can pick up strongyle larvae through the normal process of grazing, as larvae crawl up blades of grass. A single early-morning dewdrop on a grass blade might reveal thousands of them. Horses can also ingest the larvae directly from the soil or from drinking contaminated water.
While we can't control the weather there are several other things we can do to help keep worms under control in our horses paddocks. Here's how to make the most of the hot weather:
- Don't overstock pastures. As a guide a ratio of two horses per hectare (1-1.5 acres per horse). Overstocking results in pasture with a high concentration of droppings and therefore great potential to re-infect, if manure contain worm eggs. Horses may also be forced to graze closer to droppings, which increases the risk of eating higher levels of worm larvae.
- Horse manure should not be used as a fertiliser for equine pastures due to the risk of spreading parasites.
- Ideally droppings should be removed from the pasture at least twice a week. This will help prevent the development of 'poo' areas and removes the source of new worm eggs.
- Where possible, divide grazing areas into smaller paddocks and rotate horses at regular intervals. To be effective, it is important that all horses grazing together are on the same worm control strategy (this does not necessarily mean that all horses are treated at the same time with the same product).
- Harrowing rested pasture can be useful in dry conditions only, as it exposes the larvae which dry out and die.
- In summer, allowing pasture to rest where possible aids worm control as the majority of larvae on the pasture will die-off.
- Once horses have been wormed it is best not to move them immediately to a new pasture.
- Rotate paddocks with cattle or sheep. These guys will happily eat grass that horses consider unpalatable (such as in poo areas) and in the process ingest equine worm larvae which will not survive in a cattle or sheep host.
These actions, together with a worming program that best suits your horse will go a long way to keeping your horse's worm burden under control.
Source: British Horse Society and Strongyles: The Worst of the Worms by Karen Briggs