Harrowing is a pretty convenient way to deal with all that horse dung. It’s likely your equine friends are each leaving 15 or more deposits in your paddock each day and no horse owner needs telling that it builds up at an unholy rate.
Unfortunately, the humble harrow is generally part of the worm problem, not the solution.
Harrowing smashes up the dung and distributes it evenly about the paddock. Unfortunately, it distributes the parasites equally well.
In very hot climates, the breaking up of dung in this way can prove effective. It exposes eggs and larvae to the fierce heat and sun which can kill them. But in a country such as New Zealand, with its temperate and sub-tropical climate, the summers may not be hot enough to do the job.
If you feel that harrowing is the only viable solution to your “dung burden”, then do it on the hottest and sunniest day your local weather can muster.
Keep the horses off the paddock for at least three weeks – longer if you can manage it – to give the warm weather an opportunity to kill off as many larvae as possible (remember, infective strongyle larvae can only survive in pasture for a few weeks in warm and dry weather).
Never harrow a paddock when horses are still in it.
Harrowing is an even worse strategy in the cooler months as the strongyle larvae will be able to survive for several months, and, thanks to your harrowing, will be evenly distributed about the paddock waiting to infect horses.
In terms of parasite control, the best course is picking up the dung and composting it. A well maintained compost heat should generate enough heat for long enough to kill parasite eggs and larvae.
Normal composting temperatures are well above those needed to deal with your arch nemesis, strongyle larvae.
Composting is not just about heaping your collected dung in an unsightly pile. A few simple steps will ensure a healthy, odour-free compost heap that produces great material to return to your garden or even pasture. (See Composting your horse dung)
Picking up dung helps by removing the dung containing the eggs and larvae from the pasture. Getting it off when it’s fresh is best – wait no more than three days – as some larvae while wriggle their way from the dung and take up residence in the soil.
Horses are averse to eating grass near their droppings, so picking up the manure will also ultimately improve the percentage of a paddock where horses are happy to graze.
Your dung-removal programme will be even more effective if you can manage to pick it up before falls of rain, which help larvae move from dung piles into the soil or on to forage. Birds that tear apart dung pile in search of partly digested grain are also playing a part in egg and larvae distribution.
There is also a benefit in being able to shut up pastures for a time over the warmer months, when the metabolism of infective strongyle larvae will be using up their stored energy. Once they used it up, they die. If you’ve got the acreage and the time, it’s a sensible strategy.
Given that strongyles can hold out for only a few weeks in warmer weather, you can sensibly employ this strategy with your hay paddock.
Horse owners that graze cattle and sheep have another weapon in their arsenal.
Parasites are adapted to their target species, so for a cow or sheep to eat the infective larvae that affect horses is a death sentence for the parasite. Horses, of course, return the favour to sheep and cattle as they graze the same pasture.
This is particularly effective against strongyles, but you can employ a couple of extra strategies for maximum effect.
It is wise to leave the pasture unoccupied for a couple of weeks while the eggs mature (the time varies, depending upon the ambient temperature). After a couple of weeks of favourable weather, the grass will have come away and infective strongyle larvae will be parked on the grass waiting by the ingested. At this point you introduce the cattle or sheep, who will ingest them and kill them.
The larvae will continue to emerge and the cattle and sheep will continue to eat them, so graze the paddock for as long as possible.
If possible, use mature stock for this clean-up work, as they are far less likely to carry a heavy burden of Trichostrongylus, a parasite capable of infecting horse, sheep and cattle.
Once again, any strategies that reduce the number of infective larvae in a pasture will affect the re-infection rate of horses.
It is also advisable to feed horses off the ground, using buckets for hard-feed and hay nets or hay feeders for forage. The more a horse eats off the ground, the less its exposure to ground-based larvae.
» Next: What about the weather?
First published on Horsetalk.co.nz in February, 2009