Understanding Horse Worming and Pasture Management

Why Blanket Worming Is No Longer Best Practice

For decades, the default approach on many yards was simple: every horse, every eight to twelve weeks, same tube of wormer. It was easy, it felt thorough, and it quietly created a problem. Worms that survive treatment pass on their resistance to the next generation, and in the UK we now have small redworm populations on some yards that shrug off entire drug families. Once that resistance is established in your paddock, you cannot undo it. You can only slow it down.

The good news is that a more thoughtful routine is also a cheaper one. Most adult horses in low-risk management carry very few worms and do not need frequent treatment. By testing first, you treat the horses that genuinely need it and leave the rest alone — which keeps those drugs working for the day you really do need them.

Start With a Faecal Egg Count

A faecal egg count, or FEC, tells you how many strongyle eggs your horse is shedding per gram of dung. It is a simple, inexpensive test, and most veterinary practices and equine laboratories will run one if you post fresh samples in a sealed bag. Collect from a fresh dropping, ideally still warm, from at least two or three different piles for accuracy, and label everything clearly if you are testing a whole yard.

Results are usually given in eggs per gram (epg), and a rough guide looks like this:

• Under 200 epg — low shedder. No treatment needed; retest in three to four months.
• 200 to 500 epg — moderate. Discuss with your vet whether treatment is warranted.
• Over 500 epg — high shedder. Treat, then retest ten to fourteen days later to confirm the wormer worked.

Roughly two-thirds of adult horses are naturally low shedders, and those are the ones you can safely leave untreated. Youngstock, elderly horses, and any horse with a compromised immune system need closer attention, and your vet may advise a slightly different protocol.

What an FEC Cannot Tell You

An egg count is a snapshot, not a full picture. It does not detect tapeworm, and it will not pick up encysted small redworm larvae, which bury themselves in the gut wall during autumn and winter and cause the most serious disease. Those larvae are not laying eggs, so they are invisible on a count.

For tapeworm, you need either a specific saliva or blood test, or a targeted treatment in late autumn and again in spring if your horse is at risk. For encysted redworm, most horses benefit from a single moxidectin-based treatment in late autumn or early winter, ideally after the first frost. Ask your vet to build this into your plan rather than guessing — it is the one part of the year where a strategic treatment still earns its place.

Pasture Management Does the Heavy Lifting

Worming is only half the job. The other half is reducing how many infective larvae your horse meets while grazing, and that comes down to routine field management.

• Poo pick at least twice a week in spring and summer, and no less than weekly the rest of the year. Removing dung before eggs hatch is the single most effective thing you can do.
• Harrow only in hot, dry weather — a sunny day above about 20°C will kill larvae on the surface within a few hours. Harrowing in cool, damp conditions just spreads the problem around.
• Rest paddocks for at least six to eight weeks in summer, longer in spring and autumn when larvae survive better.
• Cross-graze with sheep or cattle if you can. Their worms cannot infect horses, and they will nibble pasture down evenly.

Strategic Grazing That Works With the Weather

Larval numbers on pasture follow a predictable rhythm. They peak in late summer and autumn, when warmth and moisture suit them, and drop in a hard frost and through a hot, dry spell. Plan your grazing around that pattern.

Rotating between several smaller paddocks is far better than one large field, because you can rest each one properly. If you have limited land, consider strip grazing with a temporary fence, moving the line back daily so horses graze clean ground and dung accumulates behind them. Avoid overstocking — the guideline is roughly one to one and a half acres per horse for year-round grazing, more if the land is heavy clay or poorly drained.

Keep a small, well-drained area for high-risk times: wet winters, laminitis-prone horses, or any horse recovering from illness. Mud and standing water are where worms and bacteria thrive.

Keeping Records and Knowing Your Land

Write down every FEC result, every treatment, and the date, along with which paddock the horse was on. Patterns emerge quickly — you will spot which horse is your persistent high shedder and which fields consistently produce higher counts.

If you are new to a yard, or you have taken on a smallholding with horse paddocks, ask the previous owner for their worming history and get a baseline FEC on every horse before you treat anything. It is a small investment of time that sets you up for years of sensible, low-chemical management.

The aim is not to eliminate worms — that is impossible, and a little exposure actually helps horses build natural immunity. The aim is a manageable burden, healthy pasture, and a worming routine that still works when you need it most.