Ergot Toxins: Hidden summer threat to cow health

These changes can negatively affect cow performance. Farmers often observe a subtle drop in dry-matter intake, along with a drop in milk production, with no obvious reason. Cows can become fidgety and touchy in the shed. These signs could be the first indicator of an increase in ergot toxin, a toxic fungus that takes hold in ryegrass seed heads during times of plant stress. Ergot doesn’t come with a warning sticker, but it can bring a host of problems.

<pWhat are ergot toxins?

Ergot is a fungus (Claviceps purpurea) that can infect grasses and cereals, particularly ryegrass. When it infects a seed head, it can replace the normal seed with a hard, dark body called a sclerotium. If cows eat ergotcontaminated pasture or conserved feed, ergot alkaloids can affect appetite, blood flow, hormones, and heat control. New Zealand cases have linked ergotcontaminated feed with serious illness. Deaths from ergot toxicity are rare, but when they occur they are sudden and can affect large numbers of animals with little warning.

Why the seed head matters

As ryegrass goes to seed, cows can take in more seed head material in each mouthful. That is when exposure can rise, especially if ergot bodies are present. While seed heads are a sign of grass maturity, they’re also a prompt to look closer.

A simple paddock check works well. When pasture is starting to seed, walk the paddock and inspect seed heads. If you can see dark, hard bodies in the seed head zone, treat that paddock as higher risk.

MPI has also warned that feed affected by ergot is not fit for purpose under the ACVM Act, and it should not be fed to animals.

Early signs you might see

Ergot does not always look dramatic at first. On many farms it shows up as performance going backwards.

• You may notice that cows are slower to graze, they pick around the pasture, or they do not clean out a paddock as they would normally.
• You may see milk yields flatten or dip even though feed looks fine and there is no obvious disease pressure.
• You may notice more cows standing near troughs or shade on mild days, because ergot can reduct blood flow to the skin and make heat control harder.

More serious signs can include swollen feet, increased lameness, or tissue damage to feet, tails, or lower legs in severe cases.

What it can look like in the paddock

If ergot is part of the picture, the pattern is often consistent across a mob and across breaks on the same paddock.

• Cows can be reluctant to get stuck into a fresh break.
• Milk response can drop without a clear feed shortage.
• Cows tend to stand around more, graze less, and spread out.

You can see changes earlier in the day than you would normally expect.

Ergot vs other ‘endophyte’ problems

Ergot can get lumped in with other pasture issues, so it helps to separate the likely culprits. Ryegrass staggers is linked to endophyte toxins like lolitrem B. It tends to show up as a ‘drunk’ gait, tremors, and coordination issues, worse when cows are moved or stressed. Ergot is different. The red flags are appetite and heat control first, then circulation problems in harder cases. You can have both problems occurring together, so don’t rely on one sign.

When risk lifts

Ergot pressure increases when there is humidity and heat. Under these conditions, grasses come under stress and start going to seed. The problem only gets worse when seed heads are present, especially if paddocks have been left longer, there is more stem, and cows are forced to graze tighter. It can also turn up in baleage, hay, or silage made from seeding pasture. Stock class matters. Lactating cows are less forgiving when intake drops, and pregnant animals are particularly at risk if blood flow is constricted.

If you suspect ergot, take photos of seed heads, keep a sample of the feed, and record which mob and paddock were involved. That gives your vet something to work with and helps you avoid repeating the same risk across the rotation.

What To Do Now

There is no antidote for ergot poisoning. The job is to avoid exposure early and get cows off suspect feed. Many cows improve once they are removed from the source.

• Start with a regular pasture check. If seed heads are forming, inspect them weekly.
• If you find ergot bodies, keep cows out of that paddock and talk with your vet or feed adviser about alternatives.
• Graze earlier where you can, before seed heads form.
• Top or clip paddocks before grazing if seed heads are present
• Use other paddocks, silage, or bought-in feed when the risk is high.
• Consider adding a mineral-based toxin binder to supplemental feed; these can be effective at binding the toxin.
• Check hay and silage sources, because conserved feed made from pasture containing seedheads can also carry ergot.
• Contact your vet straight away if you suspect ergot toxicity, especially if you see swelling, lameness, or tissue damage.
• If you keep one habit through late summer and autumn, make it this: When ryegrass starts to seed, take a close look at the seed head zone.