After a drought, fresh green pasture might seem like a blessing. But for livestock, it can pose a serious risk. Many animals have died after grazing on lush regrowth that contains high levels of nitrate. Understanding the risk and how to manage it could save your stock and prevent unnecessary losses.

Why Nitrate Levels Rise

During a drought, nitrate builds up in the soil. There is less uptake by pasture plants, no leaching from rain, and organic matter continues to break down, releasing nitrogen. Once the drought breaks and rain returns, plants absorb this nitrate rapidly. This is especially true during the first week after rainfall.

Crops such as autumn-sown ryegrass, greenfeed cereals, millet, sorghum, kale, rape, and maize can be particularly high in nitrate. Old pastures can be risky too, especially if they were heavily fertilised or contain nitrate-accumulating weeds like redroot.

Which Animals Are at Risk?

Cattle are the most sensitive to nitrate poisoning, followed by deer, goats, and sheep. Hungry stock grazing fresh regrowth are especially vulnerable. Deaths have occurred within hours of animals being moved onto a toxic paddock.

How Poisoning Happens

Nitrate itself is not highly toxic. The danger comes when it is converted into nitrite inside the rumen. Nitrite affects the blood’s ability to carry oxygen. Poisoned animals may appear drunk or sleepy. They often stagger, lie down, and deteriorate rapidly. Many are found dead with few signs of struggle.

How to Reduce the Risk

• Test your pasture or crop. If you don’t have a nitrate test kit, take samples to your vet clinic. Most provide same-day results.

• Feed hay or silage first. This reduces the amount of fresh pasture eaten on an empty stomach.

• Graze at the right time. Nitrate levels are highest at night and in the early morning. Wait until late morning or afternoon before putting stock onto suspect pasture.

• Limit initial grazing. Start with short grazing sessions. For example, allow only 15 minutes on new grass or lush crops to give the digestive system time to adapt.

• Provide shelter and reduce stress. Stress increases nitrate uptake. Ensure animals have access to shelter and are not overcrowded.

• Watch for signs. If animals look drowsy, are staggering, or lie down unexpectedly, seek immediate veterinary help. The antidote is methylene blue, but it must be given quickly.

Real-World Example

In one confirmed case, 17 cattle died after being moved into a paddock previously used for squash production. The crop had failed, and weeds had taken over, including large amounts of redroot. The nitrate levels in those plants proved fatal.

If You're New to Livestock

Managing pasture risks can be daunting, especially after dry weather. If you're new to farming or unsure about your setup, our What You Need to Know to Keep Livestock course covers practical pasture management, livestock nutrition, and how to prevent avoidable animal health issues. It’s designed for small block owners who want to get it right.