With cooler mornings on the up, sunshine on the down, and a flush of spring grass growth not far off – nitrate poisoning presents a real risk for our Waikato dairy herds – especially where new grass or winter crops are in the mix. The classic “nitrate weather” can catch the most experienced farmers off guard.

What causes nitrate poisoning anyway? Under certain conditions e.g., overcast days, cold spells, drought, flooding, or heavy fertilizer application – the plants including new annual grasses, turnips, and kale will build up nitrogen as the plant is unable to convert the nitrogen into protein under stress or rapid growth. If a cow eats too much high-nitrate feed, the nitrate interferes with the blood’s ability to carry oxygen. Essentially, it replaces the oxygen in the blood and the result can be fatal.

Cows affected by nitrate toxicity usually start to show symptoms 3 to 4 hours after grazing. Signs to watch out for include:

• Lethargic, wobbly, or weak.
• Rapid, open mouth breathing.
• Brown or bluish gums.
• Down or bloated.
• Sudden death.

If you see any of these signs, call your vet clinic immediately – time is of the essence for administering the antidote: methylene blue.

While you’re waiting for the vet, quickly but quietly remove animals off the suspected problem area. Leave down cows where they are to be treated as moving them could worsen their condition, but it’s recommended to have the herd handy to handling facilities – that way your vet can easily triage the mild or subclinical cases. It’s possible that after a nitrate toxicity you’ll see abortions as the nitrate blood will unfortunately affect the calf too.

Thankfully, it’s not all doom and gloom and it’s preventable by following these risk mitigating steps:

• Nitrate test your paddocks in the morning – take a sample from both the stalk and leaf as they can be different. A quick and cost-effective kit are available from all Anexa clinics.
• Manage grazing by:
  • Fill them up with other feed first (e.g., hay or silage) before offering high risk feed.
  • Limit time to 1-2 hours on a high-risk break.
  • Feed high risk paddocks in the afternoon as the sunlight helps to reduce nitrate. Nitrates are at their highest first thing in the morning.
• Stay alert and observe cattle closely for 3-4 hours after feeding.

Nitrate poisoning is a seasonal risk that can sneak up on the best-run farms. So, if you’re feeding winter crops or grazing recently fertilised paddocks, it’s worth taking a few extra precautions – and a quick nitrate test goes a long way. Have a chat with your vet if you’d like to discuss it further or receive tailored advice to your farm.

When the season is getting late, remember to:

Note the conditions (e.g., high-risk weather).

Immediate action if you see any warning signs.

Test your paddocks.

Reduce hunger – offer feed first.

Afternoon is the safest time of day.

Time on – no more than 1-2 hours on a high-risk break.

Eyes on – keep careful watch of your cows.