Franklin Vets Blog

Beware of nitrate toxicity

May 18, 2020

Finding or being called out to a paddock full of dead or dying cows is the emergency all farmers and vets fear. Unfortunately, we are now entering the high-risk period for nitrate toxicity so here is a quick refresher of what nitrate toxicity is, risk factors and how to minimise the risk of toxicity.

Nitrate is the main form of nitrogen taken up by plants from the soil and is usually quickly converted through several steps into plant proteins. However, if plants don’t have enough energy, this process slows down, and nitrate accumulates in the plant. When cattle eat nitrate, rumen bugs convert this into nitrite and then into ammonia or protein. If rumen bugs are overwhelmed by large amounts of nitrate, nitrite levels build up in the rumen and are absorbed into the blood where it affects the ability of haemoglobin in the blood to carry oxygen.Autumn grass

Within a few hours, cows may be seen open mouth breathing, drooling, showing signs of gut pain and diarrhoea, and then staggering and collapse. Death occurs rapidly. Many surviving animals often abort.

This is an emergency so call us straight away and move animals off the source of the toxin.

Risk factors for nitrate toxicity:

  • Plants regrowing after a period of stress (e.g. drought)
  • Rapidly growing immature plants (e.g. new grasses)
  • Low temperature (e.g. morning and evening)
  • Low light (e.g. overcast days)
  • High nitrogen fertiliser rates (peaks 10-14 days after application)
  • Hungry cows, especially after transport or other stress.

To minimise the risk of toxicity:

  • Test plants before feeding them. Either bring in a sample of the feed or you can purchase a test kit to test on farm. Avoid feeding high risk feeds and keep retesting until levels return to a safer level.
  • Ensure cattle are not hungry and have a full belly before going onto risky pasture.
  • Feed risky pasture late morning or early afternoon when the toxin levels are likely to be lowest.
  • Restrict grazing area and use double tapes for extra security and minimise access to less than an hour.
  • Check cows regularly after they have been on the feed as signs of toxicity typically occur 4 to 5 hours after they have eaten it.
  • Gradually introduce higher risk feeds to allow the rumen bugs time to adapt.
  • Be aware of what weeds are present on the farm and prevent access of cows to them. Hungry cows will eat plants that they would usually avoid.

If you would like more information, check out our nitrate toxicity video on our Farm Services Facebook page or give your local clinic a call.

Dr Ilyse Jennens BVSc (Dist) MANZCVS Medicine of Dairy Cattle, Branch Manager at Franklin Vets Waitakaruru