Using drought stressed corn as a forage alternative seems like a good way of utilising a stunted crop but staff at the South Dakota University Extension (SDSU) have warned that fodder this winter may contain higher nitrate levels, complicating cattle digestion, sometimes with fatal results.

Nitrate is found in all plants but sudangrass, pearlmillet, oats, orchardgrass and tall fescue can accumulate nitrate to high levels.

Toxic levels of accumulation are possible in red root pigweed, common lambsquarters, ragweed, velvetleaf, witchgrass, canada thistle and black nightshade.

Animals make protein from nitrates as plants do. This process is normal and requires rumen bacteria to convert nitrate into nitrite, which is then processed into ammonia.

When nitrate levels in the animal rumen become too high is when nitrate to nitrite conversion is faster than nitrite to ammonia conversion. According to SDSU experts, this is when the animal’s system becomes overwhelmed.

Health risks stem from nitrite accumulating in the bloodstream, where it reacts with haemoglobin, the oxygen carrying molecule. This derives methemoglobin which cannot transport oxygen causing internal suffocation of the animal.

This causes breathing difficulties, a drop in body temperature, violent heartbeat fluctuations and loss of muscular coordination. Reproduction ability can be affected at low nitrate levels.

Following the onset of these symptoms the animal can be dead within three to four hours and the SDSU team has advised Nitrate Poisoning is worse in cattle than sheep and horses.

Furthermore, toxicity levels are affected by the rate the nitrate is consumed. SDSU experts have said that around twice as much nitrate is required to kill a ruminant when nitrate is eaten in forage as when it is consumed quickly as in a supplement or accidental consumption of nitrate fertiliser.

Due to nitrogen spillages being palatable to cattle this represents a realistic danger on farms.

However, the extension team added that the health and condition of an animal effects nitrate digestion ability and, therefore, the level at which the substance becomes toxic.

When cattle are ill or have faced an abrupt diet change because toxic nitrate ion intake varies from 30 to 45 grams per 100 pounds of bodyweight for a healthy animal and as little as eight to 22 grams.

Understanding forage contents is, therefore, vital. SDSU experts have advised that chemical analysis of forage can also assess energy high protein and low energy levels that are common problems in drought stressed forage.