The Subtropical Dairy program is warning farmers in northern drought-affected areas to be aware of the risks in feeding stressed or stunted sorghum crops to animals.
The warning also applies to feed hays made from these crops.
According to this Queensland Government website, cyanide (sometimes called prussic acid) and nitrate can be present in various amounts in grain and forage sorghums.
"In hot and dry conditions, such as drought, these plants become stressed, causing them to accumulate these toxins," it said.
"Fatalities can occur where ruminants graze sorghum crops or are fed sorghum hays containing excess levels of cyanide and or nitrate toxins."
Signs of cyanide poisoning in animals include: Rapid laboured breathing. Frothing at the mouth. Mucous membranes that are bright red in colour. Muscle weakness or twitching. Staggering. Convulsing. Unconsciousness. Death.
Signs of nitrate poisoning in livestock are similar to cyanide poisoning and include: Increased heart rate. Rapid laboured breathing. Muscle weakness or tremors. Blue-grey or brown mucous membranes. Frothing at the mouth. Abortion. Staggering gait. Unconsciousness. Death.
The website warns that animals eating large amounts of toxic feed die within 5–15 minutes of developing clinical signs of poisoning.
"Affected animals rarely survive more than 1–2 hours after consuming lethal quantities," it said.
Samples of suspect crops and hay can be sent to labs for testing before feeding out.
There is a 1-2 day turn-around-time for cyanide testing after the sample is received at the laboratory.
The cost of sample processing and testing is about $80 per plant sample.
The website said the following guidelines for using sorghum crops as fodder can help reduce the risk of cyanide and nitrate poisoning: Avoid grazing stressed plants or when regrowth is sprouting. Delay grazing until plants are more than 45cm high for short varieties and 75cm high for tall varieties. Flowering plants or grain are less likely to poison stock. Do not graze hungry stock. Animals are most likely to be poisoned if they eat large amounts in a short time. Watch stock closely in the first hour and monitor at least twice a day for the first few days. Supplement stock with sulphur-containing licks or blocks or molasses (which is naturally rich in sulphur). Sorghums are low in sulphur and sulphur helps the liver to detoxify cyanide. Test crops for cyanide and/or nitrate levels before using as fodder if in doubt about its safety. Do not use crops that are unsafe to graze to make hay. Ensiling hazardous sorghum will reduce the cyanide content but the end product should be tested before use.
More information about prussic acids and grazing affected crops can be found on this Queensland Government website this Queensland Government website and this NSW Primary Industries website .