SMCO Poisoning

SMCO toxicity, also known as redwater or kale anaemia, is a very uncommon occurrence seen in animals grazing brassicas. SMCO (S-methyl cysteine sulphoxide) is in all brassicas in varying concentrations, especially kale. It is converted to the oxidative compound dimethyl sulphide which reacts with red blood cells and decreases haemoglobin, causing anaemia and red tinged urine. Animals must be on the toxic feed for at least one week for clinical signs to begin.

Clinical signs are weakness, diarrhea, yellow mucus membranes, poor performance, red urine and death.

SMCO concentrations increase in older plants and the flowering plant in spring. Levels are also higher on crops with high nitrogen and sulphate soil or fertilizer exposure. Ensiling affected crops does not stop the high SMCO concentration.

SMCO cannot be tested in the plant or the animal in NZ any more. Diagnosis requires proving the presence of severe anaemia and ruling out copper poisoning and bracken fern toxicity which cause similar clinical signs and anaemia. It is also important to rule out nitrate poisoning by testing suspect crops.

Once a toxic crop has been identified, ideally it would not be fed. However if toxic crops need to be utilized, animals can adapt to increased SMCO feeds to some extent with a sound transition regime over a 10 day period and feeding the toxic feed at no more than 50-60% of the diet. Very toxic crops would need to be fed at lower rates than this. If the crop needs to be fed, change breaks daily and ensure animals don’t go onto the crop empty. It takes the animal 4-8 weeks to replenish red blood cell levels so affected animals shouldn’t be stressed or run any distance during this time period. Treatment with selenium may reduce the oxidative effects of SMCO. Cows are suspected to be more susceptible to SMCO than sheep, however there are anecdotal reports of feeding known toxic crops to cows following sheep deaths without issue if they were carefully managed.

Although it is seldom reported, this winter period we have seen SMCO poisoning in sheep in the Maniototo on two farms feeding different brassica crops resulting in substantial losses and there are reports of other cases further afield. Bloat, acidosis, nitrate poisoning, scald and choke are more common and better known than SMCO toxicity, however it is important to keep it in mind when feeding brassicas to any ruminants.