Of cows and sweet potatoes

The sweet potato Ipomoea batatas has been used throughout the world as a food source for hundreds of years. Byproducts used as animal feed as a result of sweet potato processing include cannery wastes and sweet potatoes culled during the packing process due to damage, off size or oversupply.

The Veterinary Record [1,2] and the Guardian [3] recently discussed an incident in which six cows died as a result of consuming sweet potatoes. As far as is known this is the first recorded case of sweet potato poisoning in animals in the country. Five days before the first death, the cows had been fed 7 kg sweet potatoes per head per day. The sweet potatoes used were considered unfit for human consumption due to bruising. Examination of the remaining tubers showed the presence of the fungus Fusarium solani, amongst other species, on the skins and broken surfaces. The cows died over a period of four days, following signs of rapidly progressive dyspnoea. The deaths occurred within hours of the first respiratory symptoms. Necropsy examination showed severe interstitial pneumonia with extensive interlobular emphysema. On the basis of the evidence gathered, ipomeanol toxicity due to consumption of mould-damaged sweet potatoes was believed to be responsible for the deaths of the cows [4].

Over the years, reports from the USA, Japan, Australia and Brazil have implicated sweet potatoes in the deaths of cattle from a pulmonary disease known variously as pulmonary oedema, pulmonary adenomatosis, acute bovine pulmonary emphysema and atypical interstitial pneumonia as a result of eating mould-damaged sweet potatoes. The sweet potato is one of several plants able to form stress metabolites (also referred to as abnormal metabolites or phytoalexins) when subjected to an injurious stimulus which could take the form of mechanical injury, insect invasion, exogenous chemicals and microbial pathogens such as fungi. Several species of fungi, including F. solani and Ceratocystis fimbriata, have been found to stimulate the sweet potato to produce toxins. These toxins, 3-substituted furans, are hepatotoxins and pulmonary toxins, and are products of the sweet potato tissue, rather than of the fungus. The pulmonary toxins can cause lesions in the lung tissue of cattle, rats, rabbits and guinea pigs. These pneumotoxins, referred to as lung oedema factors include 1-ipomeanol, 4-ipomeanol, 1,4-ipomeanol, 1,4-ipomeadiol and ipomeanine, and are responsible for the acute pulmonary oedema and emphysema observed following consumption of Fusarium-infected sweet potatoes. Although the toxicity of damaged sweet potatoes is well-documented in cattle, a case of pigs dying from sweet potato poisoning has also been reported in Papua New Guinea [5]. Th effects of these sweet potato toxins on humans are not known; there is at present growing interest in the use of 4-ipomeanol as a potential prodrug for P450-directed gene therapy of liver and brain cancers.

There have been no reported cases to date of acute human poisoning following the consumption of sweet potatoes containing either hepatotoxins or lung toxins. Nevertheless, it is important to only select undamaged sweet potatoes for both human and animal feeding. Some reports suggest that neither baking nor boiling eliminates the toxins. Every effort, should, however, be made to maintain conditions to prevent these toxic metabolites from forming in the first place.

References
[1] Ipomeanol poisoning in cattle fed sweet potatoes. Veterinary Record (2007) 161:771-774.
[2] Mawhinney I, Woodgear N, Trickey S, Payne J. Suspected sweet potato poisoning in cattle in the UK. Veterinary Record (2008) 162 (2):62-63.
[3] Meikle, J. Six cows killed by sweet potato poisoning. The Guardian (Tuesday January 15, 2008). Accessed 21 January 2008. http://lifeandhealth.guardian.co.uk/food/story/0,,2240987,00.html
[4] Veterinary Laboratories Agency Monthly Surveillance Report October 2007. Accessed 21 January 2008. http://www.defra.gov.uk/corporate/vla/science/documents/end-survreport-1007.pdf
[5] Low SG, Grant IM, Rodoni B, Bryden WL. Sweet potato (Ipomoea batatas) poisoning of pigs in Papua New Guinea. New Zealand Veterinary Journal (1993) 41 (4): 218.

Suggested reading
Poore MH, Rogers GM, Ferko-Cotten BL, Schultheis JR. 2000. Sweet potatoes and associated byproducts as feeds for beef cattle. In Food waste to animal feed. Westendorf MC (ed), Iowa State University Press, Ames, Iowa, USA, pp. 163-183.
Wilson BJ, Burka LT. 1983. Sweet potato toxins and related toxic furans. In Handbook of natural toxins. Volume 1. Plant and fungal toxins. Keeler RF, Tu AT (eds), Marcel Dekker, New York, USA, pp. 3-41.
Woolfe, JA. 1992. Sweet potato: an untapped food resource. Cambridge University Press, UK, 659 p.

To search the VetMed Resource database for records on sweet potato poisoning use the terms (poisoning:de and sweet potatoes:de)

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s