Nitrate-nitrite toxicosis associated with duckweed (Portulaca Oleracea L.) (Portulacaceae) consumption in a herd of sheep in Kenya

Abstract

Background: Nitrate-nitrite toxicosis associated with the consumption of duckweed (Portulaca oleracea L.) (Portulacaceae) was diagnosed in a small herd comprising of 11 sheep in Korayo Sub Location, Rangwe Sub County of Homabay County in Kenya. Methods: The clinical signs were dyspnea, froth from the mouth, labored breathing, incoordination, tachycardia, increased urination, neck, fore and hind limb distension, aggressive movements, bloat, convulsions, and coma, before death. Results: All the 11 sheep died of intoxication before institution of therapy. Brownish mucous membranes and chocolate colored and poorly clotted blood were the significant necropsy observations. Mild pulmonary edema was characterized by the presence of limited froth in the trachea and bronchioles. At postmortem, the liver of the sheep was grossly congested, and the cardiac pericardium was inflamed. There was gastritis, enlarged, and congested kidneys with pin-point hemorrhages. Diphenylamine tests carried out on the fed duckweed and on ruminal duckweed contents were positive for nitrates. Duckweed (Portulaca oleracea) fed on sheep had 7.4% nitrate on dry matter basis (DM), whereas ruminal contents had 5.38% nitrate on DM basis. Chocolate-colored blood collected during postmortem had a methemoglobin fraction of 86%. Nitrate levels in pastures of 0.5% and above have been shown to be potentially dangerous, with acute poisoning likely to occur at times when the levels are above 1%. Death in sheep can occur when blood methemoglobin levels are in the range of 67%–90%. Conclusion: The observations from the present study are indicative of death in a herd of sheep due to nitrate-nitrite poisoning associated with the consumption of duckweed (Portulaca oleracea).