Oxidative stress resulting from subclinical nitrite poisoning in cattle

Oxidative stress following prolonged exposure to nitrate has been implicated in inducing subclinical nitrite poisoning in dairy cattle herd, with poor health condition and reproductive disorders. Lipid peroxidation final product was measured by estimating thiobarbituric acid reactive substances (TBARS). Intrinsic antioxidants; glutathione (GSH), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase were measured. Nitrite in plasma, nitrate in grass and water was estimated. Methemoglobin (MetHb) concentration was also measured. TBARS were significantly higher and GSH was lower in nitrite exposed cattle. The activity of the antioxidant enzymes GSH-Px, SOD, and catalase were decreased in the subjects exposed to nitrite. Nitrite in plasma of affected cattle was significantly higher. Forage provided to affected cattle was rich in nitrate. Water used for the irrigation of suspected alfalfa grasses had high levels of nitrate, suggesting the source of nitrate contamination. Oxidative stress was evident in nitrite-affected animals as reflected by the increasing of lipid peroxidation products and the decline in the activities of the antioxidant enzymes and the depletion of reduced GSH. The present study provides indications that prolonged exposure to moderate amounts of nitrite would overwhelm the antioxidant system and lead to unseen oxidative damage manifested clinically by productive and reproductive disorders.