Prophylactic effect of l-cysteine on nitrate-induced alterations in respiratory exchange and metabolic rate in sheep

Abstract

Four rumen-fistulated wethers were individually caged and used in a 4 × 4 Latin square designed study. l-cysteine (0.21 g sulphur equivalent kg −0.75 body weight) and/or nitrate (1.3g NaNO 3kg −0.75 body weight) were administered into the rumen as a single dose 30 min after the morning meal of grass hay (27 g DM kg −0.75 body weight). Physiological saline was administered as the control treatment. In each period, oxygen consumption, carbon dioxide and methane production and metabolic rate were monitored by an open-circuit respiratory system. The administration of nitrate alone resulted in a marked accumulation of ruminal nitrite and then induced almost 20% methaemoglobin in total haemoglobin. Consequently, reductions in oxygen consumption, carbon dioxide production and metabolic rate were shown as well as a very marked reduction in methane production. The simultatneous administration of l-cysteine with nitrate suppressed nitrite production in the rumen and methaemoglobin formation, and consequently higher rates of the gas exchange and metabolism were observed. l-cysteine, or a treatment utilizing a similar effector mechanism, has prophylactic potential against nitrate poisoning in ruminant species.