Clinical signs, blood gases and acid–base balance after nitrate administration in calves

Abstract

This work is focused on the course and changes of selected clinical and laboratory findings after nitrate administration in seven calves. The calves were 3–6 months old, were fed a solid diet and had an average body weight of 97 kg. Nitrates were administered intraruminally in a water solution of KNO₃ at a dose of 0.5 g/kg of body weight. We observed the development and course of methaemoglobinaemia (% MtHb) in relation to the emergence of clinical findings, changes in body temperature, breathing and pulse rates, blood gases and acid–base balance. Various time trends as well as methaemoglobinaemia levels were recorded when values increased. The highest values of MtHb were found in the three youngest calves (67.5, 70.9 and 90.3 %), which were consequently treated by 1 % methylene blue solution because of marked clinical findings. Marked changes were observed in breathing and pulse rates, which correlated significantly with methaemoglobinaemia levels (P < 0.001). Significant effect of nitrate-induced methaemoglobinaemia was found on blood pH (P < 0.05), pO₂ (P < 0.001) and O₂ saturation (P < 0.01). Nitrate administration and formation of methaemoglobin did not affect the metabolic parameters of acid–base balance. Changing MtHb values correlated significantly positively with changes of blood pH (P < 0.01), breathing and pulse rates (P < 0.001) and negatively with pCO₂ (P < 0.05), pO₂ and O₂ saturation (P < 0.001). The obtained results indicate a markedly different development and course of nitrate poisoning. More distinct changes in clinical findings were not observed until the methaemoglobinaemia levels were over 60 %. Methaemoglobinaemia resulted in failure of oxygen transport and hypoxaemia with a significantly negative correlation of both parameters. The achieved results contribute to the study of acute nitrate/nitrite poisoning in cattle and supplement the present knowledge by significant correlation relationships between methaemoglobinaemia levels and some clinical signs and metabolic indices.