The effect of nitrate supplementation on arterial blood gases, haemoglobin fractions and heart rate in Bos indicus cattle after exercise

Abstract

The objective of this study was to investigate the effects of nitrate treatment on the arterial blood gas and haemoglobin fractions from Bos indicus steers after exercise. Bos indicus steers (n = 12; mean bodyweight ± s.e.m., 397 kg ± 10.84 kg) were used in this experiment to investigate the effects of three dose rates of nitrate salts (0, 30 or 50 g of nitrate/day) on arterial blood gases, methaemoglobin concentration, carboxyhaemoglobin concentration, oxyhaemoglobin concentration, total haemoglobin concentration, haematocrit, heart rate, and respiratory rate after exercise. Increasing the dose rate of nitrate resulted in a decrease in the partial pressure of oxygen (P = 0.004) in blood. Steers treated with 50 g nitrate/day had a decrease in oxyhaemoglobin concentration (P = 0.001) and a concomitant increase in methaemoglobin (P = 0.001) and carboxyhaemoglobin (P = 0.001) compared with steers treated with 0 or 30 g nitrate/day. Steers dosed with 50 g of nitrate had greater heart rates immediately after the exercise regimen compared with the steers dosed with 30 g of nitrate (P = 0.043) or no nitrate (P = 0.018). There was no difference between treatments for respiratory rate (P = 0.673) or rectal temperature (P = 0.207) after the exercise regimen. Feeding nitrate to Bos indicus cattle results in a decrease in the oxygen carrying capacity of their blood. It is likely that doses of nitrate greater than 50 g per day for this class of animal could induce hypoxaemic trauma if cattle have exercise imposed after consuming a nitrate supplement.