Temperature and pH effects on the oxygen equilibrium curve of the thoroughbred horse.

This study defined a new oxygen equilibrium curve for Thoroughbred horses under specific conditions. It was found that their standard P50 (a measure of oxygen affinity) is significantly lower than that of Hanoverian horses. The research also looked at how pH, temperature, and PCO2 affected this curve under exercise conditions.

Defining a New Oxygen Equilibrium Curve for Thoroughbred Horses

• The researchers in this study set out to define a new oxygen equilibrium curve for Thoroughbred horses. This curve, which essentially describes how well oxygen binds to hemoglobin in the blood, was determined under standard conditions of 37 degrees Celsius, a pH of 7.4, and a PCO2 (partial pressure of carbon dioxide) of 5.33 kPa.
• The standard P50 – a common measure of the oxygen affinity of hemoglobin – for Thoroughbred horses was found to be 2.83 +/- 0.04 kPa, which is notably lower than the P50 for Hanoverian horses (3.17 +/- 0.03 kPa) as determined by Clerbaux et al. in their study in 1986. This also turned out to be lower than other recorded values for horses in existing literature.

Examining the Impact of pH, Temperature, and PCO2 on the Oxygen Equilibrium Curve

• To further understand the implications of this new oxygen equilibrium curve for Thoroughbred horses, the researchers simulated intense exercise conditions and noted the individual impacts of pH, temperature, and PCO2 on the curve.
• The Bohr coefficient – a parameter depicting how blood pH affects the affinity of hemoglobin for oxygen – was found to be similar to that in humans (-0.41), implying that a drop in pH would result in hemoglobin releasing more oxygen.
• The temperature coefficient however, determined at 0.019, was lower than that for humans. This implies that the affinity of hemoglobin for oxygen in Thoroughbred horses is less susceptible to alterations in temperature.
• The researchers also demonstrated that these coefficients were dependent on saturation, implying that they could vary depending on the oxygen saturation level of the blood.