The effect of colic on oxygen extraction in horses.

The research article evaluates how colic affects oxygen extraction in horses by testing blood samples and studying oxygen transport. It was observed that horses with severe colic had lower blood pH and higher oxygen extraction ratios compared to healthy horses.

Research Methodology

• The research was performed on horses with colic symptoms. The severity of colic was ranked on a scale of 1 to 3 using a gravity score (GS), with higher scores denoting more severe conditions. Healthy horses were used as control subjects.
• For the study, blood samples were collected from both the jugular vein and carotid artery of all tested horses.
• Various contents of the blood samples, such as 2,3-diphosphoglycerate, adenosine triphosphate, inorganic phosphate, and chloride concentrations, were then measured.
• pH levels (acidity or alkalinity measure) and partial pressures of carbon dioxide (PCO(2)) and oxygen (PO(2)) were also observed.
• Using the collected data, oxygen equilibrium curves (OEC) were developed under standard conditions, and the oxygen extraction ratios were then calculated.

Research Findings

• The results showed no difference in haemoglobin oxygen affinity, measured by P50(std), between healthy and colic-affected horses.
• Horses with the highest gravity score, i.e., GS=3, had lower blood pH compared to healthy horses, indicating that severe colic leads to increased blood acidity.
• Furthermore, arterial and venous partial pressures of oxygen at 50% haemoglobin saturation (P50(a) and P50(v)) were found to be significantly higher in horses suffering from severe colic (GS=3), compared to healthy horses. This suggests that colic increases the amount of pressure required to attain half-saturation of haemoglobin with oxygen, making it harder for oxygen to bind to haemoglobin in these horses.
• Oxygen extraction ratio, the proportion of oxygen removed from blood for tissue use, was also significantly increased in colic horses with a GS=3. This indicates a higher amount of oxygen was being used in these horses.

Conclusions

• The findings suggest that severe colic conditions can alter the blood’s physiological parameters, leading to increased oxygen pressure for haemoglobin saturation and an elevated oxygen extraction ratio.
• The increase in the oxygen extraction ratio in severely affected animals indicates that the body’s oxygen transport system compensates when systemic oxygen delivery decreases, which is an expected response in horses with severe colic.