Age related decreases in thermoregulation and cardiovascular function in horses.

The research reveals that older horses might be more prone to heat-related challenges, possibly due to compromised cardiovascular functions and reduced plasma volume, which seem to affect their ability to balance exercise and body temperature regulation.

Methodology

The study was divided into two parts.

• In the first part, 11 Standardbred mares, 6 young (average 7.7 years) and 5 older ones (average 26 years), were run on a treadmill set with specifications to ensure an even work rate of 1625 watts until their core temperature hit 40 degrees Celsius. Throughout the process and up to 10 minutes after stopping, their core, skin, and rectal temperature, along with heart rates, were recorded per minute. The subjects’ blood samples were collected pre and post exercise at 40 degrees Celsius and every 5 minutes up to 10 minutes to measure packed cell volume, lactate, and plasma protein. Sweat loss was estimated via body weight.
• In the second part of the study, plasma volume was gauged in 26 young (average 8.2 years) and 8 older horses (average 26.6 years) using Evans Blue dye. Red cell volume and blood volume before exercise were calculated with the help of these plasma volume readings and packed cell volume.

Results

Research findings highlighted several key differences between young and older horses.

• Older horses quicker reached preferred core temperature (40 degrees Celsius), had a higher heart rate when they hit that temperature, and had higher sweat losses—all of which imply they exerted themselves more.
• Heart rates after exercise were not significantly different between young and old horses indicating similar recovery times.
• There were no significant age-related differences in core, skin, and rectal temperatures before and after exercise, lactate levels, packed cell volume, or plasma protein, which means that age did not affect these particular variables.
• They found higher plasma volume and pre-exercise blood and red cell volume in younger horses as compared to older ones.

Conclusion

Merging the findings from both studies showed that ageing could reduce a horse’s ability to manage simultaneous demands of exercise and body temperature regulation, partly due to a decrease in pre-exercise plasma volume. This understanding could guide the management of physical exertion in older horses.