Movement asymmetry was triggered in Icelandic horses that got heavier and put on fat, researchers report.
The animals in the study, all geldings, also showed evidence of reduced fitness, and their performance was assessed as poorer in a breed evaluation field test by judges.
The study by Anna Jansson and her fellow researchers, reported in the journal Physiological Reports, set out to examine the effect of altered body weight and body fat content on exercise performance and recovery.
Nine Icelandic horses were split into two groups, and changes in body weight and fat content were induced by feeding a high or restricted energy allowance for 36 days in a cross-over design.
In the last week of each treatment, body weight and body condition score were recorded, and their body fat percentage was estimated using ultrasound. Each horse was then given a standardized treadmill exercise test and a competition-like field test, which was scored by judges.
Blood samples were collected, and heart rate (HR), rectal temperature (RT), and respiratory rate (RR) were also recorded.
Objective locomotion analyses were performed before and after the field test.
The researchers, with the Swedish University of Agricultural Sciences and Hólar University in Iceland, found that the higher energy diet achieved its aim: The body weights, body fat percentages, and body condition scores were higher 5 to 8% higher in the horses on the higher energy diet.
In the standardized treadmill test, the horses that had put on weight and body fat showed a higher heart rate, as well as increases in plasma lactate concentration, respiration rate and rectal temperature than the horses on the restricted diet.
The overall blood test results of the heavier horses were indicative of lower physiological fitness.
The authors also found that objective locomotion asymmetry was higher in the heavier horse group, based on sensor measurements.
The second exercise assessment involved a field test simulating a breed evaluation field test for Icelandic horses, in which riding abilities and gaits are scored by judges. Two certified judges were used in the study.
Judges’ scores for gallop, form under a rider, and total score for riding abilities were lower for the heavier horses. Scores for tölt and pace showed a tendency to be lower among the heavier horses.
The researchers, discussing their findings, said they believe their study is the first to examine the effect of increased body fat content and body weight on metabolic and physiological exercise response and performance in horses in a controlled cross-over study.
The results clearly show that an increase in body fat percentage, body weight, and body condition of 5 to 8% lowers physiological and metabolic fitness, based on the parameters assessed.
“It also impairs true performance evaluated by judges blinded to the treatments, and appears to induce locomotion asymmetry, measured objectively using a sensor technique.”
They noted that the locomotion asymmetry seen in the heavier horses was most pronounced in the front limbs one day after their performance in the field test.
“This indicates that weight gain may have a negative impact on the locomotion apparatus and that the effect may be amplified after acute exercise.”
The authors said higher body fat content and body weight in horses was shown to alter metabolic and physiological responses to exercise by more than could be expected from increased weight load alone.
“Higher body fat content and body weight in horses also lowered true performance, caused locomotion asymmetry, and delayed recovery from exercise.”
The study team comprised Jansson, Sara Ringmark, Einar Ásgeirsson, Tanja Jóhannsdóttir and Charlotta Liedberg, all with the Swedish University of Agricultural Sciences; and Vikingur Gunnarsson, Sveinn Ragnarsson, Denise Söderroos and Guðrún Stefánsdóttir, all with Hólar University.
Increased body fat content in horses alters metabolic and physiological exercise response, decreases performance, and increases locomotion asymmetry
Anna Jansson, Vikingur Þ Gunnarsson, Sara Ringmark, Sveinn Ragnarsson, Denise Söderroos, Einar Ásgeirsson, Tanja R. Jóhannsdóttir, Charlotta Liedberg, Guðrún J. Stefánsdóttir
Physiological Reports, 10 June 2021, https://doi.org/10.14814/phy2.14824