Scientists unravel the mysteries of endurance horse metabolism

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American endurance officials have laid out a series of concerns in a letter to the US Equestrian Federation. Photo: File

Horses studied in a 160km endurance race made an effective metabolic switch from carbohydrate consumption to lipid consumption, but in doing so managed to maintain higher blood glucose levels than horses competing over shorter distances.

Lipid metabolism is known to take place during endurance exercise as a way of maintaining the energy supply as the glucose level falls. But, interestingly, researchers found that blood glucose levels did not fall as much in horses competing over the longer distances.

Scientists, in a paper published in the journal Frontiers in Molecular Biosciences, have taken what they describe as the first step toward unraveling the energy metabolism in endurance horses.

Laurence Le Moyec and his colleagues noted that the positive or negative effects of exercise on metabolic pathways have been widely studied in humans and animals.

Endurance racing, by its nature, places high physiological demands on energy metabolism pathways.

The study team investigated energy metabolism in 40 horses competing in three race categories, over 90km, 120km, or 160km. Sixteen of the horses competed over 90km, 15 over 120km and 9 over 160km.

The three races took place at Fontainebleau, France, in the same conditions, on the same day.

The similar environmental conditions allowed the researchers to focus on examining changes in energy metabolism in relation to the different distances over which the horses competed.

For each horse, a plasma sample was collected the day before the race, and another was collected at the end of the race.

The samples were analysed to determine the plasma metabolic profile shift in each horse and relate those changes to the distances covered.

They found what they described as an adaptive metabolic switch toward lipid metabolism progressing in the horses from the shortest race distance to the longest race distance.

“Signs of protein breakdown were more apparent in the longest race category,” they reported.

They said the metabolic shift seen in the different racing categories could be related to a mixture of three important factors: the ride distance, the training status, and the inherited endurance capacity of the various horses competing.

Their modeling showed that blood glucose levels were lower in post-race plasma samples than in pre-race samples.

“Glucose seems to contribute to a lesser extent for the 160km race,” they said. Several explanations were possible to explain a lesser glucose level decrease in the 160km horses.

“These horses may better compensate for glucose losses through better use of muscle and liver glycogenolysis or a lack of necessary gluconeogenesis.

“They are probably better trained in this long race category and thus, could increase their muscular and liver glycogen reserves.

“However, other metabolic changes observed in parallel lead us to believe that horses of 160km preferentially use the metabolism of fatty acids for muscular functioning and thus save their glucose and avoid fatigue.”

In all horses, the plasma lactate level was significantly increased after the race.

“One can, therefore, hypothesize that glucose was anaerobically metabolized at least during the last minutes of exercise when the riders asked their horses to increase their speed to the finish line.”

The authors said it might be possible to promote the use of lipid metabolism through appropriate training, dietary measures, and race tactics.

“More research is needed to understand metabolic shifts that take place in horses throughout different types of exercise.”

The full study team comprised Laurence Le Moyec, Céline Robert, Mohamed Triba, Nadia Bouchemal, Núria Mach, Julie Rivière, Emmanuelle Zalachas-Rebours and Eric Barrey, variously affiliated with the University of Paris-Saclay, the French science agency INRA, the National Veterinary School of Alfort, and the national research center CNRS.

A First Step Toward Unraveling the Energy Metabolism in Endurance Horses: Comparison of Plasma Nuclear Magnetic Resonance Metabolomic Profiles Before and After Different Endurance Race Distances
Laurence Le Moyec, Céline Robert, Mohamed N. Triba, Nadia Bouchemal, Núria Mach, Julie Rivière, Emmanuelle Zalachas-Rebours and Eric Barrey.
Front. Mol. Biosci., 12 June 2019 | https://doi.org/10.3389/fmolb.2019.00045

The study, published under a Creative Commons License, can be read here.

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