Researchers have identified metabolic pathways and genes affected by exercise in the blood of Arabian horses, in what could prove to be an important step toward pinpointing signs of overtraining on a molecular level.
The findings of the Polish study could also ultimately help in optimizing training programs for the breed, which is widely employed in endurance and flat racing in some parts of the world.
Arabian horses are one of the oldest and most influential horse breeds in the world, with a reputation for stamina.
Katarzyna Ropka-Molik and her colleagues, writing in the journal BMC Genetics, noted that the racing performance traits of Thoroughbreds had been widely described, but not for Arabians.
Several key differences between the two breeds have already been noted, including a lower maximal rate of oxygen consumption in Arabians and differences in the proportion of certain types of muscle fibres. Such differences added weight to the proposition that Thoroughbred and Arabian horses were conditioned in different ways for performance traits.
The study team said it was well established that intensive, regular training resulted in long-term adaptations – new base levels of gene expression – involved in establishing a new homeostasis, or metabolic balance. However, the exact mechanism that occurs in the blood and muscles of Arabian horses during exercise in relation to stamina and performance was still not well understood.
Some of the most important changes centered around optimizing the transport of oxygen around the body to ultimately improve performance.
On the other hand, an imbalance between exercise and recovery can result in under-performance and progressive fatigue, called overtraining syndrome.
“It seems to be important to distinguish the signs of overtraining from the effects of balanced exercise on the molecular level in order to design molecular tools for training optimization,” they said.
To date, only the protein levels of alpha-1 antitrypsin has been considered as a marker of overtraining in horses based on protein analysis during normal and intensive training.
The researchers set out to identify the genetic basis of changes occurring in the blood of Arabian horses within a flat-race training program.
They examined the global gene expression within blood samples. Gene expression is the process in which genes instruct the body to produce a particular product, usually a protein, which has a special use in the body, such as an enzyme or a hormone.
The researchers explored differences in gene expression between different phases of training, with samples taken from 12 three-year-old Arabian horses in flat-race training after a slow conditioning canter, following intense galloping work, and at the end of the racing season.
They compared the results to those from six untrained two-and-a-half-year-old Arabian horses.
Their molecular analysis of the blood samples identified a series of what are known as differentially expressed genes. These are genes that respond to signals or triggers – in this case training.
The number of differentially expressed genes climbed as the training workload increased, with the greatest differences found between trained horses at the end of the season and those that had received no race training.
Compared with the untrained horses, 40 differentially expressed genes were detected at the slow canter phase, 296 at the gallop phase, and 440 at the end of the racing season.
The most abundant genes up-regulated by exercise were involved in pathways regulating cell cycle, cell communication, proliferation, differentiation and apoptosis (normal cell loss), as well as immunity processes.
The results, they said, highlighted the significance of molecular mechanisms for regulating glucose uptake and lipid metabolism. “These mechanisms are essential for maintaining body homeostasis during long-term exercise in Arabian horses.”
The increased abundance of acute-phase response molecules at higher training levels confirmed that an organism recognized long-term training as a stress factor. These inflammatory responses played an important role in triggering downstream pathways critical to maintaining metabolic balance.
“Thus, understanding the molecular basis of exercise-induced stress can be helpful for identifying performance markers in horses,” they wrote.
The genes identified in the research were essential for maintaining metabolic balance during long-term exercise in Arabian horses. Some of them should be further investigated as markers potentially associated with racing performance in Arabian horses, they said.
The study team listed eight genes in particular − LPGAT1, AGPAT5, PIK3CG, GPD2, FOXN2, FOXO3, ACVR1B and ACVR2A − as the starting point for further research in this area.
“Such markers may be essential for choosing a training regimen, and they can reveal what causes the differences in racing performance that are specific to Thoroughbreds or Arabian breeds.”
The next stage of research, currently under way, involves similar gene-expression analysis in Arabian horse muscle in order to confirm results to date and to detect exercise-induced changes in that tissue.
Ropka-Molik was joined in the study by Kacper Żukowski, Katarzyna Piórkowska, Artur Gurgul and Monika Bugno-Poniewierska, all from Poland’s National Research Institute of Animal Production; and Monika Stefaniuk-Szmukier, from the Institute of Animal Science at the University of Agriculture in Cracow.
Transcriptome profiling of Arabian horse blood during training regimens
Katarzyna Ropka-Molik, Monika Stefaniuk-Szmukier, Kacper Żukowski, Katarzyna Piórkowska, Artur Gurgul and Monika Bugno-Poniewierska.
BMC Genetics 2017 18:31 DOI: 10.1186/s12863-017-0499-1