Blood tests are crucial in diagnosing a range of problems in horses, but researchers caution that there are significant variations in some blood and biochemical parameters between healthy horses and ponies.
Not only that, but the study team in Poland also found important variations between healthy ponies, depending on the height class to which they belonged.
Normal values for equine species should not be directly applied to interpret the lactate, triglycerides, aspartate aminotransferase and creatine kinase values in ponies, Olga Witkowska-Piłaszewicz and her fellow researchers wrote in the journal BMC Veterinary Research.
The study team set out to investigate if blood parameters differed among pony classes and to check if general normal values for equine species applied to ponies.
They used ponies of different origins and height, represented by small ponies (class A – up to 121 cm), Felin ponies and Polish Koniks.
The Polish Konik is a primitive breed, descended directly from the wild tarpans. They are small in stature (132-136 cm, so belong to height class C), have modest living requirements and high resistance to disease and environmental conditions.
Felin ponies represent a relatively new breed for riding and competitive events for young riders. They originate from Arabians, Polish Koniks, Welsh ponies and Malopolski horses. While from a genetic standpoint, Felin ponies may be treated as “hot-blooded” horses, according to their height (125-136 cm) they belong to class B or C.
The study involved 142 riding ponies in all. The 73 class A ponies in the study included eight Shetland ponies, three Welsh ponies and 62 crossbred ponies, aged 2 to 31.
There were 28 Felin ponies, aged 2 to 29. Polish Konik horses numbered 41 and were aged 2 to 16.
All blood samples were obtained during routine health checks, performed in August, under similar weather conditions.
With the exception of total protein concentration, all biochemical parameters measured significantly differed among ponies’ classes, the researchers reported.
The most pronounced difference was noted in blood lactate concentrations, which were higher in the smallest ponies (class A). Only ponies in this class showed levels higher than conventional values for full-size horses. The bigger ponies returned values within the normal range for horses.
In all three groups of ponies, muscle enzymes (aspartate aminotransferase and creatine kinase) and urea were high when compared to normal values for equine species, but triglycerides and creatinine were low.
The authors noted that, in the context of haematology and blood biochemistry, ponies have been suggested to be more like “hot-blooded” than “cold-blooded” horses. However, other sources include ponies in the “cold-blooded” category.
“Consequently, clinicians must interpret the common reference intervals with caution, as they may not be directly applicable to the pony practice.
“Several differences are likely important in assessing general health, fitness, stress, welfare and performance or even critical for proper diagnosis in sick animals.”
One of the most commonly discussed differences between horses and ponies are glucose and triglyceride metabolism and cellular response to catecholamines, which may promote metabolic diseases.
“Ponies are less sensitive to insulin, so the rapid development of hypertriglyceridemia resulting from insulin resistance seems more likely.”
In the global literature, there have been only a few reports dealing with blood parameters for ponies, the study team noted.
Discussing their results, the researchers said the higher concentration of lactate in class A ponies, but not classes B and C ponies used in the study, is an important finding.
“This observation is important from the diagnostic standpoint, as blood and peritoneal levels of L-lactate are commonly used as diagnostic and prognostic indicators in gastrointestinal and ischemic emergencies in horses.”
Differences regarding muscle enzymes also seem possible, they said. Creatine kinase activity was surprisingly high in class A and Polish Koniks. “Such high values have not been reported in Shetland ponies, Noma and Kiso ponies,” the authors noted.
The study team comprised Witkowska-Piłaszewicz, Anna Cywińska, Michał Czopowicz, Marta Parzeniecka-Jaworska and Lucjan Witkowski, all with the Warsaw University of Life Sciences; Katarzyna Michlik-Połczyńska, with the Poznan University of Life Sciences; Katarzyna Strzelec, with the University of Life Sciences; Anna Biazik, with Nicolaus Copernicus University; and Mark Crisman, with the Virginia Maryland College of Veterinary Medicine in the US.
Olga, WP., Anna, C., Katarzyna, MP. et al. Variations in haematological and biochemical parameters in healthy ponies. BMC Vet Res 17, 38 (2021). https://doi.org/10.1186/s12917-020-02741-5