Jury still out on whether ponies are “hot blooded” or “cold blooded”

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The researchers set out to investigate whether blood parameters differed among pony classes and to check if general normal values for equine species are applicable to them.
The researchers set out to investigate whether blood parameters differed among pony classes and to check if general normal values for equine species are applicable to them. Photo by Steve Bittinger

Blood lactate levels differ significantly between height classes in healthy ponies, researchers have found.

Olga Witkowska-Piłaszewicz and her fellow researchers have laid out their findings in a study that explored variations in blood and biochemical parameters in healthy ponies.

The study team, writing in the journal BMC Veterinary Research, noted that breed-specific reference ranges for selected blood parameters are recommended for proper interpretation of blood tests. However, there are few reports dealing with ponies.

The researchers set out to investigate whether blood parameters differed among pony classes and to check if general normal values for equine species are applicable to them.

They noted that, in the context of blood chemistry, ponies have been suggested to be more like “hot-blooded” than “cold-blooded” horses. However, other sources categorise ponies as “cold-blooded”.

Their study enrolled 73 Class A ponies up to 121cm in height, comprising eight Shetlands, three Welsh and 62 crossbreed ponies. There were also 28 Felin ponies (125 to 136cm at the withers) and 41 Polish Konicks (130 to 140cm).

The researchers found that all biochemical parameters measured differed significantly between the pony classes except total protein concentrations.

The most pronounced difference was noted in blood lactate concentrations, which were higher in the smallest ponies (Class A).

In the context of blood chemistry, ponies have been suggested to be more like "hot-blooded" than "cold-blooded" horses.
In the context of blood chemistry, ponies have been suggested to be more like “hot-blooded” than “cold-blooded” horses, researchers say. Photo by Myprofe

In all 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. Blood lactate concentrations among the Class A ponies were high in comparison with normal values for horses, they reported.

“Normal values for equine species should not be directly applied to interpret the lactate, triglycerides, aspartate aminotransferase and creatine kinase values in ponies,” they concluded.

Discussing their findings, they said it was still a matter for debate whether ponies should be classified as “hot-blooded” or “cold-blooded” horses from a haematological standpoint.

“One of the important findings in our study is a higher concentration of lactate in class A ponies, but not classes B and C represented by Felin ponies and Polish Koniks, respectively.”

This, they said, was important from a diagnostic standpoint, as lactate levels are commonly used as diagnostic and prognostic indicators in gastrointestinal and ischemic emergencies in horses.

They noted that several studies have mentioned differences in liver functions between horses and ponies. The scientists in the current study also found differences: Aspartate aminotransferase and gamma-glutamyl transpeptidase in all groups of ponies were high, and in Polish Koniks the latter markedly exceeded the reference intervals for hot-blooded horses.

Differences regarding muscle enzymes also seem possible. Creatine kinase (CPK) activity was surprisingly high in class A and Polish Koniks.

“We postulate that high CPK values were related to muscle mass and composition, which were not examined in our study, but such differences in ponies have been reported in the literature.”

Another important finding was the low concentration of triglycerides in all pony groups. They were lower than reference values for hot-blooded horses and were lowest among the Class A ponies. Additionally, levels tended to decrease with age.

It is generally believed that healthy ponies may have higher triglyceride levels, and low concentrations are therefore not of diagnostic relevance. Higher triglyceride values have been reported, but lower values have predominated in more recent studies involving ponies.

“This,” they said, “is particularly important for practitioners because metabolic disturbances leading to hyperinsulinemia and equine metabolic syndrome include a moderate elevation of triglyceride concentrations.

“If ponies normally have low triglyceride concentrations and practitioners use reference values for hot-blooded horses, ponies actually having hypertriglyceridemia may be misdiagnosed, because ponies with mildly elevated triglycerides, interpreted according to the reference values for hot-blooded horses, may in fact have markedly elevated triglycerides.

“Thus, we postulate that the normal triglyceride values for ponies should be reconsidered or at least treated with caution.”

“It is also noteworthy that in all groups of ponies examined by us, the concentrations of urea were higher and creatinine lower than recommended for full-sized horses.”

Another finding in Polish Koniks was a significantly lower glucose concentration than in other groups of ponies and also lower than normal values reported for hot-blood horses.

Polish Konicks up to 140cm were among the ponies studied.
Polish Konicks up to 140cm were among the ponies studied. Photo by Erik van Roekel

“The differences between full-sized horses and ponies in glucose and insulin metabolism, oxidative capacity and response under sympathetic stimulation are widely reported in the literature.

“Even though higher glucose concentrations, reflecting metabolic differences, have been clearly shown in ponies with gastrointestinal diseases, these differences are frequently not noticeable at rest but only during dynamic response testing.”

The authors said the main limitation of their study was the number of ponies in examined groups, which were too small to establish reliable reference intervals for groups.

“In conclusion, our study proved breed-related differences in haematological and blood biochemical parameters in the ponies. In our opinion, normal values for ponies should vary at least with the height classes. Special attention should be paid to the interpretation of blood lactate and triglyceride values, especially in cases where ponies are being evaluated for clinical disease.”

The study team comprised Witkowska-Piłaszewicz, Anna Cywińska, Katarzyna Michlik-Połczyńska, Michał Czopowicz, Katarzyna Strzelec, Anna Biazik, Marta Parzeniecka-Jaworska, Mark Crisman and Lucjan Witkowski, variously affiliated with a range of institutions in Poland, including the Warsaw University of Life Sciences and the Poznan University of Life Sciences. Crisman is with the Virginia Maryland College of Veterinary Medicine, part of Virginia Tech in Blacksburg in the United States.

Witkowska-Piłaszewicz, O., Cywińska, A., Michlik-Połczyńska, K. 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

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

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