To the authors’ knowledge, current data regarding RI for haematological and blood biochemical parameters in ponies are limited. Additionally, it is still a matter for debate whether ponies should be classified as “hot-blooded”  or “cold-blooded” horses  from a haematological standpoint. Practitioners more often use RI for the former group.
It is commonly accepted that erythrogram values (RBC, HGB, HCT) are lower in cold-bloods than in hot-bloods. It has been stated that ponies’ haematocrit may be as low as 0.24 l/l, moreover, in American Miniature horses MCV, MCH and MCHC were higher . WBC counts have been reported as slightly lower in cold-blooded than hot-blooded horses and neutrophil to lymphocyte ratios (N:L) were 1.0 in Arabians and Thoroughbreds, 1.7 in cold-blood horses and 0.67 in American Miniature horses .
Erythrogram values determined in the ponies enrolled in our study did not differ among groups and were much lower than accepted for adult Thoroughbreds and moderately lower than recommended for hot-blooded  and Hucul horses . Hucul horses are small (132-145cm high), so meet the general height criteria for ponies, but from genetic point are closer to hot-blooded horses. The differences between haematological parameters in Huculs and Felin ponies were quite surprising, due to ancestry, suggesting more similarities . It was also surprising that no pronounced differences were observed in HCT values between the ponies examined in our study and hot-blood horses. Similar haematological data have been reported for Noma and Kiso horses [4, 28], Shetland ponies , ponies in regular show jumping and eventing training  and Polish Koniks examined previously . Interestingly, Bosnian ponies similar in size to Felin ponies and Polish Koniks had higher erythrogram values .
Leukogram values determined in our study were similar to values for hot-blooded horses but the N:L was below 1.0, confirming the previous findings in ponies . However, Shawaf et al.  have shown that in Shetland ponies WBC was higher in summer than in winter, butregardless of season the values were higher than in our study. Also, the N:L ratio was above 1.0 in summer and winter . In Noma horses WBC count was similar to the values determined in our study, but N:L ratio was above 1.0 . It has been shown that granulocyte activity and the onset of inflammation differs between horses and Shetland ponies, being more robust in the latter . Wilmink et al.  did not define the numbers of granulocytes, N:L ratios and WBCs, so we cannot compare our data with their findings. It might be postulated that the N:L ratio is one of breed related difference among ponies. However, it cannot be excluded that these differences were related to geographical region, as the cited studies were performed in Japan  and Saudi Arabia , not central Europe.
Erythrogram and leukogram values determined in our study were also related to the age of ponies, in the manner described recently in Spanish Purebreds . Similarly as reported by Satue et al. , we observed that RBC decreased with age with compensatory increase of MCV and MCH. WBC also decreased with age, and although N:L ratio was not significantly increased in our study, neutrophil counts were higher and lymphocyte counts were lower, suggesting similar tendency. Vast similarities between the patterns of changes identified in our results and reported by Saute et al.  confirm their conclusion that age related changes pose the natural condition reflecting a decrease of the bone marrow response.
Haematological features, determined in our study pose an interesting breed and age related finding but of limited diagnostic importance. However, observed biochemical differences are diagnostically important.
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 observation is important from the diagnostic standpoint, as blood and peritoneal LAC are commonly used as diagnostic and prognostic indicators in gastrointestinal and ischemic emergencies in horses. It has been reported that LAC measurement at admission and the changes over time discriminate between survivors and non-survivors and indicate the need for surgical intervention [11-13, 15-17, 35]. All the previously referenced studies involved large, but mixed breed populations with various conditions, so the values indicating guarded prognosis varied among reports. Mean blood lactate concentrations at admission for non-survivors were reported as 4.1 mmol/L with repeated measurements recommended . Another studies suggested values below 2.1  or above 9.548 mmol/L  for non-survivors and a cut-off value of <6.0 mmol/L for survivors . Delesalle et al, 2007  stated an LAC value of 6.3 mmol/L for non-survivors, and recently an optimal decision tree has been proposed which identifies horses as non-survivors when the LAC at admission is ≥ 4.3mmol/L . Only in the last study ponies (27.3%) and Icelandic horses (31.8%) constituted the majority of the observed population, but breed differences in LAC measurements were not investigated. Ponies received more attention in Dunkel’s et al. study  where the mean LAC values for non-survivors were 4.1 and 3.1 mmol/L for ponies and horses, respectively, and did not differ significantly. However, the value for survivors was significantly higher in ponies (2.5 mmol/L) than in horses (1.2 mmol/L) and the authors concluded that ponies could be falsely suspected of having a surgical lesion or a poorer prognosis as they might present higher blood lactate concentrations. LAC concentrations in healthy ponies have been rarely determined. Recently, Dunkel et al.  published a study involving a large group of healthy ponies and determined that the mean LAC concentration was 0.7 (0.2‐2.7) mmol/L and was lower than in full-sized horses: 0.9 (0.2‐1.9) mmol/L. The authors concluded that lactate concentrations depended both on body condition and age . Although the investigated population was large (101 animals), ponies were defined only on the basis of height (≤148 cm), and no data regarding breed or height classes were given. Our findings seem to substantially complement their study and provide additional clinically important information. In our study L-lactate concentrations, when compared to commonly accepted values for hot-blooded full-size horses <0.7 mmol/L [9, 10] or 0.9 mmol/L  were high only in class A ponies’ (median of 1.1 mmol/L) but much lower in Felin ponies and Polish Koniks (median of 0.1 mmol/L in both) representing class B and C, respectively. The causes of different LAC concentration in ponies are unknown. However, LAC may be associated with either increased production or decreased clearance .
Several studies mentioned differences in hepatic functions between horses and ponies [17, 36]. Our study indicates that AST and GGTP in all groups of ponies are high and in Polish Koniks GGTP markedly exceeds the reference intervals for hot-blooded horses. In clinical conditions, elevation of AST and GGTP indicates hepatocellular injury . The ponies in our study were clinically healthy and liver parameters were not high enough to indicate or even suggest hepatic disease, but physiological differences regarding the function of hepatocytes may be suspected. This hypothesis seems in line with the differences described in Noma and Kiso ponies . In both Japanese breeds GGTP concentrations were lower than in the ponies examined in our study, but AST in Noma ponies was higher than in Kiso ponies  and very similar to the values measured in our study. However, in Shetland ponies in Saudi Arabia, GGTP and AST activities were comparably high to the values determined in our study only in the winter .
Difference regarding muscle enzymes also seem possible. CPK activity was surprisingly high in class A and Polish Koniks. Such high values have not been reported in Shetland ponies, Noma and Kiso ponies [28, 29]. In horses, high values of CPK and AST are indicators of muscle damage, and slight elevation are nonspecific . CPK activities up to 10 000 U/l are considered small, nonspecific elevations , which may be associated with transport or exercise . However, in performance horses much lower muscle enzyme activity occur after exercise [39, 40]. Ponies in our study were not transported and did not exercise. CPK activity never exceeded 1300 U/L, and AST activity was not high enough to suggest any muscle pathology. Thus, 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 . This hypothesis seems in line also with observed in our study sex related differences in CPK activity, being higher in females.
Another important finding in our study was the low concentration of TG in all groups of ponies. Values were lower than referenced for hot-blooded horses and the lowest in the smallest class (class A ponies: 0.30±0.15 mmol/l) and additionally, decreased with age. Metabolic differences between horses and ponies in glucose and triglyceride metabolism and tendencies to develop hyperlipemia in a negative energy balance are widely reported in ponies [17, 19, 20, 23, 42]. It is generally believed that healthy ponies may have higher TG levels  and thus, low TG concentrations are not of diagnostic relevance. Higher TG values 78.5±11 mg/dl (0.89±0.12 mmol/l) have been reported  but in more recent studies with ponies lower values predominate. Ono et al.  reported 37.2±34.3 mg/dl (0.42±0.39 mmol/L) for Noma horses and Takasu et al.  16.4±11.1 mg/L (0.19±0.13 mmol/L) for Kiso horses. Even in pony mares in late gestation TG values as low as 11.3±5.4 md/dl (0.13±0.07 mmol/l) have been measured .
This is particularly important for practitioners because metabolic disturbances leading to hyperinsulinemia and equine metabolic syndrome (EMS) include a moderate elevation of TG concentrations [22, 23]. If ponies normally have low TG concentrations and practitioners use reference values for hot-blooded horses (reference interval from 0.2 to 1.2 mmol/L) , ponies actually having hypertriglyceridemia may be misdiagnosed, because ponies with mildly elevated TG, interpreted according to the reference values for hot-blooded horses, may in fact have markedly elevated TG. Thus, we postulate that the normal TG value 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. Similar finding has been reported in American Miniature horses . In Shetland, Noma and Kiso ponies creatinine concentrations were also low, but blood urea nitrogen (BUN) was lower than measured in our study [28, 29]. However, urea and creatinine concentrations appeared to be affected by sex rather than by breed. .
Another finding in Polish Koniks is a significantly lower glucose concentration than in other groups of ponies and also lower than normal values reported for hot-blood horses . This has also been reported in Shetland ponies, regardless of season, , Noma and Kiso ponies  and mixed population of ponies . However, it is similar to the value reported previously in Polish Koniks . 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 [21-23, 36, 46]. 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 [18, 21].
The main limitation of our study was the number of ponies in examined groups, too small to establish reliable reference intervals for groups. It should also be mentioned that differences in haematological and biochemical values may be associated with the method of the test or even equipment. The methods used in our study are routine in other laboratories, except hand-held lactate and glucose analysers, that are used in field practice. Accusport analyser used in this study has been evaluated in horses and successfully used in other studies. It has been shown that Accusport is reliable and accurately measured plasma lactate concentration in horses so that they are comparable to values from other analysers [47, 48]. The differences in age and sex distribution between groups were controlled in the statistical analysis so it is unlikely that they negatively affected the results obtained.