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Young foals have to go through a lot of transforming periods and their bodies have to adapt to the outer environment constantly. The direct evidences of the adaptation process are the variations of the values of physiological and other laboratory parameters compared to those of the adult individuals.
Myeloperoxidase (MPO) indicating the activity of neutrophils is already routinely used in human medicine and measured by the CBC automatic analyser. This method is also applied in some equine neonatal intensive care units in the world. Other techniques evaluating different sample types and under different physiological or disease status were carried out, mostly in adult horses. Since the majority of the reports showed that MPO is a promising indicator of inflammatory processes, it seemed mandatory to investigate its role in foals. Therefore, we aimed to find answers to the following questions: 1. The relationship between MPO activity levels and the age of the foals. 2. Differences of MPO activity patterns between healthy and sick foals within age groups. 3. Whether MPO activities change during treatments.
Thirteen healthy foals and thirty ill hospitalized foals were included in this study. They were allocated to four subgroups based on their age at the time of sampling. Samples of healthy foals were taken at the age of 1-3, 4-19, 20-59 and 60-130 days. From ill hospitalized foals samples were collected at 0, 12, 24 and 48 hours after admission if possible. Based on the kinetic test, plasma samples were applied for the MPO photometric activity assay in the present study.
There were statistical differences of plasma MPO activities between different age groups in healthy foals. We therefore inferred that age plays an important role in plasma MPO activity. The comparisons of plasma MPO activity between healthy and sick foals within age groups did not differ in all four groups. However, sick foals had a much wider range of plasma MPO activities; values as much as four times of the highest measurement in healthy foals were seen in some sick individuals. Unfortunately we could not carry out the statistical comparison between plasma MPO activities and the severity of inflammatory status because of our limited but also multifarious study population. However, foals with elevated plasma MPO activities often also had leukocytosis/leukopenia and/or neutrophilia/neutropenia. The majority of the ill hospitalized foals were discharged; yet, each one of them had a different duration of recovery and hospitalization. In the present study we only evaluated the plasma MPO activities until 48 hours after admission, which is why we have no data on complete duration of recovery.
In this study we demonstrated a suitable method of evaluating plasma MPO activities in foals and we were able to demonstrate that plasma MPO activities were affected by age. Sick foals tended to have a wider range of plasma MPO activities; most of the foals with increased plasma MPO activities also had abnormal leukocyte and/or neutrophil counts, which indicated an inflammatory response. Moreover, foals with an increased or decreased neutrophil concentration but normal plasma MPO activity demonstrated a possible correlation between plasma MPO activity depending on the type and/or severity of inflammation. Further investigations with clearly defined inclusion criteria are necessary to answer the questions about the relationships between plasma MPO activity and the severity of the inflammatory status and the response to the treatments.