Agnieszka Sergiel, Institute of Nature Conservation of Polish Academy of Sciences

Haematological parameters are key indicators of blood function and provide valuable insight into animal health and physiological responses to environmental conditions. Commonly used indices include haemoglobin (Hgb) concentration, red blood cell (RBC) count, haematocrit (Hct), and differential leukocyte counts. These parameters vary with external factors (e.g., temperature, altitude, season), internal physiological or pathological states, individual characteristics such as sex and age, and anthropogenic influences, including capture and handling procedures. Population-specific reference intervals are therefore essential for accurate interpretation. Although haematological reference ranges for brown bears have been reported for several North American and European populations, their applicability across populations may be limited because of differences in stress exposure, capture methods, anaesthetic protocols, and blood sampling procedures. We aimed to establish haematological reference intervals for a brown bear population in the Greater Yellowstone Ecosystem of North America, using a long-term dataset of complete blood counts. The reference population was selected a posteriori and comprised 203 clinically healthy individuals (68 females and 135 males) ranging in age from 2 to 30 years. We classified bears into four age categories: subadults (2–4 years, n = 54), young adults (5–9 years, n = 76), prime-aged adults (10–18 years, n = 59), and geriatric individuals (≥19 years, n = 14). Sampling occurred across spring (n = 58), summer (n = 58), and fall (n = 87). We estimated reference intervals using the reflimR package in R following a three-step approach of data exploration, evaluation of extreme or biologically implausible values, and stratification by sex, age class, and season. The resulting intervals provide population-specific baseline values for health assessment and long-term monitoring of brown bears in the Greater Yellowstone Ecosystem.