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Enzymic activity, metabolites, and hematological responses for reference intervals (RIs) establish ranges of physiological normality, which are useful for diagnosing diseases and physiological alterations. Within the same species, RIs vary according to age, gender, productive and physiological states, and environmental factors including health management and nutrition. RIs have been extensively studied in dairy calves during a critical stage of life (from birth up to first 90 days of age). A critical stage for feedlot calves is their arrival at the feedlot, but no reports determine RIs for different enzymic activity, metabolites, and hematological responses during their initial period at the feedlot. Consequently, a total of 461 high-risk crossbreed beef calves, received on three different dates, were examined upon arrival at the feedlot. Of these, 320 calves (148.3 ± 1.3 kg body weight) whose “clinical health” was evaluated were included in the study. Blood samples were taken upon arrival and on days 14, 28, 42, and 56 to determine the following parameters: enzymic activity, metabolites, electrolytes, white blood cells, platelets, and red blood cells. Enzymic activity, metabolites, and complete blood count were determined by automated analyzers. The freeware Reference Value Advisor Software was used to calculate the non-parametric values of RIs. This study is the first to establish RIs for different enzymic activity, metabolites, and hematological responses in high-risk newly received calves during their initial period at the feedlot. This information will be useful for veterinary clinical practice and research related to the health and welfare of high-risk newly received calves during their initial period at the feedlot.