Respiratory diseases among horses cause economic losses in foals and productivity decreasesin horses being raised and in adult horses. In South Korea, fundamental studies of horses’ respiratorydiseases and those related to disease occurrence are insufficient. Therefore, the aim if the currentstudy was to use diverse hematological indicators, obtained through hematological tests andmeasurment of blood antibody level in horses suffering form respiratory diseases, to monitor diseaseoccurrence and prognosis evaluation.Viral respiratory infections are common in horses, notably equine herpesvirusinfection and equine influenza, which primarily initiate secondary bacterial respiratoryinfections such as strangles caused by Streptococcus equi equi. A decline in the production ofstallions has been associated with these respiratory diseases leading to adverse financialimplications.Ⅰ.Investigations of infection states by horses’ bacterial respiratory diseases, susceptible drugs, andresisted drugs according to pathogens showed differences between farms. Among the β-lactam-basedantibiotics, cephalosporin-based antibiotics showed some efficacy against Streptococcus spp. Toreview age-based changes in erythrocytometer hemograms in hematological tests of riding horses, redblood cell (RBC) tended to gradually decrease with increasing age this tendency was statisticallysignificant. In addition, leukocytometer hemograms analyzed by age showed that total white bloodcell counts tended to decrease with increasing age..Ⅱ.A low level of equine herpesvirus type 1 (EHV-1) (11.36%) antibodies was detected fromstallions, however a high level of EHV-4 (95.84%) antibodies was detected from horses without vaccination against this infection suggesting that EHV-4 is ubiquitous in this horsepopulation. In case of equine influenza, ranch stallions showed low positive rate (12.06%)whereas stallions from Subtropical Livestock Research Institute displayed higher positive rate(81.32%). Antibody responses against equine influenza and strangles revealed positive ratesof 26.32% and 55.12%, respectively.Ⅲ. Immortalized primary equine epithelial cell lines for mass-producible EHV have been establishedby primary culturing of the equine fetal kidney. In order to set up the conditions, we separated twodifferent cell lines, JNUEK-1 and JNUEK-2, from immortalized primary equine epithelial cells bysingle-cell cloning. The virus titer of EHV-1 TCID50/ml was calculated by inoculation of seriallydiluted virus into a 96-well plate of Madin–Darby bovine kidney (MDBK) cells. The optimalmultiplicity of infection (MOI) was approximately 0.1 for both JNUEK-1 and JNUEK-2 to obtain thehighest titers: 2×109 TCID50/ml and 4×108 TCID50/ml, respectively. The maximum titers of EHV-4came from JNUEK-1, at 7×109 TCID50/ml. As a result, JNUEK-1 was more successful at EHV-1 andEHV-4 production than MDBK.