The severity of bovine respiratory infections has been linked to a variety of factors, including environmental, nutritional changes, transportation, and social reorganization of weaned calves. Fatal respiratory infections, however, usually occur when a primary viral infection compromises host defences and enhances the severity of a secondary bacterial infection. A primary bovine corona viruse(BoCV) respiratory infection followed by a secondary  pasturela multocidaresults in fatal bovine respiratory disease (BRD) and host responses to these two pathogens have been studied extensively. We used this disease model to demonstrate that stress significantly altered the viral–bacterial synergy resulting in fatal BRD. A total of 132 nasal swabs as well as blood samples were collected from diseased calves suffered from acute respiratory tract disease and 28 normal control cavles also were sampled at the beginning of the epizootics as well as 4 weeks after treatement with suitable highly sensitive antibiotic and supportive drugs Ages ranges from 4 -10 months old from 8 herds in winter season. All were examined to establish the extent of involvement of Bovine Corona Virus andPasteurella multocida microorganism. On virological studies, respiratory bovine corona viruses were isolated from nasal secretions of 29 diseased calves classified into 11(8.33%) calves suffered from viral infection only and 18 (13.60%) cases of mixed infection with Pasteurella multocida. But it was not isolated from apparently healthy calves group. On bacteriological investigation 43 clinically diseased calves nasally shed Pasteurella multocida devided to 18(13.60%) cases of mixed infection with BoCV and 25(18.90%) cases of bacterial infection only. Also P.multocida was detected in nasal swabs of 3(10.70%) apparently healthy calves. Isolated bacteria were highly sensitive to cefiquinome, ciprofloxacin, and erythromycin. While it was resistant to Cephradine, nalidixic acid, gentamicin, oxyteteracycline, and cephalexin. Considering the mixed infection, results showed that, simultaneous isolation of the Pasteurella multocida pathogen only from nasopharyngeal swabs of the examined pneumonic calves was relatively high (32.60%), followed by isolation ofCorona virus (22.00%) and the the lowest percentage was mixed infection of both pathogens (13.60%). Mortality rate were markidly decreased after treatment of three groups of calves with cefiquinome antibiotic (Cobactam 2.5 % - 1 Cm / 25 Kg body weight  once daily for 3 successive days) and declophenac sodium as analgesic - antibyretic drug (Declo 5 – 1 Cm / 50 Kg body weight twice daily for 5 successive days) from 10/54(18.50%) to 2/44(4.50%).