Graduate Thesis Or Dissertation
 

Viruses associated with respiratory disease : a study of sheep in an Oregon and Colorado feedlot

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dr26z1000

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  • A study was undertaken to determine the prevalence of virus infection in lambs undergoing respiratory tract disease (RTD). The investigation was divided into three study groups and consisted of lambs which were 4 to 5 months of age. In the first group (N=200), paired serum samples were taken from lambs (on entry into the feedlot and 21 days later). In addition, lambs in the group which died of RTD were necropsied and tissue was cultured for the presence of bacteria and examined for viral antigen by fluorescence microscopy, (respiratory syncytial virus, RSV; parainfluenza-3 virus, PI-3; border disease virus, BDV; and ovine adenovirus-6, OVA-6). During the 21 day test period, 47 lambs died of RTD but only 40 were available for study. Antigen to RSV was detected most frequently (37.5% of cases). This was followed by PI-3 (23%), OVA-6 (15%) and BDV (7.5%). More than one virus was detected in 20% of cases. Ten different bacteria were isolated from lung tissue. There were not enough isolations of bacteria to statistically associate a specific type of bacteria with any of the viruses. Paired serum samples from surviving lambs (N=153) were examined for seroconversion to the viruses tested above plus blue tongue virus (BTV). Seroconversion to PI-3 was most commonly observed (47% of cases). This was followed by RSV (35%), OVA-6 (16%), BDV (5%) and BTV (2%). The second Oregon study involved a seroprevalence from a representative number of lambs (N=50) from five different pens in the feedlot at the same time as the first study (each pen contained 200 lambs). Serum samples were taken as lambs entered the feedlot and a second sample (N=50) was taken from lambs from same group 24 days later. A significant increase (P=.OO1 to .05) in the percentage of lambs possessing antibodies to the test viruses was detected in all cases. The most dramatic change occured with RSV (36% to 88% prevalence) and OVA-6 ( 48% to 86% prevalence). Changes in percentage of lambs with antibodies to PI -3 and BDV were less dramatic. The third study was undertaken in a Colorado feedlot. Serum samples were taken as lambs entered the facility (N=200) and a second (paired) serum sample was taken 21 days later from the same lambs. Nineteen lambs died of RTD but they were not examined for presence of viral antigen. Seroconversion in surviving lambs was highest with PI-3 (51%). This was followed by OVA-6 (19%), RSV (17%) and BTV (1%).
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