Masters Theses

Date of Award

12-1980

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

J.B. McLaren

Committee Members

P.C. Smith, R. D. Walker, D.A. Bemis

Abstract

The role of Pasteurella hemolytica in the bovine respiratory disease (BRD) complex was studied in two trials involving feeder steer calves. In Trial I, 54 calves were purchased from two Tennessee producers. The calves were followed through the market-transit chain which terminated at a feedlot at the Highland Rim Experiment Station (HRES) near Springfield, Tennessee. The calves were subjected to one of three infectious bovine rhinotracheitis (IBR) vaccination regimes, (1) injection with an IBR vaccine 30 days prior to delivery to the auction barn (AB), (2) injection with vaccine 30 days prior to delivery to the AB followed by a cell mediated immune booster upon arrival at the AB, and (3) nonvaccinated control group. On the day prior to departure from the orderbuyer barn (OBB) the calves were challenged by nasal inoculation with IBR virus. In Trial II, 48 calves purchased from auction barns were transported to a feedlot at the University of Tennessee Blount Farms at Knoxville, Tennessee.

Body weights of the calves in both trials were taken at various sampling dates. The weights were used to calculate gains as a measure of feedlot performance. Serum harvested from blood samples obtained at various points during the two trials were used to demonstrate the presence of and changes in antibody titers against Pasteurella hemolytica. An Enzyme-Linked Immunosorbant Assay (ELISA) technique was used to measure antibody titers in serum of calves from both trials. The presence of antibodies in the serum of the Blount Farm calves was also determined by an agglutination technique.

A scoring system involving the evaluation of various health parameters was used to monitor clinical signs of disease in the HRES calves. The number of days the calves were judged by the herdsman to require treatment for disease was used as a measure of disease severity in the Blount Farm calves.

Chi-square analysis of the frequencies of positive and negative antibody titers indicated that the ELISA and agglutination techniques gave comparable results when ELISA titers greater than or equal to 128 were considered positive and titers less than 128 were considered negative.

Pasteurella hemolytica was isolated from 2% of the HRES calves and 47% of the Blount Farm calves which were sampled. Pasteurella hemolytica antibody titers in the HRES calves remained low and consistent throughout the market-transit and feedlot phases. In the Blount Farm calves, a large increase in antibody titers occurred in sera taken upon arrival at the feedlot and sera obtained 38 or 43 days later. These results indicate that Pasteurella hemolytica infection occurred in the Blount Farm calves but not in the HRES calves.

Antibody titers of the second serum samples were positively correlated with the number of days sick and negatively correlated with the average daily gains of Blount Farm calves. This suggests that Pasteurella hemolytica infection had an adverse affect on feedlot performance.

Clinical signs of disease evident in the HRES calves suggested that the calves were infected with IBR virus. The nonvaccinated calves were more severely affected by the IBR infection than the vaccinated calves. This was evident in greater degrees of respiratory distress, necrotic rhinitis, higher rectal temperatures and higher daily health indexes. No differences in degrees of mucopurulent nasal discharge and percent packed cell volumes were observed. Calves receiving the IBR vaccination followed by the cell mediated immune booster gained more weight from feedlot day 1 to feedlot day 10 than nonvaccinated calves. Weight gain differences due to IBR vaccination had disappeared by feedlot day 22.

In conclusion, the results indicate that Pasteurella hemolytica is an important etiological agent of the BRD complex in market stressed calves. Due to the apparent lack of Pasteurella hemolytica infection, a relationship between Pasteurella hemolytica and IBR virus in the BRD complex could not be demonstrated in the HRES calves.

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