Effects of 3-methylindole production and immunity against bovine respiratory syncytial virus on development of respiratory tract disease and rate of gain of feedlot cattle.
OBJECTIVE
To determine whether immunity against bovine respiratory syncytial virus (BRSV) mitigates the effects of 3-methylindole (3MI) on occurrence of bovine respiratory tract disease (BRD) and rate of gain in feedlot cattle.


METHODS
254 mixed-breed beef cattle.


METHODS
Cattle were randomly assigned to 1 of 3 groups at the time of arrival at the feedlot. One group was vaccinated with an inactivated BRSV vaccine, another was vaccinated with a modified-live BRSV vaccine, and the third was maintained as unvaccinated control cattle. On days 0 and 28, serum BRSV antibody concentrations were measured, using serum neutralizing and ELISA techniques. Serum 3MI concentrations were measured at feedlot arrival and 3 days later. Cattle were monitored for development of BRD. At slaughter, lungs were evaluated grossly for chronic lesions.


RESULTS
Higher serum 3MI concentrations early in the feeding period were associated with lower mean daily gain. Control cattle were more likely to be treated for BRD after day 3, compared with cattle vaccinated with the modified-live BRSV vaccine. Humoral immunity against BRSV did not appear to modify the effect of 3MI on development of BRD or mean daily gain.


CONCLUSIONS
Results suggest that abrogating the effects of 3MI and BRSV infection may improve the health and growth performance of feedlot cattle. However, in this study, immunity against BRSV did not appear to protect against the potential synergism between 3MI and BRSV infection, possibly because of the slow rates of gain of cattle included in the study or timing of sample collection.
Bingham
H R
HR
Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus 43210, USA.
Morley
P S
PS
Wittum
T E
TE
Bray
T M
TM
Ellis
J A
JA
Queen
W G
WG
Shulaw
W P
WP
D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D000914:Antibodies, Viral / Q000032:analysis; D002417:Cattle; D002418:Cattle Diseases / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D008297:Male; D018357:Respiratory Syncytial Virus Infections / Q000276:immunology / Q000662:veterinary*; D018112:Respiratory Syncytial Virus, Bovine / Q000276:immunology*; D012862:Skatole / Q000378:metabolism*; D015430:Weight Gain / Q000187:drug effects*
D000914:Antibodies, Viral; D012862:Skatole