Comparison of protection of experimentally challenged cattle vaccinated once or twice with a Pasteurella haemolytica bacterial extract vaccine.
Three groups of calves (15-18 per group) were injected twice at a 3-week interval with 2 doses of phosphate buffered saline (PBS, CONTROL group), 2 doses of PRESPONSE, a Pasteurella haemolytica A1 bacterial extract vaccine (PRESPONSE-2 group) or 1 dose of PBS followed by a 2nd vaccination with 1 dose of PRESPONSE (PRESPONSE-1 group). Three weeks after the 2nd vaccination, the calves were challenged intratracheally with P. haemolytica A1. Calves were evaluated clinically for 3 days prior to challenge and for 5 days after challenge. Six days postchallenge, calves were either euthanized or sent to slaughter and the lungs were evaluated for percent pneumonic tissue. There was a significant effect of single or double application of vaccine on clinical scores (P = 0.0409). Percent pneumonic tissue at necropsy was significantly affected by vaccine group (P = 0.014). Calves in the CONTROL group had significantly higher percent pneumonic tissue after arcsine transformation (45.30%) than calves in any group receiving PRESPONSE, regardless of vaccination frequency (25.18% and 25.78%, for calves receiving 2 doses or 1 dose of PRESPONSE, respectively). Both serum toxin neutralizing and direct agglutinating titers were negatively correlated with percent pneumonic tissue. Most importantly, 1 dose of PRESPONSE was as efficient as 2 doses at eliciting a protective immune response. It is concluded that the presence of P. haemolytica as a natural commensal in the upper respiratory tract of the calf can effectively prime the animal, and allow the animal to respond in an anamnestic nature to only 1 dose of this vaccine.
Conlon
J A
JA
Langford/Cyanamid, Guelph, Ontario.
Gallo
G F
GF
Shewen
P E
PE
Adlam
C
C
D000704:Analysis of Variance; D000818:Animals; D001428:Bacterial Vaccines / Q000008:administration & dosage*; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology / Q000517:prevention & control*; D008297:Male; D010326:Pasteurella Infections / Q000517:prevention & control / Q000662:veterinary*; D013997:Time Factors
D001428:Bacterial Vaccines