F01 - Role of Nasal BRSV-IgG1 Titers on Clinical Protection of Calves Against Experimental Challenge with BRSV

Abstract: Background – The role of nasal BRSV IgG1 titers transferred from colostrum on clinical protection against BRSV infection in calves is unknown.
Hypothesis/Objectives – To determine if greater titers of nasal BRSV IgG1 transferred from colostrum protected calves against BRSV challenge.
Animals – Forty, 3-month-old beef steers.
Methods – Randomized, controlled, clinical trial. Forty calves were assigned to 1 of 2 treatment groups. Group Vacc (n=20) nursed colostrum from cows vaccinated with 2 doses of an inactivated-BRSV vaccine before calving. Group NoVacc (n=20) nursed colostrum from unvaccinated cows. At 3 months of age, calves were challenged with BRSV by nebulization. Following challenge, respiratory signs were scored. Nasal secretion and serum samples were collected before and after challenge for nasal IgG1 and neutralizing antibody testing. Nasal secretion samples were collected after challenge for identification of BRSV by RT-PCR.
Results - Following challenge, mild respiratory scores were recorded in both groups (P > 0.05). The proportion of calves with fever was greater in NoVacc calves. Nasal BRSV IgG1 titers were greater in Vacc calves at 48 hours of life (P < 0.05); however, decayed to undetectable levels in both groups before challenge (P > 0.05). Serum BRSV antibodies were greater in Vacc calves at 48 hours and on challenge day. A greater proportion of NoVacc calves tested positive by BRSV RT-PCR after challenge (P < 0.05).
Conclusions and Clinical Importance – Nasal BRSV IgG-1 from colostrum does not play a role in clinical protection of 3-month-old calves experimentally challenged with BRSV.