Calves vaccinated before 6 months of age should be revaccinated at 6 months of age or at weaning; ideally calves should receive the first dose 2-4 weeks before weaning with booster at weaning. Annual booster is recommended. Safe for pregnant cows.
There are questions as to wether its effective. When they are that young the components of the colostrum interfere with the usefulness of the vaccine. I did hear of a nasal application for young calves that is supposed to be effective but have never used it.
used to have the same problem. lot of calves would get pneumonia unless i vacinated them at 1 month of age with virashield 6. now i vacinate cows each year with virashied 6 2-3 months before freshing & that seem to have eliminated the problem