Abortions occurred in a previously unvaccinated group of 55 commercial beef cows aged, 4-7 years, 4-8 weeks post vaccination. The 55 cows were commingled with the home herd of 170 vaccinated cows on the day of annual revaccination. No abortions occurred in the home herd of 170 cows. The home herd's 130 original mature cows had been vaccinated with an MLV during the open period 10 years previously. Since that time, all replacement heifers are vaccinated at 60-90 DOA and at 12 months of age and one group of 15 purchased replacement heifers were vaccinated with an MLV prior to first breeding 4 years previously. All cows of the home herd, including first-calf heifers, receive an annual vaccination with a 4/5-way MLV and an 8-way clostridial and a "pour-on" parasiticide at 2-3 months pre-calving.
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