First question, do you have enough bulls? Use your conception rate to work out roughly how many bulls are required, take into consideration any influxes from synchro returns (would it be better to keep the technician on hand or should you put more bull power in to mitigate?). Or use this table.
Rotate bulls at least every 48 hours, daily if possible. This will help their drive, ensure they are making enough semen and help reduce risk of lameness or injury from over-working.
Observe regularly to ensure they are serving correctly, any signs of problems remove them and replace with able-body bulls.
If a bull falls lame or ill at any stage he’s out for the rest of the season. Semen production takes two months, if a bull’s body temperature raises due to fever or heat stress at any stage it can cause major disruption to semen production and mating will be over before his production has recovered.
For a quick calculation check out the table on page 136 of the second edition of the InCalf book.
Example: If you have a 400-cow herd and figure that 60% are in-calf to 5 weeks AB, then you need 6 bulls in with these cows at any one time. Another 6 will be required if you are rotating two bulls teams.