For many decades vaccines against the J5 core antigen of coliform bacteria have been used in dairy cattle. Early studies comparing vaccinates to unvaccinated controls indicated a reduced incidence of clinical mastitis. In further studies comparing vaccinates to unvaccinated controls, those cows administered a 2-dose J5 vaccine showed less milk loss and less severe clinical coliform mastitis and culling/death. Despite widespread use there have been no randomized controlled field trials using natural infection comparing commercially available 3- dose gram negative core antigen vaccines to commercially available 2-dose vaccines with regards to udder health, reproductive, and productive outcomes.

The objective is to evaluate three commercially available vaccines using labeled dosing, including the Bovilis® J5 (Merck & Co, Rahway, NJ) using 3 doses, Endovac-Dairy® (Endovac Animal Health LLC, Columbia, MO) using 2 doses, and JVACTM (Boehringer Ingelheim Animal Health USA Inc., Athens, GA) using 2 doses on important outcomes associated with clinical mastitis in dairy cows.