Passive immunity occurs when 'preformed' antibodies are made in one animal and passed onto another. For example a cow passes on her own antibodies to her calf via colostrum (first milk after parturition) and milk. | Passive immunity occurs when 'preformed' antibodies are made in one animal and passed onto another. For example a cow passes on her own antibodies to her calf via colostrum (first milk after parturition) and milk. |