Most passive immunity occurs in first six hours
Western Livestock Journal
Despite our best efforts, a few calves will be born via a long, hard delivery. They may be sluggish or weak at birth and slow to find the cow and nurse. These calves are more prone to scours or pneumonia as babies and “poor-doers” later in life.
Resistance to disease is greatly dependent on antibodies or immunoglobulins and can be either active or passive in origin. In active immunity, the body produces antibodies in response to infection or vaccination. Passive immunity gives temporary protection by transfer of certain immune substances from resistant individuals.
An example of passive immunity is passing of antibodies from dam to calf via the colostrum (first milk after calving). This transfer only occurs during the first few hours following birth. Research from the USDA station in Nebraska has indicated that successful transfer of passive immunity (during the first day of life) enhances disease resistance and performance even through the feedlot phase.