What is the difference between 1st and 2nd cow colostrum? The first colostrum is harvested within the first 6-24 hours after the cow gives birth to her calf. Some people have requested the first colostrum before 6 hours. Our goal is to give the newborn animal first chance. Then we take the balance of the colostrum for bottling. The 2nd colostrum is usually harvested within 24-48 hours after the cow gave birth to her calf. After that the milk from the cow goes to regular milk. The first and second colostrum can vary in consistency & color depending on the genetics and also the season of the year.