Colostrum is a source of energy and nutrients that is easy to digest.
It provides antibodies which will be the lamb's passive immune system until it has developed its own active immune system.
Colostrum has a laxative effect that helps to clean out the digestive tract.
Adequate colostrum intake is crucial for preventing lamb mortality and ensures that the lamb gets a good start in life. In most cases, newborn lambs will suckle on their own without intervention. However, where ewes have poor colostrum yield, mastitis, more than two lambs or lambs that are not sucking, intervention might be necessary.
Lambs should consume colostrum within the first six hours of life and at six hourly intervals thereafter, at a feeding rate of 50ml for every kilogram of body weight. Immunoglobulins in colostrum is protein-based and therefor very sensitive to temperature, so heating or thawing colostrum should be done with care, to not denature the protein. Rather store colostrum in small containers to speed up the thawing process and never heat colostrum in a microwave or in water that is too hot to immerse your hand into.
Watch Michael Gottstein from Teagasc, explain the importance of lambs receiving colostrum within the first six hours of life.
Reference: https://www.teagasc.ie/news--events/daily/sheep/the-3-important-roles-of-colostrum-for-newborn-lambs.php