Timing of colostrum feeding is important because the absorption of immunoglobulin from colostrum decreases linearly from birth. "Intestinal closure" occurs when very large molecules are no longer released into the circulation and this occurs before the specialized absorptive cells are sloughed from the gut epithelium. In calves, closure is virtually complete 24 hours after birth, although efficiency of absorption declines from birth, particularly after 12 hours. Feeding may induce earlier closure, but there is little colostral absorption after 24 hr of age even if the calf is starved. This principle of timing of colostrum feeding holds true whether the colostrum is directly from the first milk of the dam or supplied by hand feeding the baby calf previously obtained colostrum.
Provide high risk baby calves (born to thin first calf heifers or calves that endured a dystocia) at least 2 quarts of fresh or thawed frozen colostrum within the first 6 hours of life and another 2 quarts within another 12 hours. This is especially important for those baby calves too weak to nurse naturally. Thaw frozen colostrum slowly in a microwave oven or warm water so as to not allow it to over heat. Therefore denaturation of the protein does not occur. If at all possible, feed the calf natural colostrum first, before feeding commercial colostrum substitutes.