How is it different than mature breastmilk, and is there any real importance to baby having it? 

Colostrum is the first fluid that is available to baby after birth. It is usually very thick, yellowish, and creamy, whereas mature milk is often thin or watery looking and may have a blue tint to it. 

Many might believe that it is not overly important for baby to receive colostrum. Some don't realize or believe that colostrum is enough nourishment for a newborn.  Because of this, mothers are often urged to give their babies supplemental feedings, which are totally unnecessary and may result in problems in establishing breastfeeding. 

It may help to know that a newborn's tummy is very small, so baby doesn't need a lot of milk in the early days.  Many have probably heard that a baby's tummy may be about the size of a golf ball, but actually a newborn's tummy is even smaller!

As per the FAQ on Colostrum (wonderful visual in this article!) at the LaLeche League website:

"A 1 day old baby's stomach capacity is about 5-7 ml, or about the size of a marble. Interestingly, researchers have found that the day-old newborn's stomach does not stretch to hold more. Since the walls of the newborn's stomach stays firm, extra milk is most often expelled (spit up). Your colostrum is just the right amount for your baby's first feedings!

By day 3, the newborn's stomach capacity has grown to about 0.75-1 oz, or about the size of a "shooter" marble. Small, frequent feedings assure that your baby takes in all the milk he needs.

Around day 7, the newborn's stomach capacity is now about 1.5-2 oz, or about the size of a ping-pong ball. Continued frequent feeding will assure that your baby takes in all the milk he needs, and your milk production meets his demands."

Colostrum is packed full of important components, such as antibodies, leukocytes, (protective white cells), long-chained polyunsaturated fatty acids, protein (3 x greater than that of mature breastmilk), Vitamin A and a fair amount of Vitamin K. Colostrum is richer in minerals and lower in carbohydrates than mature milk.

Why are these things beneficial?

	Antibodies protect baby's mucous membranes (throat, lungs, and intestines), which are the places most likely to come under attack from germs in the fragile newborn infant
	White cells - (leukocytes) can destroy disease-causing bacteria and viruses
	Vitamin K helps protect baby against bleeding.
	Vitamin A is required for vision and is at it's highest the first week following birth
	Protein helps maintain baby's blood sugar, esp. for those who are at risk for low blood sugar

Colostrum plays a very important role in the baby's gastrointestinal tract. A newborn's intestines are very sensitive, and are permeable. Colostrum "coats" the gastrointestinal tract with a barrier, which mostly prevents foreign substances from penetrating, and possibly sensitizing a baby to foods the mother has eaten.

Colostrum is also a natural laxative, helping to move the meconium (the baby's first stool) out of the baby's system, helping reduce the incidence of jaundice in the newborn baby.