Natural maternal colostrum is the best form of colostrum for a calf. The colostrum is full of disease-fighting immunoglobulins (also called IgG.) These immunoglobulins provide calves with the immune protection they desperately need to fight off environmental pathogens and bacteria. The reason why it is SO important for a calf to get up and nurse well and quickly after birth is because there is a small window of time, that a calf can absorb these IgGs. The calf absorbs the IgGs (antibodies) by apical tubular system in the intestinal absorptive cells. These cells will slough off over the first several hours of life, after birth. By the time 6 hours have passed the calf is only able to now absorb approximately 50-60% of those IgGs. Total closure of this window happens within about 24 hours.
Most health Dexter calves are up on their feet within 30 minutes and nursing. A calf's first feeding should ONLY be colostrum with antibodies. Sometimes, things don't go well at a birth and panicked ranchers will try to feed the calf “something” if they don't have any colostrum on hand. It is a big mistake to feed the calf whole milk or other milk without antibodies first, because even if you feed them colostrum replacement later, the ability for that calf to absorb those are minimal due to the whole milk that was given.
Cow's colostrum quality: Typically a mature cow will produce high levels of antibodies than a first freshener heifer would. Many vets will recommend providing all pregnant cows, but especially bred heifers, with pre-calving vaccinations to boost that colostrum with ample antibodies. Colostrum production starts about 8 weeks before calving. It can take about 2-4 weeks for the body to react to a vaccination, in the production of heightened antibodies. So, on our ranch we give pre-calving vaccinations to our bred cows 12-8 weeks before calving dates.
Natural colostrum from the dam or at least a cow in that herd, is far better than any emergency replacement or supplement you can buy. It is just a fact. Each year we will save a small amount of fresh colostrum from our milk cows, to use in the event of an emergency. So far we have never had to use it but one day it will happen. However, what is your second best option if you do not have access to colostrum from your herd? I would be careful taking fresh colostrum from another herd as you do not know what those cows carry and the pathogens present are not the same as found in your herd.
There is colostrum replacement you can buy at your local feed store in a pinch or you can order some ahead of time and store it in your cattle medicine cabinet. If you buy online you can find replacements that may be far better than your local tractor supply brands. Below will be some places to buy from online vendors. Always follow the directions on the bag. A large breed calf of 80lbs would take in about 2 quarts every 12 hours, so adjust to fit your size Dexter accordingly.
Ask you veterinarian, but many will say you want to buy the Colostrum replacement with IgG amounts over 100g and the greatest % of IgG. This is not the time to be cheap! Buy the best stuff you can but know that you may not use it before it expires. It's a cost of doing business, as they say.
Above: Calf up and vigorously nursing in about 20 minutes. Dam encouraging the calf to head for the teats.