Dr. Fiona Maunsell, University of  Florida, College of Veterinary Medicine, in her paper entitled, "Cow Factors That Influence Colostrum Quality" presented at the Western Canadian Dairy Seminar in March, 2014, isolated these nine Take Home Points: (text below is directly from the seminar proceedings - I added bold emphasis, however)
 “High quality” colostrum is first-milking colostrum that contains at least 50 g/L of the antibody immunoglobulin G (IgG), contains a low concentration (<100,000 cfu/ml) of bacterial contaminants and is free of infectious disease agents.
Transfer of antibodies (especially IgG) from the blood of the cow into colostrum starts about 5 weeks prior to calving, and is maximal in the last 2 weeks before calving.
The older the cow, the better the colostrum – but there’s lots of individual variation! On average, first-calf heifer colostrum is lower in volume and IgG concentration than that from older cows. However, many heifers produce very good quality colostrum. Don’t automatically discard heifer colostrum; rather test and keep high quality colostrum from a cow of any parity.
Don’t automatically discard high volume first-milking colostrum if it was collected within a few hours of calving; colostrum should be tested and only discarded if low quality.
Discard bloody colostrum, colostrum from sick cows, from cows with clinical mastitis, from cows that are known to be infected with chronic diseases such as Johne’s disease or Mycoplasma, and from cows that
leak colostrum extensively prior to calving.
There is little evidence that nutrition, within the range of diets typically fed to dairy cows, has much influence on either the volume or quality of colostrum.
Heat stress may reduce the quality of colostrum, especially in heifers.
Dry period length should be at least 3-4 weeks to maximize colostrum quality.
Vaccinate cows against the calf diarrhea pathogens E. coli, rotavirus and coronavirus to maximize the amount of antibodies against these agents in colostrum. Make sure that cows are vaccinated at the appropriate time to optimize transfer of vaccine-induced antibodies into colostrum.
What a great collection of Take Home Points!