The antibodies found in the blood of a pregnant cow that are eventually transferred into the colostrum were all derived by the immune system of that cow in response to foreign substances to which the cow had been exposed during its lifetime.  These foreign substances include the various vaccines administered to protect the animal against different potential disease-causing microorganisms; clinical and non-clinical contagious infections experienced as a result of contact with other members of the herd, including microorganisms present in their excrement; and microorganisms vectored from handling and contact with equipment and other species.

The manufacturers of New Zealand colostrum powder state that the colostrum should only come from cows that are pasture-fed since that provides more antibody diversity. Although it is theoretically possible that some pathogens may be present in the soil and be vectored to the cow, this is highly unlikely since microorganisms that would ordinarily be found in clean soil and on grasses suitable for grazing would not be pathogenic to mammals – otherwise all of the animals in the herd would be sick most of the time.   Pathogens found in a pasture or any other environment would most likely be present as a result of animal excrement.

In the United States, it was recognized many years ago that open pasturing of dairy cows, including breeding and unsupported calf delivery in the pasture environment, was not conducive to good herd management practices and led to a higher incidence of disease; affected milk production volumes and the quality of milk. It also failed to provide the support necessary to assure that calves received adequate volumes of colostrum of sufficient quality to promote their proper development.  A large number of dairy farms in the United States have shifted to the use of so-called “dry lot” techniques that restrict the cows to little or no pasture grazing.  The animals are kept either inside of a structure or outside within clean, non-grass, fenced environments and fed a well-defined diet containing the required nutrients to assure effective development and maintenance of their health status. These areas can be cleaned routinely, either manually or automatically, to assure removal of excrement. The animals in such environments are frequently divided into groups reflecting the number of lactation cycles they have experienced and their average milk production capabilities.  This approach allows the dairy producer to more effectively control disease development and to recognize and separate animals with problems, regulate milking schedules, and control the quality and flavor of the milk.

The comparative merits of the different approaches to dairy herd management is reflected in the average milk yields reported by WHO for 2001. Dairy cows in New Zealand produced an average of 8,330 lbs. of milk per cow during 2001, while those in the United States averaged 18,139 lbs. per cow.