Recommendations for feeding colostrum to newborn calves have changed considerably over the past several decades. Early recommendations were relatively simple: feed a fixed quantity of colostrum as soon as possible after birth. As our understanding of passive immunity improved, recommendations became more specific. Colostrum quality, usually expressed as IgG concentration, became important, and the amount of colostrum fed increasingly came to be expressed as a quantity of IgG rather than simply liters or quarts. More recently, recommendations have also considered calf body weight, age at feeding, additional feedings, and factors that may influence the efficiency with which IgG is absorbed.
These changes have improved our ability to describe what should happen to an individual calf. However, a colostrum program is implemented on a herd, not on a single “average” calf. Calves differ in birth weight, colostrum varies in IgG concentration, and feeding times and amounts are never perfectly uniform. Even when a herd follows a well-designed protocol, the biological and management variation among calves means that serum IgG concentrations will also vary.
This creates a different question from the traditional one of how much colostrum should be fed to a calf. The more useful herd-level question is: What distribution of passive immunity outcomes should we expect from a particular colostrum program?
Answering that question requires considering many sources of variation simultaneously. Simulation provides a practical way to do this. CMC was developed to combine current knowledge of IgG absorption with realistic variation in calves, colostrum, and management. By simulating thousands of individual calves, alternative feeding programs can be compared not only by their average outcome, but also by the proportion of calves likely to achieve—or fail to achieve—the desired level of passive immunity.
CMC represents the next step in colostrum recommendations: from prescribing a feeding for an individual calf to designing and evaluating a colostrum program for the herd.