A calf is born immunodeficient because of the placenta that it develops in. This type of placenta, known as a epithelialchorial placenta, prevents blood from being exchanged between the mother and infant. This means that nutrients are able to diffuse across but the blood is kept separate in two pools: one for the mom and one for the baby. This separation prevents antibodies that are present in the blood of the dam -- or momma cow -- from being transferred to the blood of the calf. The end result is an immunodeficient newborn that is highly susceptible to pathogens or disease causing organisms.
Conveniently, cows have evolved to produce colostrum, a special type of milk produced immediately after they give birth. This colostrum is high in many nutrients that benefit newborn calves but another key component makes colostrum special: antibodies.
A dam’s colostrum actually contains the antibodies that could not be absorbed from the placenta in a form that can be absorbed by the calf via the first milk. The dam passes antibodies that she has collected over her lifetime along to her offspring when they consume this colostrum. This process is referred to as passive immunity.
In the wild, the mechanism for passing along this immunity via colostrum is pretty straightforward. The calf is born, stands up after about half an hour, then proceeds to nurse off its mother. In a modern dairy facility, the process gets a little more complicated. For various reasons, standard practice is to separate the cow and calf immediately following birth. Segregating the calf from its mother helps to reduce the likelihood of the calf being exposed to any pathogens during its immunodepressed state as well as enables the farmer to ensure the calf receives an adequate amount of colostrum.
Since the dam is no longer directly providing the colostrum, the first step is harvesting the colostrum from the dam. To do this, the cow’s teats are cleaned and disinfected and the colostrum is harvested using sterilized milking equipment. Then the colostrum can be fed to the newborn calf. For your average sized Holstein calf (the black and white ones), a gallon of high quality colostrum is typically administered.
On second thought, don’t feed that colostrum to your calf just yet; quality control is important.
The quality of colostrum is determined by the amount of antibodies contained within and can be measured on a farm utilizing either a colostrometer (basically a hydrometer) or a refractometer. A colostrometer measures the specific gravity, or density, of the colostrum and estimates antibody levels based on those readings. Colostrum is rated on a green, yellow, red scale indicating the approximate quality of the colostrum. A brix refractometer can also be used that utilizes the absorbance of a sample to estimate the antibody content of the colostrum. Originally designed to measure sugar content in liquids, these meters have been adapted to measure antibody content in colostrum.
At this point, the colostrum has been harvested cleanly and determined to be of high quality. Now comes the fun part: feeding the newborn calf.
Most newborn calves will readily suckle shortly after birth and can therefore be fed using a clean sanitized bottle with a nipple on it. It is recommended that a newborn Holstein calf receive a gallon of high quality colostrum within two hours of birth to ensure adequate blood antibody levels. When a newborn calf will not suckle, an esophageal feeder is used to make sure the calf gets the required amount of colostrum.
So, why do farmers work so hard to make sure the calf receives so much colostrum within 2 hours after being born? Well, antibodies are fairly large and in order to be utilized by the calf, the antibodies must be absorbed into the small intestine. In order for this to occur, the small intestine must be relatively porous. Soon after birth, pores in the small intestine that are present initially start to close up and the efficiency of antibody absorption rapidly decreases. After about 24 hours, antibodies are no longer absorbed effectively. For the immunodeficient newborn calf, it is imperative that it receive an adequate amount of high quality colostrum during the period in which the dam’s antibodies are able to be absorbed most efficiently. This ensures that the calf receives adequate passive immunity and helps to ensure a healthy life.
Heinrichs, J. Jones, C. Colostrum Management Tools: Hydrometers and Refractometers.
Quigley, J. Calf Note #22 – Using the Colostrometer to Measure Colostrum Quality
Bowen, R. Placental Structure and Classification.