Serum Total Protein- A Tool For Evaluating Colostrum Protocols

Serum Total Protein- A Tool For Evaluating Colostrum Protocols

Serum Total Protein (STP) is the measure of total protein found in the blood and is a good indicator of IgG obtained by passive transfer from colostrum in the young calf. This allows STP to be a reliable on farm method for evaluating the success of a colostrum program.

New recommendations state that ideal passive transfer results in the majority (~70%) of calves sampled showing an STP of 5.8 g/dL or greater, or a Brix reading of at least 8.9% or more. These values translate to a minimum IgG level of 18 g/L.  



Work with your veterinarian to obtain samples by jugular blood draw from calves 1-7 days of age. The sample can then be spun in a centrifuge for a few minutes or allowed to sit for 12-24 hours until the blood plasma coagulates at the bottom and serum separates to the top. Serum can then be pipetted onto the lens of a refractometer to get a reading.  

Routine sampling of STP can give some insight into the success of a colostrum program. If STP values are in the ideal range, then no changes need to be made. If STP values are low, then more investigation needs to be made.

Consider evaluating the following when exploring changes that might need to be made.

-Colostrum Quality

-Colostrum Amount

-Timeliness of Receiving Colostrum 

-Colostrum Cleanliness

-Equipment Cleanliness

-Environmental Cleanliness

-Difficult Birth

-Other stressors 



Evaluation of STP is a fairly economical procedure that can be done on farm. It’s something your veterinarian can do for you, or something that can even be done by yourself or a trained employee.

Your veterinarian should have all the equipment needed and is a great resource to get you started. If it’s something you want to do yourself, then you will at least need to invest in needles, blood collection vacutainer tubes, disposable pipettes, and a serum refractometer. A centrifuge is also handy but is a costly piece of equipment. You will need to determine if that investment is necessary for you or not. 



There are some limitations when it comes to using STP as a tool for evaluating passive transfer.

1. STP is not a good indicator of passive transfer when using a colostrum supplement or replacer. The ratio of fat to protein and IgG to protein in a supplement or a replacer is different than in fresh maternal colostrum, resulting in inaccurate results on the refractometer.

2. Dehydrated calves have reduced blood volume making protein more concentrated. STP results will be falsely elevated and not reliable in evaluating IgG levels. (>8 g/dL)

3. STP does not measure any other immune components of the blood. As we learn more and more about the impact that colostrum has on the microbiome and on gut development, in the future we may find it valuable to measure more than just IgG to gain a better understanding of the immune status of the animal.

4. Calves experiencing an inflammatory immune response from scours or respiratory illness will show elevated STP. (>7.5 g/dL)

At this point in time evaluating STP is the most economical and useful on farm tool used to help assess the success of colostrum programs and gives us an idea of the immune status of the animal. 

The great thing about science is that we are always learning new things and developing new technologies to help us be more proactive. As we learn more about the microbiome and its impact upon the immune system, we may look for new technologies in the future that will tell us more about the animal's immune status other than just IgG. 

Written by: Mariah Gull, M.S.


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