Concentration of IgG in colostrum varies according to many factors, including a cow’s disease history, volume of colostrum produced, season of the year, and breed, says a University of Pennsylvania paper by Jud Heinrichs and Coleen Jones. The paper notes that IgG levels vary widely from one cow to the next and range from less than 20 to over 100 mg/mL.

The difference between 20 and 100 mg/mL of IgG in colostrum can mean the difference between failure and success in passive transfer of immunity, and colostrum containing 50 mg/mL or more of IgG is considered to be a high quality feed for newborn calves (see click on dairy nutrition and then Colostrum Management Tools).

This is nothing new to veterinarians, and probably many of your clients. But as your clients try to streamline protocols and do the best they can with colostrum management, this becomes a prime opportunity for you to help them do a better job.

Using the right tools
Of course the best way to estimate colostrum quality is using a quantitative method such as a ColostrometerTM or Brix refractometer. “It’s better to measure than guess,” says calf expert Sam Leadley, PhD, Attica Veterinary Associates, P.C., Attica, N.Y.

A Colostrometer, which costs about $40, measures specific gravity as a means of estimating antibody concentration. A Brix refractometer (about $70) measures solids level as a means of estimating antibody concentration. “Look for a value of 22 or greater to show an antibody concentration of 50 mg/mL or greater,” explains Leadley. “Thicker and more yellow colostrum will tend to have a rather ‘fuzzy’ line between the dark and light parts. Don’t let this frustrate you too much. I just estimate about where the middle of the ‘fuzz’ falls and assign a value.”

Leadley says in all of the samples he’s checked with a refractometer it was quite easy to pick out the low-quality samples. “They were well down in the 15–16 range.”

When’s the best time to test?
Get the most out of colostrum testingLeadley says colostrum quality can be checked immediately upon collection or after refrigeration, but there are some things to keep in mind. Assuming the on-farm practice is to collect colostrum in a milker bucket from one cow (not combined with other cows’ colostrum), Leadley feels the best time to do a quality (antibody concentration) check is immediately post-collection. “If I know the quality I can make a better decision about either feeding or storing the colostrum,” he says.

Leadley gives an example of post-testing use of colostrum on small and large dairies example. For example, on a 50-cow dairy, if it’s high-quality colostrum, it needs to be fed. “If it’s poor-quality colostrum, I still feed it and give the calf a colostrum supplement, too. Or, I might feed one package of colostrum replacer right away followed by two quarts of the poor-quality maternal colostrum. The reason I recommend feeding both replacer and colostrum in these settings is to capture the white blood cells in the fresh maternal colostrum as well as the ‘less well-defined’ components.”

For a large farm such as a 5,000-cow dairy, Leadley says the calving unit staff checks colostrum as it is collected, and the good stuff is chilled and refrigerated for first feedings. “My observations on these dairies is that in order to standardize procedures, all newborns are fed warmed-up fresh colostrum and all colostrum coming from the milking stall(s) goes into a ‘test, chill and store’ routine.” Depending on supply, lower quality colostrum may be discarded or stored for second feedings.

Leadley says once the colostrum is outside the cow’s udder, he doesn’t believe antibody concentrations are going to change in a measurable way. “I have checked split samples of colostrum with Brix refractomers where I have had the colostrum at 4°C, 16°C and 37°C. There were the same values at all three temperatures.” Thus, he says, colostrum could be tested right after collection or out of the refrigerator.

In contrast, we know that when using specific gravity as a proxy for antibody concentration (i.e., Colostrometer) the calibration temperature is 23°C. The instructions that come with the original Colostrometer explain how to estimate “true” values when checking “cold” or “hot” colostrum. There is a chart available at The Pennsylvania State University calf website (see link above) where given a known temperature and current Colostrometer reading, one can determine a “temperature-corrected” value. Thus, says Leadley, colostrum could be tested right after collection or out of the refrigerator.

“Remember that you trap air in the colostrum when you fill your bottle or tube,” Leadley notes. “Extra air lowers the specific gravity so the readings show lower than actual concentration. Let it sit for four to five minutes, then take your reading.” Leadley adds that in warm colostrum, a Colostrometer will slightly underestimate antibody concentration. So, if it reads either green or yellow the colostrum is okay and is 50 mg/mL or greater.

Care for the Brix
Leadley recommends that if you are checking more than one sample to be sure to rinse and dry the optic surfaces of the Brix refractometer between samples. To use a Brix refractometer, a few drops of colostrum are placed on the prism and the sample cover is lowered. The refractometer is then held up to a light source, the instrument should be held perpendicular to the light, and the Brix value is read at the line between the light and dark areas that appear on the scale. It is a good practice to check the calibration of the refractometer occasionally. The manufacturer should provide instructions on checking and adjusting the calibration, but distilled water should produce a reading of zero when the instrument is properly calibrated.

“Remember that refractometers work by using a prism to split light rays,” he explains. “Thus, if the surface on which the sample is placed is not clean the light will not go through it to get an accurate reading. I think it is a ‘best management practice’ to keep the optic surfaces clean. Clearly, if you don’t get the optic surface quite clean you have no chance of getting an accurate estimate from one sample to the next. This is the same principle when we use a clinical refractometer to determine blood serum total
protein values.”

Leadley says since scratches on the surface can distort the passage of light rays, it is important to avoid abrasive cleaning materials. “That is why I like to flush the optic surface on my refractometer with water ASAP after taking my readings. If the optic surface looks the least bit cloudy I use a bit of dishwash detergent in the water to remove the fat film coming from colostrum. If I dry it off promptly then there is neither a film nor spots on the optic surface.”

With even a rough estimate of colostrum quality we can 1. sort colostrum so that the best is fed first, 2. supplement lower quality colostrum if it has to be fed, and 3. use a colostrum replacer when that is the preferred management alternative.

“I try to emphasize with producers that both the Colostrometer and Brix refractometer readings are only estimates of antibody concentration,” Leadley says. “Our real purpose in checking colostrum on-farm is to make better decisions about managing calf immunity.” 

Colostrometer and Brix refractometer tips
Your dairy clients need to use colostrum-measuring tools correctly to get the most out of their colostrum feeding programs. Two calf experts offer some tips and additional resources to help you help your clients do a better job.

Jim Quigley, PhD, offers these tips to help your clients more effectively use a Colostrometer.

* Allow a sample of colostrum to cool to room temperature.

* Float the colostrometer in the colostrum.

* If the Colostrometer indicates poor quality colostrum, do not feed it to calves during the first 24 hours. Save it for days 2 and 3.

* If the Colostrometer indicates high quality colostrum, then use the 18 lb rule (if the cow makes more than 18 lb (8.5 kg) of colostrum, the odds are < 50% that it will contain sufficient colostrum).

* If the colostrum passes the Colostrometer test and 18 lb rule, then feed it as soon as possible.

See more at, Calf Note #22 – Using the Colostrometer to Measure Colostrum Quality.

Brix refractometer
Sam Leadley, PhD, explains what to look for in a Brix refractometer reading for best colostrum results.

* The threshold value to remember is 22.

* Values above 22 are good. Use for first feeding.

* Values below 22 are not so good. Use for second or later feedings. Or, if it must be used for first feeding, give the calf a colostrum supplement.

* A reading above 22 estimates the antibody content is 50g/liter. That is where the top of the green line appears on a Colostrometer.

Quigley adds that refractometer is a more appropriate method for measuring colostrum quality than the Colostrometer, even though the Colostrometer is usually what producers have on hand. “A recent study conducted at Iowa State surveyed 67 dairy farms in 12 states, collecting more than 800 colostrum samples,” Quigley notes. “The researchers found that when colostrum is tested shortly after collection (and before storage in refrigerator or freezer), the predictability of a Brix refractometer was excellent — the r2 of regression with IgG measured by RID was > 0.80.”

See more on using the Brix refractometer at, click on Calf Facts and then “Colostrum Testing Using the Brix Refractometer.”