Immunoglobulins (IgG) in Colostrum, Explained Simply
Short answer: immunoglobulin G (IgG) is the main antibody in bovine colostrum. First-milking colostrum holds roughly 30–87 g of IgG per liter, versus well under 1 g/L in mature milk. To read a label, multiply the serving size in grams by the IgG percentage: 5 g at 20% IgG equals 1 g of IgG. Studies show a meaningful share of oral IgG survives digestion and stays active in the gut, but it is unlikely to be absorbed intact into the blood.
- What IgG is: immunoglobulins are Y-shaped antibody proteins, and IgG is the dominant class in colostrum. It is the number most brands use to signal quality.
- How much: about 30–87 g/L of IgG in bovine colostrum vs roughly 0.2–0.6 g/L in mature milk, and it falls quickly with every milking after calving.
- Label math: grams of IgG per serving = serving (g) × IgG % ÷ 100. Compare products by grams of IgG, not by percentage alone.
- Testing: labs typically measure IgG with Protein G affinity chromatography (HPLC), radial immunodiffusion (RID), ELISA or biosensors. Results can differ by method and lab.
- Digestion: human studies recovered about 19% (whole IgG concentrate) to 49% (hyperimmune concentrate) of ingested bovine IgG, still active, at the end of the small intestine.
What are immunoglobulins?
Immunoglobulins are Y-shaped proteins, also called antibodies, made by the immune system. Each one fits a particular target, such as a virus, bacterium or toxin, much like a key fits a lock. Once bound, antibodies can neutralize the target or flag it for removal. Humans and cattle both produce several classes, named by letters: IgG, IgA, IgM, IgE and IgD.
IgG is the most abundant antibody in blood and by far the dominant immunoglobulin in bovine colostrum, mostly as the subclass IgG1. That is why colostrum products are marketed around their IgG content. Bovine IgG can bind a wide range of human pathogens and some allergens in laboratory studies, which is the basis of most of the interest in it as a supplement (Ulfman et al., 2018).
Why so much IgG? Calves are born without antibodies passed through the placenta, so they depend almost entirely on colostrum in their first feeds. Nature concentrates IgG heavily in this early milk for that reason.
How much IgG is in colostrum vs milk
The difference between colostrum and regular milk is huge, and IgG drops with each milking after calving:
| Sample | IgG (g per liter) | Source |
|---|---|---|
| Bovine colostrum, range reported in reviews | 30–87 g/L (IgG1 34–87 g/L) | Playford & Weiser, 2021 |
| U.S. dairy survey, first colostrum | mean 74.2 g/L (5th–95th percentile 24.9–130.2) | Godden et al., 2019 |
| First milking (classic reference values) | 32 g/L | Godden et al., 2019 (Table 1) |
| Second milking | 25 g/L | Godden et al., 2019 (Table 1) |
| Third milking | 15 g/L | Godden et al., 2019 (Table 1) |
| Mature (whole) milk | about 0.2–0.6 g/L | Ulfman 2018; Godden 2019; Playford 2021 |
Two practical points follow. First, timing matters: in dairy research, colostrum IgG fell by 3.7% for each hour that the first milking was delayed after calving (Godden et al., 2019). Second, there is wide natural variation from cow to cow. On farms, colostrum with at least 50 g/L of IgG (or a Brix reading of at least 22%) is considered "high quality."
How does that translate to a powder? Liquid first-milking colostrum is about 24% solids. At 30–87 g/L of IgG, the dried solids would be very roughly 13–36% IgG before any losses. That is consistent with the 15–25% range most quality powders list. Labels claiming 40% or more imply a concentrated or fractionated product and should come with a test certificate. Our IgG percentage guide covers what to expect.
Converting a label IgG % into grams per serving
The IgG % on a label tells you what share of the colostrum powder is IgG by weight. To know how much you actually get, you need the serving size too:
Grams of IgG per serving = serving size (g) × IgG % ÷ 100
Worked example. A powder lists "25% IgG" and a serving size of one 6 g scoop:
- Convert the percentage to a decimal: 25% = 0.25.
- Multiply by the serving: 6 g × 0.25 = 1.5 g of IgG (1,500 mg) per scoop.
- To compare cost, take the whole tub. A 300 g tub at 25% contains 75 g of IgG. If it costs $45, that is $45 ÷ 75 = $0.60 per gram of IgG.
Now compare three hypothetical products:
| Product | Label IgG % | Serving | IgG per serving |
|---|---|---|---|
| A: powder | 25% | 6 g scoop | 6 × 0.25 = 1.5 g |
| B: powder | 20% | 2 g scoop | 2 × 0.20 = 0.4 g |
| C: capsules | 40% | 2 × 500 mg = 1 g | 1 × 0.40 = 0.4 g |
Product C has the highest percentage but delivers the same IgG as Product B, and less than a third of Product A. Three label details to check:
- Is the % of IgG or of "immunoglobulins"? Total immunoglobulins include IgA and IgM, so that figure will be higher than IgG alone.
- Is the % of the colostrum or of the whole product? In blends and flavored products, the colostrum may be only part of each serving. Multiply by the amount of colostrum, not the full scoop.
- Is it a minimum or a typical value? "Standardized to a minimum of 20%" is more useful than a vague "high IgG."
More examples are in what IgG % should colostrum have and how to read a colostrum label.
Shopping for colostrum? Our own brand is BIOMIXA grass-fed colostrum powder, direct from the maker.
How IgG is measured
The IgG number on a label is only as good as the test behind it. A 2007 review of IgG analysis in milk, colostrum and supplements groups the methods into separation-based and immune-based techniques (Gapper et al., 2007):
| Method | How it works | Where it is used |
|---|---|---|
| Protein G affinity chromatography (HPLC/LC) | IgG binds selectively to a Protein G column, is washed off and is measured by UV absorbance against an IgG standard | The most common method for colostrum powders traded on IgG content |
| Radial immunodiffusion (RID) | A sample diffuses into a gel containing anti-IgG antibodies. The diameter of the ring that forms reflects the IgG concentration. | The reference method for calf serum; also used in research on colostrum and digestion |
| ELISA | Antibody-based assay with a color readout | Research and some quality control |
| Optical biosensor (surface plasmon resonance) | Label-free binding measurement on a sensor chip | Used for IgG, lactoferrin and other minor milk proteins |
| Brix refractometer | Measures total solids as a proxy for IgG | Quick on-farm screen, not a label assay |
Protein G affinity LC was tested in an AOAC collaborative study across 11 laboratories (Abernethy et al., 2010). Labs agreed within themselves to about 2–4% (repeatability), but results between labs varied by about 6–19% (reproducibility). A key step is removing casein at pH 4.6, because casein can otherwise inflate the IgG result. Separate studies compared the method with RID, biosensor and reversed-phase LC (Copestake et al., 2006).
What this means for you: a difference of a couple of percentage points between two labels, such as 25% vs 27%, is within normal testing variation. Ask brands for a certificate of analysis that names the method and the lab. Our third-party testing guide explains what a good certificate looks like.
Does IgG survive digestion?
This is the central, honest question. IgG is a protein, and the stomach is designed to break proteins down. Bovine IgG turns out to be more resistant than most milk proteins, and part of it reaches the lower small intestine still active:
| Study | Design | How much IgG survived |
|---|---|---|
| Roos et al., 1995 | 7 healthy adults drank a 15N-labeled bovine immunoglobulin concentrate. Fluid was sampled at the end of the small intestine, and IgG was measured by RID. | About 19% of ingested IgG (and IgM) recovered still immunologically active. IgA was not detected. |
| Warny et al., 1999 | 6 people with an ileostomy took 5 g of a hyperimmune bovine colostrum concentrate (2.1 g IgG). | On average 49% of the IgG was recovered, still able to neutralize the target toxin. Antacids or omeprazole did not increase this. |
| Ulfman et al., 2018 (review) | Summary of studies measuring bovine IgG in stool | Recovery ranged from trace amounts (0.01%) up to 50%, depending largely on study methods |
Two more findings are useful. In the Warny study, IgG survived better in people whose food moved faster from mouth to the end of the small intestine (68% vs 36%). Enteric-coated capsules often passed through without fully opening, so "enteric coating" is not automatically an upgrade. Reviews agree that bovine IgG is unlikely to be absorbed into the bloodstream intact (Playford & Weiser, 2021). Any benefit in adults most likely happens inside the gut, for example by antibodies binding microbes or toxins there. See our colostrum and gut health overview.
What the evidence suggests and its limits
Researchers have studied colostrum and its immunoglobulins for several possible roles. Read these cautiously: colostrum is a dietary supplement, not a treatment, and it is not proven to cure, treat or prevent any disease.
| Area studied | State of evidence |
|---|---|
| Gut barrier under exercise stress | Several small, placebo-controlled trials show a smaller rise in gut permeability. Encouraging but small. |
| Gut and digestive comfort | Limited human data; quality and size vary |
| General immune support | Mechanistically plausible. Human results are mixed, and study designs vary too much for firm conclusions (Ulfman et al., 2018). |
| Hyperimmune colostrum against specific microbes | Specialized products made from immunized cows; not the same as regular supplements |
Across these areas, study sizes are often small, products differ widely in IgG content, and independent replication is limited. You can read a fuller, hedged overview on our benefits page.
How IgG content varies between products
Two colostrum supplements can differ dramatically in their actual IgG, depending on:
- Collection timing. First-milking colostrum is richest. IgG roughly halves by the third milking.
- Processing. Gentle, low-heat methods aim to preserve fragile proteins, while high heat can denature antibodies. Defatting concentrates protein, so it can raise the IgG %.
- Labeling honesty. Some labels state a guaranteed minimum IgG % with a named test method; others are vague.
If a product's IgG matters to you, look for a stated percentage, a serving size that delivers a useful amount in grams, and third-party testing. Format plays a role too. Our powder vs capsules comparison shows why capsules usually deliver far less IgG per day.
Practical takeaways
- IgG is the main antibody in colostrum, and colostrum is naturally rich in it because newborn calves depend on it.
- Judge products by grams of IgG per serving and cost per gram of IgG, not by the percentage alone.
- A meaningful share of IgG survives digestion, but any effect is likely local to the gut.
- Evidence for specific benefits is preliminary and should be read with caution.
For dosing and who should be careful, see dosage and safety. People who are pregnant, immunocompromised or allergic to dairy should speak with a healthcare professional first.
Frequently asked questions
What is IgG in colostrum?
IgG (immunoglobulin G) is the main antibody in bovine colostrum. It is a Y-shaped protein that binds specific microbes and toxins. Brands use the IgG percentage as their main quality marker.
How much IgG is in colostrum compared with milk?
First-milking bovine colostrum typically contains about 30–87 g of IgG per liter, while mature milk contains roughly 0.2–0.6 g/L. IgG falls sharply with each milking after calving.
How do I calculate grams of IgG per serving?
Multiply the serving size in grams by the IgG percentage and divide by 100. For example, a 6 g scoop at 25% IgG gives 1.5 g of IgG; two 500 mg capsules at 40% give 0.4 g.
Does IgG survive digestion?
Partly. Human studies recovered about 19% to 49% of ingested bovine IgG, still active, at the end of the small intestine. It is unlikely to be absorbed into the blood intact, so any effect is thought to happen in the gut.
How is IgG in colostrum measured?
Most supplement testing uses Protein G affinity chromatography (HPLC). Radial immunodiffusion (RID), ELISA and optical biosensors are also used. Results vary somewhat between methods and labs, so ask for a certificate of analysis that names the method.
Is a higher IgG percentage always better?
Not on its own. A high percentage in a tiny serving can deliver less IgG than a moderate percentage in a full scoop. Compare grams of IgG per serving and cost per gram, and be skeptical of claims above 40% without test results.
What IgG percentage should colostrum have?
Most quality colostrum powders list roughly 15–25% IgG, with 20% a common baseline. See our IgG percentage guide for a full buying benchmark.
Sources
- Playford RJ, Weiser MJ. Bovine Colostrum: Its Constituents and Uses. Nutrients. 2021;13(1):265. PMC7831509
- Godden SM, Lombard JE, Woolums AR. Colostrum Management for Dairy Calves. Veterinary Clinics of North America: Food Animal Practice. 2019;35(3):535–556. PMC7125574
- Ulfman LH, Leusen JHW, Savelkoul HFJ, Warner JO, van Neerven RJJ. Effects of Bovine Immunoglobulins on Immune Function, Allergy, and Infection. Frontiers in Nutrition. 2018;5:52. PMC6024018
- Gapper LW, Copestake DE, Otter DE, Indyk HE. Analysis of bovine immunoglobulin G in milk, colostrum and dietary supplements: a review. Analytical and Bioanalytical Chemistry. 2007;389(1):93–109. PubMed 17579844
- Abernethy G, Otter D, Arnold K, et al. Determination of immunoglobulin G in bovine colostrum and milk powders, and in dietary supplements of bovine origin by protein G affinity liquid chromatography: collaborative study. Journal of AOAC International. 2010;93(2):622–627. PubMed 20480910
- Copestake DE, Indyk HE, Otter DE. Affinity liquid chromatography method for the quantification of immunoglobulin G in bovine colostrum powders. Journal of AOAC International. 2006;89(5):1249–1256. PubMed 17042172
- Roos N, Mahé S, Benamouzig R, et al. 15N-labeled immunoglobulins from bovine colostrum are partially resistant to digestion in human intestine. Journal of Nutrition. 1995;125(5):1238–1244. PubMed 7738684
- Warny M, Fatimi A, Bostwick EF, et al. Bovine immunoglobulin concentrate-Clostridium difficile retains C difficile toxin neutralising activity after passage through the human stomach and small intestine. Gut. 1999;44(2):212–217. PMC1727384
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