Passive Transfer & Prove the Colostrum Worked
Grades serum IgG
Grade a calf's passive immunity from serum IgG, total protein or Brix against the 2020 consensus bands, then back-solve the litres of colostrum to feed to hit the 150–200 g IgG target before the gut closes.
Assess & plan colostrum
Next: marginal transfer — tighten the protocol: feed 6.67 L within the first hour using colostrum testing ≥22% Brix, and use clean equipment. Your current colostrum is too dilute to hit the target in one feed — split it or use replacer.
Categories: Excellent ≥25 g/L serum IgG / STP ≥6.2 / Brix ≥9.4; Good 18–24.9; Fair 10–17.9; Poor (FPT) <10 (Godden, Lombard et al., consensus J. Dairy Sci. 2020). Target ≈150–200 g IgG, ~10% of body weight, within 6 h. Absorption falls from ~35% at birth toward gut closure by 24 h. Colostrum IgG estimated from Brix — confirm with a tested batch.
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Passive transfer — key facts
- Excellent
- serum IgG ≥ 25 g/L · Brix ≥ 9.4%
- Good
- 18–24.9 g/L · Brix 8.9–9.3%
- Fair
- 10–17.9 g/L · Brix 8.1–8.8%
- Poor (FPT)
- < 10 g/L · Brix < 8.1%
- IgG target
- 150–200 g first feeding
- Volume
- ≈ 10% of body weight within 6 h
- Good colostrum
- ≈ 50 g/L IgG ≈ 22% Brix
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Passive-transfer categories & herd goals
| Category | Serum IgG | Total protein | Serum Brix | Herd goal |
|---|---|---|---|---|
| Excellent | ≥ 25.0 g/L | ≥ 6.2 g/dL | ≥ 9.4% | >40% |
| Good | 18.0–24.9 g/L | 5.8–6.1 g/dL | 8.9–9.3% | ~30% |
| Fair | 10.0–17.9 g/L | 5.1–5.7 g/dL | 8.1–8.8% | ~20% |
| Poor (FPT) | < 10.0 g/L | < 5.1 g/dL | < 8.1% | <10% |
Colostrum absorption efficiency by age
| Age at first feeding (h) | Apparent absorption efficiency |
|---|---|
| 0 h | 35% |
| 2 h | 34% |
| 4 h | 32% |
| 6 h | 30% |
| 8 h | 26% |
| 12 h | 18% |
| 18 h | 10% |
| 24 h | 4% |
Source: consensus recommendations on passive immunity in dairy calves (Lombard, Godden et al., J. Dairy Sci. 103:7611, 2020) and colostrum-management reviews (Godden 2008/2019). Colostrum Brix→IgG and absorption curves are field-calibrated estimates.
Two questions, one calf, one short window
A newborn calf is born with almost no circulating antibody — it must absorb immunity from colostrum in the first hours of life, and the gut that lets whole antibodies through slams shut within a day. Get it right and the calf is protected through the risky pre-weaning weeks; get it wrong and you are looking at scours, pneumonia, stunted growth and dead calves. So there are really two questions: did the colostrum already fed do its job, and how much colostrum must the next calf get to be sure?
This tool answers both. Feed it a serum reading — IgG, total protein or Brix — and it grades the calf into the Excellent / Good / Fair / Poor bands of the 2020 industry consensus and plots it on the gauge. Then it back-solves the feeding side: from the colostrum's Brix it estimates IgG concentration, fills a feeder to the 150–200 g IgG mass target, and shows how much of that antibody actually reaches the blood at your chosen feeding age. Pair it with the Colostrum Feeding and Calf Milk Feeding tools for the full newborn-calf plan.
How to use it — 5 steps
- 1
Pick the serum test
Choose serum IgG, total protein or Brix — whichever your refractometer or lab reports.
- 2
Enter the reading
Type the calf's serum value to get the passive-transfer category and gauge position.
- 3
Enter colostrum quality
Add the calf's birth weight, the colostrum's Brix and the age at first feeding.
- 4
Read the plan
See the litres to feed, the IgG mass delivered and absorbed, and the timing penalty.
- 5
Feed and verify
Feed the recommended volume early; verify the next calf's status with a serum sample at 1–7 days.
Frequently Asked Questions
How do I tell if my calf has good passive transfer?+
Measure the calf's serum at 1–7 days of age (before vaccination) by IgG, total protein or Brix and compare to the 2020 consensus bands. Excellent is serum IgG ≥ 25 g/L (total protein ≥ 6.2 g/dL, Brix ≥ 9.4%); Good is 18–24.9 g/L; Fair is 10–17.9 g/L; and Poor — failure of passive transfer — is below 10 g/L. Enter your reading and the tool returns the category and plots it on the gauge.
How much colostrum should I feed a calf?+
Feed enough colostrum to deliver about 150–200 g of IgG at the first feeding, which is roughly 10% of the calf's body weight within 6 hours of birth. The exact volume depends on colostrum quality: at a typical 50 g/L IgG (about 22% Brix), 4 litres delivers 200 g; weaker colostrum needs more, and very weak colostrum cannot reach the target in one feed. The tool back-solves the litres for your colostrum.
What is failure of passive transfer (FPT)?+
Failure of passive transfer is when a calf absorbs too little colostral antibody, defined as serum IgG below 10 g/L (total protein below 5.1 g/dL, Brix below 8.1%). These calves have markedly higher risk of scours, pneumonia, poor growth and death. After the gut closes there is no way to fix it, so FPT is managed and, more importantly, prevented in the next calf.
Why does the timing of colostrum matter so much?+
The calf's gut absorbs whole antibodies for only a short window after birth, then progressively closes — apparent absorption falls from about 35% at birth toward near-zero by 24 hours. The tool shows the absorption efficiency at your feeding age and the percentage of IgG lost to delay. The same colostrum fed at 2 hours puts far more antibody into the blood than fed at 12 hours.
How do I convert serum total protein or Brix to IgG?+
Serum total protein and serum Brix are quick refractometer proxies that track IgG closely. The 2020 consensus anchors them: total protein 5.1 / 5.8 / 6.2 g/dL and Brix 8.1 / 8.9 / 9.4% line up with the IgG breakpoints of 10 / 18 / 25 g/L. The tool converts your chosen measure to an approximate serum IgG for the gauge marker.
What Brix means good-quality colostrum?+
On colostrum (not serum), a digital Brix reading of about 22% corresponds to roughly 50 g/L IgG, the usual cutoff for good colostrum to feed to a newborn. Below that the colostrum is dilute and you need more volume — or a colostrum replacer — to hit the IgG-mass target. The tool estimates colostrum IgG from the Brix you enter.
Can I always hit the IgG target in one feeding?+
Not with weak colostrum. If reaching 200 g of IgG would need more than about 12% of the calf's body weight in volume, one feeding is not feasible — the tool flags this. The fix is to split into two feedings (for example at 0 and 6–12 hours), use higher-quality colostrum, or fortify with a colostrum replacer or supplement.
Does this replace a serum or colostrum lab test?+
No — it interprets your readings and plans the feed, but the readings themselves come from a refractometer or lab. Use a calibrated Brix or total-protein refractometer on serum for status, and a Brix refractometer on colostrum for quality. The tool then turns those numbers into a category and a feeding plan.
What is the herd-level goal for passive transfer?+
The 2020 consensus recommends a herd distribution, not just avoiding failure: aim for more than 40% of calves Excellent, around 30% Good, no more than about 20% Fair, and fewer than 10% in the Poor (failure) band. Sampling a group of calves and tallying the categories is the way to audit a colostrum programme.
How is the absorbed IgG calculated?+
Absorbed IgG = colostrum volume × colostrum IgG concentration × absorption efficiency at the feeding age. For example 4 L of 50 g/L colostrum is 200 g fed; at 2 hours of age with about 34% absorption that puts roughly 68 g into the bloodstream. The tool shows both the IgG fed and the IgG absorbed so you can see the timing cost.
Are the figures precise?+
They are solid planning figures built on the published consensus thresholds and typical absorption curves. Real absorption varies with the individual calf, colostrum bacterial load and feeding method (tube vs bottle), and the Brix-to-IgG relationship is an estimate. Treat the result as a working plan, test a colostrum batch to confirm quality, and verify calf status with a serum sample.