Passive Transfer & Prove the Colostrum Worked

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.