Passive transfer of immunity

Definition

Passive transfer is the absorption of maternal antibodies (mainly IgG) from colostrum across the newborn calf’s gut into its blood. Calves are born with almost no circulating IgG. The gut can only absorb these large molecules for about the first 24 hours, and absorption efficiency starts dropping within hours of birth.

Passive transfer is graded from a blood sample taken at 1–7 days of age, after absorption is complete and before the calf makes much antibody of its own. The tests are:

Serum IgG: the reference measurement (radial immunodiffusion, RID).
Serum total protein (STP): measured with an optical or digital refractometer, in g/dL.
Serum Brix: measured with a Brix refractometer, in %.

STP and Brix are cheap on-farm stand-ins for IgG.

The traditional single cutoff for failure of passive transfer (FPT) is serum IgG < 10 g/L. The 2020 US consensus replaced this pass/fail cutoff with four categories and a herd-level goal for each (below).

Formula

Herd-level prevalence per category:

% in category = calves tested in the category / calves tested × 100

Apparent efficiency of absorption (AEA), a research/troubleshooting measure:

AEA (%) = serum IgG (g/L) × plasma volume (L) / IgG fed (g) × 100
plasma volume (L) ≈ 0.09 × birth weight (kg)
IgG fed (g) = colostrum IgG (g/L) × volume fed (L)

LaTeX:

\mathrm{AEA} = \frac{[\mathrm{IgG}]_{\text{serum}} \times (0.09 \times \mathrm{BW_{kg}})}{[\mathrm{IgG}]_{\text{colostrum}} \times V_{\text{fed}}} \times 100

How to pull it in DC305

DC305 has no standard passive-transfer item. Herds record it in different ways:

A user-defined item on the calf, e.g. STP, TP or BRIX. Pull it with:
```
LIST ID BDAT STP FOR BDAT>-60 STP>0
SUM STP FOR BDAT>-60 STP>0
```
A remark on an event, e.g. a TP or BLOOD event with the value in the remark. Pull it with an EVENTS list over the date window. At least one herd keeps a saved command STP that lists events and technician this way: EVENTS ID BDAT MTECH\2SI.
Outside DC305: a calf-raiser app or spreadsheet.

The item or event name differs by herd. Look it up in that herd’s private dc305-vocab mapping before pulling, and report how many calves were tested next to the result.

[!VERIFY] DC305 syntax for listing an event’s remark values over a date window, so event-recorded STP can be summarized.

Typical range

Herd context: US dairy heifer calves (mostly Holstein), individual hutches or pens, sampled at 1–7 days old. These are the consensus categories and herd goals from Lombard et al. 2020:

Category	Serum IgG (g/L)	STP (g/dL)	Serum Brix (%)	Herd goal (% of calves)
Excellent	≥ 25.0	≥ 6.2	≥ 9.4	> 40%
Good	18.0–24.9	5.8–6.1	8.9–9.3	≈ 30%
Fair	10.0–17.9	5.1–5.7	8.1–8.8	≈ 20%
Poor	< 10.0	< 5.1	< 8.1	< 10%

[!VERIFY] Confirm each threshold and herd goal against Lombard et al. 2020, Table 1.

Under the older single cutoff (STP < 5.0–5.2 g/dL, i.e. FPT), well-run herds aim for < 10% FPT. NAHMS Dairy 2014 found roughly 12% of US heifer calves had FPT.

[!VERIFY] NAHMS Dairy 2014 FPT prevalence figure.

Inputs that drive passive transfer:

Colostrum quality: ≥ 50 g/L IgG, or ≥ 22% Brix on colostrum.
Volume: about 10–12% of body weight (around 4 L for a Holstein) in the first feeding, within 1–2 hours of birth.
Bacteria: total plate count < 100,000 cfu/mL.

[!VERIFY] Colostrum feeding targets (volume, timing, bacteria thresholds) per Godden et al. 2019.

Common mistakes

Sampling at the wrong age. Before 24 hours, absorption isn’t finished. After about 7 days, IgG has decayed and the calf’s own antibodies muddy the reading.
Testing dehydrated calves. Dehydration concentrates serum and inflates STP and Brix. Don’t sample scouring or dehydrated calves for monitoring.
Mixing up colostrum Brix and serum Brix thresholds. Colostrum is graded at ~22% Brix; serum uses 8.1–9.4%. They are different scales.
Sampling only sick calves, or only a convenient pen. Herd prevalence needs a consistent sample, e.g. every calf, or every calf born on set days.
Reporting only % FPT. Under the 2020 categories, a herd can have < 10% “poor” calves but few “excellent” ones, and still have morbidity problems.
Grading Jerseys and crossbreds on Holstein refractometer cutoffs without noting it. The STP–IgG relationship was validated mostly in Holsteins.
Recording the result on the dam instead of the calf, or in free-text remarks that can’t be summarized.