Calculating Serum IgG
The primary outcome predicted by CMC is the calf’s serum IgG concentration.
Serum IgG concentration depends principally on two quantities:
- The amount of IgG absorbed from colostrum.
- The volume of plasma into which that IgG is distributed.
Conceptually:
Because 1 g/L is numerically equivalent to 1 mg/mL, serum IgG can conveniently be expressed in either unit.
Step 1: Calculate IgG intake
For each feeding:
For example, 4 L of colostrum containing 50 g IgG/L supplies:
Step 2: Estimate IgG absorption
Suppose the predicted AEA for that feeding is 30%.
If the calf receives multiple feedings, CMC performs this calculation for each feeding and sums the absorbed IgG.
Step 3: Account for plasma volume
Suppose the calf has an estimated plasma volume of 3.65 L.
The predicted serum IgG concentration is therefore approximately:
Why calf size matters
Two calves may absorb exactly the same amount of IgG but have different serum IgG concentrations.
If one calf is smaller, the absorbed IgG is distributed within a smaller plasma volume, producing a higher concentration. A larger calf has a larger plasma volume and therefore a lower serum IgG concentration from the same amount of absorbed IgG.
This is why birth weight is an important input in CMC even though it does not directly determine how efficiently IgG is absorbed.
Monte Carlo calculation
CMC repeats these calculations independently for every simulated calf.
Each calf may have a different:
- Birth weight
- Colostrum IgG concentration
- Amount fed
- Feeding age
- Predicted AEA
- Plasma volume
The resulting serum IgG values form the simulated population used to calculate means, distributions, and the percentage of calves achieving selected passive-transfer targets.
