Why Do I Need to Feed 200 grams of IgG?
Cabral, Chapman and Erickson (Univ. NH) published last week a review entitled "Colostrum supplements and replacers for dairy calves." (Prof. An. Sci. 29:449-456, Sept. 2013)
In it was a summary of 16 studies where colostrum and colostrum replacer products were fed to dairy calves. For each study estimates were made of the "apparent efficiency of absorption (AEA)." That is, for every 100g of IgG fed what proportion ended up in the plasma of the calf?
The range of AEA reported was from a low of 14.3 to a high of 51.1. The average value for all 36 experimental treatments in 13 studies for which AEA was reported was 32 (Median was also 32).
The arithmetic at this point is clear:
1. Feed 100 grams IgG, chances are high that 32 grams will end up in plasma.
2. Feed 200 grams IgG, chances are high that 64 grams will end up in plasma.
If we consider 50 grams in plasma as a lower threshold, then two quarts of colostrum that tests 50g/quart will not get us to our goal - strong immune protection for the newborn calf. However, four quarts of the same colostrum should push protection well above the desired minimum level.
Feeding one package of colostrum replacer containing 150g immunoglobulins may almost reach this lower boundary. Feeding enough colostrum replacer (e.g., two packets of 100g each) to get well above the threshold sounds like a better management practice.