IgG is transferred from the bovine dam to calf in the colostrum. One measure of how successful this transfer has been is the presence of IgG in a calf's blood. Unfortunately, direct measurement of IgG by radial immunodiffusion (an accurate method) requires laboratory equipment and is expensive.

Research has been done to discover the relationship between IgG concentration in blood serum and total protein in blood serum (Tyler and others; White). They found that as total protein concentration goes up so does that of IgG. Because we can inexpensively measure serum total protein we can inexpensively estimate the IgG level in the calf's blood. While this way of estimating IgG levels is not perfect, it can be a workable tool for monitoring newborn management on-farm.

How do we sample it?

Sometime between day two and day seven of the calf's life a blood sample is drawn. We use red top blood collection tubes for collection. If we use the small three-ml tubes two ml of blood is enough. For the larger tubes, about five ml of blood is plenty. Usually, the blood is drawn from the jugular vein in the neck. Some people use a vacuum tube with a double-ended needle because the calves wiggle around so much. Once collected we want to process the sample so that the blood serum ends up on top and the blood solids on the bottom. If a centrifuge is available its use will give consistent and accurate results in only a few minutes. In the absence of a centrifuge gravity will give nearly similar results if the sample is allowed to sit undisturbed for about twenty-four hours (Fowler).

Caution: Calves that are dehydrated even a small amount will not test accurately. That is, their readings will be higher than actual levels. We try to sample blood within one to two hours after the second of two consecutive full fluid feedings. Feeding at 7:00 a.m. and sampling at 3:00 p.m. is likely to result in biased findings.

How do we measure blood serum total protein?

We wanted a procedure for measuring total protein that would require the least in investment. We chose refractometry. We purchased a refractometer in 1998 for around $300. All of the vet clinics have one in their labs, also. To do the test, a drop of serum is placed on the optical surface of the refractometer. A lid is lowered over the sample. The person looks through an eyepiece and reads the value from a scale etched on the lens. The round optical field is split with dark above and light below at the point on the scale corresponding with the grams of total protein per 100 ml of blood. With practice this determination is quick and accurate enough for on-farm evaluation of passive transfer of antibodies (IgG) from dam to calf via colostrum.