IgG

This calf won't have to worry about failure of passive transfer, and adequate IgG levels.

Indications for performing this test: Evaluating serum IgG levels is a basic measure of passive transfer in the neonate. Because failure of passive transfer of colostral immunoglobulins is the major factor determining whether a neonate will get sick, it is an important management tool. The amount of circulating immunoglobulins in the neonate is the result of two factors: the amount of immunoglobulins present in the colostrum (further dependent upon concentration of immunoglobulin in the colostrum and the volume of colostrum consumed) and the efficiency of their absorption by the neonate. Serum IgG levels may also be measured in cases of suspected immunodeficiency that involve B lymphocytes.

Contraindications: none

Advantages: There are several tests available to evaluate serum IgG levels making this test relatively easy and cost effective.

Disadvantages: none

The Test: Several tests are available to assess serum IgG levels in the neonate.

Radial Immunodiffusion: Though this test is the gold standard, it is expensive and time consuming. It is available commercially, but due to expense and time, it is usually used in research settings and not in the field.

ELISA: An ELISA test exists for foal and piglets, but due to expense and time, this test is commonly not used in the field in any species.

Quantitative Zinc Sulfate Test: This is a relatively good test, but it requires proper instrumentation to run. Blood samples must be handled properly to ensure accurate results.

Serum Gamma-glutamyltransferase (GGT) Activity: GGT levels have been used to evaluate passive transfer status if other tests are not available. GGT levels are high in the colostrum of ruminants (not horses) and thus correlate relatively well with serum IgG concentrations. This test must be run quickly as the half-life of GGT is short and serum GGT activity falls significantly in the first week of life.

Serum Total Protein: Total protein levels can be measured very easily with a refractometer. Total protein gives an indirect measurement of the amount of immunoglobulins present, but there is a fairly good correlation between total protein levels and immunoglobulin levels.

Sodium Sulfite Precipitation Test: This rapid, easy to use test is most commonly used in the field to determine passive transfer status.

In foals, there is a new "foal-side" test to measure serum IgG in 10 minutes ( Idexx SNAP® foal ).

Test Interpretation: Much research has been done to determine what levels of IgG are protective. These studies sometimes come to different conclusions. General guidelines can be helpful though and are given below for the species in which these tests are most commonly used. Again, these are only guidelines. It is possible that an animal with low IgG levels will not get sick. It is also possible that an animal with complete passive transfer will get sick. These values are based on samples obtained from calves and foals in the first 12-48 hours of life. It becomes much more difficult to assess passive transfer status as an animal becomes older and passive immunity diminishes (see graph below).


Calves	Foals
IgG < 200 mg/dL: complete failure of passive transfer	IgG < 200 mg/dL: complete failure of passive transfer
IgG < 500 mg/dL: partial failure of passive transfer	IgG >400 but < 800 mg/dL: partial failure of passive transfer
IgG > 500 mg/dL: protection against septicemic disease	IgG > 800 mg/dL: protective against infectious disease
IgG >1000 mg/dL: more sufficient to decrease risks of infectious disease in most environments	Reference: Large Animal Medicine, Bradford P. Smith

Levels of immunoglobulin in serum during the first 15 weeks of life (normal).

This graphs show the relative contributions of maternal antibody versus antibody synthesized de novo by the newborn (a normal foal in this case).

Note the trough where passively acquired maternal antibody is waning while antibody synthesized by the foal is only beginning to increase. This may represent a period of increased susceptibility for some infections.

Question: How would you interpret a serum IgG level regarding adequacy of passive transfer if you sampled it after 5-6 weeks of age? Remember that in the absence of blocking maternal antibody, the newborn may begin to produce its own IgG at an earlier timepoint.

Figure from I.R. Tizard's Veterinary Immunology: An Introduction. 5th edition.
WB Saunders Co. 1996. Figure 19-6, page 245.