Page 754 - Veterinary Immunology, 10th Edition

IgG level fails to reach 400 mg/dL, severe infections are assured
VetBooks.ir (Fig. 23.9).

FIG. 23.9 Immunoglobulin levels in newborn serum during the first
15 weeks of life indicating the relative contributions of maternal
antibody and antibody synthesized by the newborn animal.

Diagnosis of Failure of Passive Transfer

The success of passive transfer cannot be evaluated in a foal until 18
to 24 hours after birth, when antibody absorption is essentially
complete. Several assays for serum immunoglobulins are available

(Table 23.2). The most rapid and economic procedure is the zinc
sulfate turbidity test, which involves mixing a zinc sulfate solution
with foal serum. Zinc sulfate precipitates globulins and the amount
of precipitate is proportional to the immunoglobulin concentration.

In total failure of transfer, the reaction mixture remains clear. In
sera with an IgG level of more than 400 mg/dL, the mixture
becomes cloudy. As an alternative to visual inspection, the optical
density of the mixtures can be read in a spectrophotometer and the

IgG concentration read off a standard curve. The relative amount of
precipitate can also be read in a hematocrit capillary (immunocrit).
Similar techniques include precipitation by ammonium sulfate,
glutaraldehyde, or sodium sulfite.

TABLE 23.2

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