Page 748 - Veterinary Immunology, 10th Edition

secretory component, which may then prevent their absorption. The
VetBooks.ir duration of intestinal permeability also varies among species and

immunoglobulin classes. In general, permeability is highest
immediately after birth and declines after about 6 hours because of

the replacement of FcRn-bearing enterocytes by cells that do not
express this receptor. As a rule, absorption of all immunoglobulin
classes drops to a very low level after about 24 hours. Feeding
colostrum tends to hasten this closure, whereas a delay in feeding

results in a slight delay in closure (up to 33 hours). In piglets, the
ability to absorb immunoglobulins may be retained for up to 4 days
if milk products are withheld. The presence of the mother may be
associated with increased immunoglobulin absorption. Thus calves

fed measured amounts of colostrum in the presence of the mother
will absorb more immunoglobulins than calves fed the same
amount in her absence. In laboratory studies in which measured
amounts of colostrum are fed, there is a great variation (25%–35%)

in the quantity of immunoglobulins absorbed. Management should
ensure that foals or calves ingest at least 1 L of colostrum within 6
hours of birth.
Unsuckled mammals normally have very low levels of

immunoglobulins in their serum. The successful absorption of
colostral immunoglobulins immediately supplies them with serum
IgG at a level approaching that found in adults (Fig. 23.7). Peak
serum immunoglobulin levels are normally reached between 12

and 24 hours after birth. After absorption ceases, these passively
acquired antibodies decline through normal metabolic processes.
The rate of decline differs among immunoglobulin classes, and the
time taken to decline to non-protective levels depends on their

initial concentration. In calves the serum half-life of colostral-
derived IgG is about 28 days.

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