Perinatal studies in Equidae with special reference to passive transfer of immunity.
This work represents a study of aspects of passive immunityand the
method of its transmission to the Dewly born foal.
All the foals examined were agammaglobulinaemicat birth. Traces of
antitoxin, too low to be of any protective value, were present in foals
born to hyper immune dams. The foals rapidly acquired passive y globulbin
by absorption of colostral proteins from the small intestine. The antibody
levels attained were somewhatlower than those of the dams' serum at
parturition. The passive y globulin and anti toxin declined steadily after
24 hours and br three weeks at age their levels bad been halved. The
duration of demonstreble passive immunity did not extend for more than
four months of life.
The development of active immunity began within the first month of
life. Autogenous y globulin was detected after two weeks in the colostrum
deprived foals. In foals which received colostrum, y globulin levels approaohing
those for adult horses were detected by about four months of age.
The mechanism of absorption of colostral proteins was by uptake into
the epithelial cells of the small intestine and transfer via the lacteals
to the systemic oirculation. The intestine was apparently non-selective
in its absorption of maoromolecules. The efficiency of absorption three
hours after birth of labelled PVP, a synthetic polymer of similar molecular
size to y globulin, was shown to be 22% of the total dose. There followed
a linear decline in efficiency of absorption with age to the lowest recorded
levels at 20 hours. By 24 hours of life the intestinal epithelium was
no longer permeable to marker antibody.
Examination of the colostral proteins after absorption revealed that
the high molecular weight component, y globulin, was retained in the foal's
circulation, but that the smaller size milk proteins were excreted in the
urine. This neonatal proteinuria persisted only during the period of