The serum protein patterns in mares before and after foaling were examined. A fall in the serum globulins, particularly the γ-globulin fraction, detected about 2 weeks before parturition, was attributed to the selective concentration by the mammary gland of immune proteins and specific antibody from the blood for colostrum formation. After parturition the levels of protein and antibody in colostrum fell rapidly as the foal was suckled, and by 12 to 15 h. they were only 10 to 20 per cent. of their original concentration. All the foals examined were agammaglobulinaemic at birth. The trace levels of antibody present before suckling in foals born to hyperimmune dams, were far too low to be of any protective value. The foals rapidly acquired passive globulins by absorption of colostral proteins from the small intestine. The antibody levels attained were somewhat lower than those of the dams' serum at parturition. The passive γ-globulin and specific antibody (Cl. welchii type A antitoxin) declined steadily from 24 h. of life and by 3 weeks of age their levels had been halved. The antitoxin continued to fall reaching a barely detectable level by 4 months. Active immunity was demonstrated by the onset of autogenous γ-globulin production by the foal. In the colostrum-deprived foals autogenous γ-globulin was first detected after 2 weeks of life and in the foals which received colostrum from 4 weeks of age. Peak levels were reached sooner in the solostrum-deprived foals, but by 3 to 4 months the levels were fairly comparable in the 2 groups. The values for γ-globulin approximated those for adult horses and correspond to the peak levels of passive γ-globulin after birth. © 1974.
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