Weaned lambs, having a detectable level of maternal antibodies (1-2 units/ml) against C. perfringens type
D, showed protective antitoxin levels lasting for 29 days after receiving a single parenteral dose of 200 units/kg
hyperimmune serum. Lambs, having no maternal antibodies (<0,07 units/ml) to C. perfringens type D but
receivIng the same dose of hyperimmune serum, maintained protective antibody levels for only 21 days. Three
weeks after the titres fell below the minimum protective level of 0,15 units/ml, both these groups were treated
again in the same manner. The passive immunity conferred in both groups now lasted for 42 days. When the
hyperimmune serum was administered to lambs already immunized by vaccination, a slight increase was noted
in the antibody titre.
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