The role of colostrum antibodies and the significance of antigenic competition in young lambs.

Young lambs were fed with a small amount of pooled colostrum and injected at either 1, 3, 6 or 12 weeks after birth with the antigen hen egg albumin (Ea). Five days before the Ea injection the experimental group were given a large dose of pooled vaccines (competing antigens). Blood samples were collected at regular intervals after the Ea injection. The results showed marked antigenic competition of Ea at both 6--and 12--weeks of age but the results were partially confounded by the presence of unexpected passive antibodies to Ea in the pooled fed. The experiment was repeated with a separate group of conventionally reared lambs given the same competing antigens but using human serum albumin (HSA) as the suppressed antigen. In this experiment the results differed since antibody concentrations and avidities to HSA were similar in 1, 6 and 12-week-old animals and there was no evidence for antigenic competition. The data presented illustrate the difficulties both of measuring immune responses in young ruminants and also of interpreting such results.