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The primary purpose of the experiments reported in this paper was to determine whether a powerful systemic antigenic stimulus, given at the time of mammary involution, would affect the level of specific antibody in milk secreted during the ensuing lactation. The results showed that a single systemic administration of antigen with adjuvant, during mammary involution, is an efficient means of inducing high titres of specific antibody in milk in the subsequent lactation. Furthermore, such antibody belongs mainly to the IgA and IgM classes of immunoglobulin. These results suggest that the antibody is produced locally in the mammary gland by sensitised cells of the lymphocyte-plasma cell series, which infiltrate the tissue during the early stages of mammary involution and then become sessile.

Antibody responses were measured in colostrum-fed (CF) and colostrum-deprived (CD) calves immunised at ages varying from birth to four months using a variety of antigens with and without adjuvant. In addition immunoglobulin production in CD calves over the same period was compared with that of CF calves. A marked unresponsiveness to antigens injected at birth was observed if maternal antibody specific for the antigen used was present in the circulation. However, significant responses to all antigens tested occurred in CD calves and also in CF calves immunised with an antigen (egg albumin) to which there was no maternal antibody. Since these responses were not as great as those in older calves immunised similarly it is clear that age was influencing the response. It was also found that subsequent responsiveness was not significantly enhanced or impaired by neonatal exposure to antigen. With respect to immunoglobulin production the results conclusively demonstrated that endogenous production occurred much earlier in CD calves than CF calves and even after 128 days the serum concentrations of IgG1 and IgA in CD calves exceeded those for CF calves. Thus it appears that the most important consideration in immunological responsiveness of neonates is not so much immaturity of the lymphoid system as the effects of maternal antibody on the cells in that system.

1. A technique is described for the collection of thoracic duct lymph from the grazing cow.2. The effects of continuing drainage of lymph were overcome by establishing an exteriorized lymphatico-venous shunt from which lymph and blood samples were obtained when required. The shunt functioned satisfactorily for periods of 10, 14 and 28 days in the three cows.3. The rate of lymph flow and concentration of lipids in the lymph were low during and immediately after the operation. Higher sustained levels of flow of 1.37 +/- 0.43 (S.D.), 1.88 +/- 0.40 (S.D.) and 1.90 +/- 0.45 (S.D.) 1./hr, for the dry and two lactating cows respectively, were observed during the period 3-9 days after the operation.4. More than 200% of the volume and 100% of the protein of the blood plasma compartment passed through the thoracic duct each day.5. Chlyomicron triglyceride comprised 50-70% and phospholipid 20% of the total lipid in lymph.6. The results indicated that at least 200 and 400 g of esterified fatty acid were transported daily in the lymph of the dry and lactating cows respectively.