Southern elephant seals: IgM concentration in milk of cows and serum of their pups

Serum and milk Immunoglobulin M (IgM) concentrations in 11 mother-pup pairs were measured in southern elephant seals (Mirounga leonina) throughout lac tation during 2 breeding seasons at King George Island. Samples were obtain ed sequentially throughout the suckling period (approximately 23 days). The IgM concentration was measured by single radial immunodiffusion on agarose plates. Milk IgM concentrations showed significant differences throughout lactation, with the highest concentrations on the Ist day (x = 989.7 mg/dL skimmed milk; SD = 433.2) followed by a sharp fall during the next 3-6 days of the suckling period. The ratio of milk IgM/serum IgM concentrations fro m mothers ranged from 0.21 to 21.92, with highest values in the Ist day of lactation (x = 8.25, SD = 5.4) and a decrease in concentration as lactation progressed. This was due to the fact that, throughout lactation, milk IgM concentrations fell while serum IgM values showed an increasing trend. Pups showed the lowest serum IgM values in the Ist day of the suckling period ( x = 13.0 mg/dL, SD = 4.3) with an increasing trend as lactation progressed. Despite the high IgM concentrations of milk at day 1 of lactation, by 1 we ek of age pups had serum IgM concentrations only slightly greater than at b irth. This suggests that much of this Ig was newly formed and little or no milk IgM was absorbed during the Ist week. Possibly, the function of ingest ed IgM is to provide local immunity in the pup's gut, during the first few days of postnatal life.