Production of foetally stimulated lymphocytotoxic antibodies by multiparous cows

Serum samples were collected monthly from second gestation cows and examined for the presence of lymphocytotoxic antibodies. Of 25 cows studied 16 (64%) raised antibodies during or immediately after second gestation. Ten of these cows (40%) raised antibodies during gestation, some as early as 5 months before parturition. Reactors which had had first-gestation reactivity responded earlier, but had peak antibody titers no higher than cows without observable first gestation reactions. Cows with antibodies of similar specificity in the first two gestations responded earlier than those with different antibody specificities. Regardless of the time of first antibody detrection, peak titers were usually achieved during the first month postpartum. Antibody persistence increased with parity. Among cows of all ages sampled at random times, there was a linear relationship of serum reactivity to cow age.