Effects of preventing periparturient hypocalcemia in cows by parathyroid hormone administration on hematology, conglutinin, immunoglobulin, and shedding of Staphylococcus aureus in milk.

The effects of hypocalcemia at parturition on concentrations of serum immunoglobulin and conglutinin, number of bacteria shed into milk, and leukograms of dairy cows were investigated from -4 wk prepartum to 4 wk postpartum. Ten healthy multiparous Holstein cows were fed a high calcium diet to induce hypocalcemia at parturition. Five cows received intramuscular parathyroid hormone to prevent hypocalcemia at parturition. All cows experienced a leukopenia (attributable to an absolute and relative neutropenia) during the 1st wk after calving, decreased serum conglutinin activity during the first 3 wk postpartum, and decreased concentration of serum IgG1 during the 3 wk before calving. At parturition, a large increase in organisms was found in foremilk (1000 to 10,000 times more than prepartum values). Neither the hematological changes nor the decreased immunoglobulin concentration was influenced by hypocalcemia or the development of milk fever. This implies that the degree of hypocalcemia observed did not have a large or irreversible influence on bacterial infection, hematological, or humoral immunity changes in periparturient cows.