Dynamics of serum immunoglobulin concentrations in sheep during pregnancy and lactation.

Monospecific antisera were used to measure the serum IgM1, IgG2 and IgM concentrations in pregnant an d non-pregnant ewes, rams and lambs over a period of eight months. The decrease of IgG1 and IgM concentrations which took place in ewes' serum at lambing was followed by a long and slow recovery phase (five to six months) during and after lactation, while no significant changes occurred in IgG2 concentrations. Serum immunoglobulin concentrations measured in a similar group of non-pregnant ewes throughout the same period showed no seasonal influence. Lambs' sera at three days after birth contained all three immunoglobulin classes and subclasses measured. There was no evidence of IgG2 deficiency. No sex differences were observed in immunoglobulin concentrations in lambs of all ages. Significant negative correlations were found between growth rate from six to 12 weeks and the IgG1 and IgG2 concentrations at 14 weeks.