Serum Immunoglobulin Profiles of Dairy Cows Chronically Treated with Recombinant Bovine Somatotropin

¹ Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada N1G 2W1

The objective of this study was to determine the effects of exogenous somatotropin on blood profiles of the major bovine Ig isotypes. Holsteins were treated with either 0, 10.3, or 20.6 mg recombinant bST/d. Subcutaneous injections were started between wk 4 and 5 of lactation and continued for 266 d. Blood samples were collected by coccygeal venipuncture throughout lactation for serum IgG, G₁, G₂, A, and M concentration determination. Cows treated with 10.3 mg of bST/d exhibited modest increases in mean blood concentrations of IgG (12.4%) and IgG₂ (18.4%) relative to the other groups of cows. In addition, treated cows had 10.1% higher average concentration of IgA than controls. Somatotropin did not influence average lactational concentrations of IgG₁ or IgM, although the group receiving 10.3 mg/d had higher late lactation concentrations of IgG₁ than did the other two groups. However, treatment mean isotype concentrations were always within normal ranges, except for IgG₂ from the 10.3 mg/d group, which were higher. The practical significance of elevated serum Ig concentrations observed in the present study is not known. However, the present data do show that bST administered at doses that increased milk yield had no apparent detrimental effect on humoral immunity as measured by blood concentrations of Ig.

Key Words: somatotropin • immunoglobulins

Submitted on August 6, 1990
Accepted on December 10, 1990