Anti-idiotypic responses of lactating cows immunized with monoclonal antibodies against bovine somatotropin

The objective of this study was to produce antiidiotypic antibodies with bo vine somatotropin (bST)like activity by active immunization of lactating co ws and to determine their effects on milk yield. Several monoclonal antibod ies against bST were evaluated for their interaction with bST in a rat grow th bioassay. Two bST-agonist monoclonal antibodies (1 and 2), and two bST-a ntagonist monoclonal antibodies (3 and 4) were selected. Cows were immunize d with immunoglobulin G as a control (n = 12) or with one of the four anti- bST monoclonal antibodies (1, 2, 3, 4; n = 12) on d 3, 24, 45, 665 87, 108, 129, and 150 of lactation. From wk 3 of lactation, all cows immunized with each of the four anti-bST monoclonal antibodies developed anti-idiotypes u ntil wk 30 of lactation. Total lactation yields were not different among mo noclonal antibodies 2, 3, and 4 and control cows (9299, 9321, 9733, and 941 5 kg; respectively). However, cows immunized with anti-bST monoclonal antib ody 1 had reduced lactation yield compared with cows on other treatments (8 136 kg). Daily milk yield of cows immunized with monoclonal antibody 1 was decreased from wk 9 of lactation [36.2 vs. 40.9 kg/d (control)] until the e nd of lactation, concomitantly with decreased bST concentration from wk 9 o f lactation; Cows immunized with anti-bST monoclonal antibody 4 had increas ed milk yield compared with that of controls during wk 3 to 6 and wk 18 to 21 of lactation. Therefore, anti-idiotypes directed against anti-bST 1 had bST-antagonistic effects on lactation performance; anti-idiotypes against a nti-bST 4 transiently increased milk yield.