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Title: ASSESSMENT OF RECOMBINANT BOVINE SOMATOTROPINTM (RBST) AS AN IMMUNOMODULATOR DURING AVIAN COCCIDIOSIS: IMMUNIZATION WITH LIVING OOCYSTS

Author
item Allen, Patricia
item Danforth, Harry
item GREGORY, SUSAN - MONSANTO CO, ST.LOUIS, MO
item COMENS-KELLER, PATRICIA - G.D. SEARLE, ST.LOUIS, MO

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Coccidiosis costs the American poultry industry approximately $350 million a year. Control has been primarily through the prophylactic use of anticoccidial drugs. However, because many coccidia species have developed strains resistant to a large number of these drugs, alternate means of control, particularly use of vaccines, are being sought. As part of this effort we have tested recombinant bovine somatotropin (rbST) for its ability to stimulate protective immunity to coccidia infections, in order to determine its possible usefulness as an immune modulator or adjuvant in vaccination regimens. Using lesion scores as an indicator, we found that two subcutaneous injections alone of 0.09 mg/chick reduced cecal lesion scores when chickens were challenged with E. tenella. One injection, in conjunction with treatment with the live oocyst vaccine, IMMUCOX, was also protective against E. tenella, compared to treatment with the vaccine alone. Under the experimental conditions, rbST did not improve immunity against E. acervulina or E. maxima developed by live oocyst administration. Nevertheless, since rbST was protective against E. tenella, the least immunogenic Eimeria species, the results suggest that this compound can act as an immunomodulator during coccidiosis, and provide a basis for further investigations of its use as a vaccine adjuvant.

Technical Abstract: Coccidiosis, a disease of great economic importance to the poultry industry, is generally controlled prophylactically by additions of anticoccidial drugs to the feed. However, increasing development of drug resistant coccidia species has stimulated searches for alternative control methods, one of which is vaccination. As part of this effort, recombinant bovine growth hormone (rbST) was tested as a possible immune stimulator in combination with live oocyst vaccination. At a dose of 0.045 mg/chick, given by subcutaneous (SC) injection at 1 day of age, rbST did not improve immunity developed by immunization with 500 or 2500 oocysts of E. maxima as judged by weight gain and lesion scores. At a single dose of 0.09 mg/chick given at 1 day of age in combination with IMMUCOX rbST provided some protection against challenge infection with E. tenella but not E. acervulina as judged by reduction in lesion scores. Treatment with .09 mg rbST/chick alone at 1 and 3 days of age was protective against challenge with E. tenella but not E. acervulina or E. maxima as judged by reduction in lesion scores. These results strongly indicate that rbST can act as an immune modulator in chickens infected with coccidia, particularly E. tenella, and provide a basis for further investigations of its use as a vaccine adjuvant.