Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 1/2/2006
Publication Date: 7/9/2006
Citation: Peterson, B.C., Bilodeau, A.L., Small, B.C. 2006. Effects of posilac on immune and endocrine responses of channel catfish challenged with edwardsiella ictaluri. American Society of Animal Science. Minneapolis, MN, July 9-13, 2006, p. 352. Interpretive Summary:
Technical Abstract: Research was conducted to examine the effects of recombinant bovine somatotropin (rbST, Posilac) on immune and endocrine responses to channel catfish challenged with Edwardsiella ictaluri. Four hundred and eighty fish (11.7 +/- 1.0 g) were randomly assigned to two treatments with six replicates each: 1) sham-exposed (one needle puncture per week for 3 wks and then challenged with and 2) rbST-exposed (Posilac, injected at 30 mg/g body weight per week for 3 wks and then challenged with E. ictaluri). Fish were sampled on d (1, 4, 8, or 14) (d 0 = E. ictaluri challenge). Non-exposed groups (d 0 controls) of fish were sampled on d 0. On each of the sample days, liver, kidney spleen, gut, and blood were collected. During the three-week period prior to challenge, rbST-treated fish gained 19% more (P < 0.01) weight. Levels of bacteria were higher (P < 0.05) on d 4 and 8 in rbST-exposed fish but were similar on d 14 compared to sham-exposed. Plasma levels of lysozyme were elevated (P < 0.01) in rbST-exposed fish on d 4, 8, and 14 compared to sham-exposed fish. Compared to d 0 controls, IGF-I levels decreased (P < 0.05) in challenged fish while levels were similar (P > 0.10) between treatments throughout the study. Similarly, abundance of GH receptor (GHR) mRNA tended to decrease (P = 0.06) in liver of challenged fish while levels were similar (P > 0.10) between treatments in the spleen, kidney, liver, and gut throughout the study. Abundance of toll like receptor 5 (TLR5) mRNA increased (P < 0.05) in liver of fish challenged with bacteria compared to d 0 controls while levels were similar (P > 0.10) between treatments in the spleen, kidney, liver, and gut throughout the study. Mortality was higher in rbST-exposed fish compared to sham-exposed fish. An increase in lysozyme in rbST-exposed fish may reflect increases in bacterial levels of E. ictaluri. A decrease in GHR mRNA and plasma IGF-I suggests a down regulation of the somatotropic axis in response to disease. While TLR5 mRNA increased in response to disease, there was no apparent effect of exogenous rbST.