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Title: Effect of short-term feeding duration of diets containing commercial whole-cell yeast or yeast subcomponents on immune function and disease resistance in channel catfish, Ictalurus punctatus

Author
item Welker, Thomas
item Lim, Chhorn
item Aksoy, Mediha
item Klesius, Phillip

Submitted to: Journal of Animal Physiology and Animal Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2011
Publication Date: 3/1/2011
Citation: Welker, T.L., Lim, C.E., Aksoy, M., Klesius, P.H. 2011. Effect of short-term feeding duration of diets containing commercial whole-cell yeast or yeast subcomponents on immune function and disease resistance in channel catfish, Ictalurus punctatus. Journal of Animal Physiology and Animal Nutrition. doi:10.111/j.1439-0396.2011.01127.x.

Interpretive Summary: Research on dietary nucleotides in fish has shown that they may improve growth in early stages of development, enhance larval quality, and increase immune function and resistance to stress. Currently, there are numerous gaps in existing knowledge about supplementation of nucleotides in diets of fish and its effects on physiology and immunity. We examined the effects of dietary supplementation of purified nucleotides in diets of juvenile catfish on growth, immune function, and disease resistance. Nucleotide supplementation in channel catfish diets did not significantly influence growth performance during the 8 week study period. However, feed efficiency was considerably improved during the later portion of the study, suggesting that significant differences may have materialized if the study had been continued. The specific antibody response increased with increasing nucleotide concentration in diet, but the non-specific immune response was unaffected by dietary nucleotide supplementation. Addition of nucleotides to diet produced a reduction in survival of channel catfish to enteric septicemia (ESC). The high levels of nucleotides supplemented in this study may have contributed to the decrease in disease resistance and apparent contradiction with non-specific immune and specific antibody responses. Stress resistance increased with a corresponding decrease of the immunosuppressive effects of the stress response on non-specific immune function as nucleotides increased in diet. Based on the results of this study, supplementation of nucleotides in diets of channel catfish for prevention of ESC or as a growth promoter cannot be recommended, but use of exogenous nucleotides as a prophylactic treatment prior to culture-related stress exposure may prove beneficial by decreasing the immunosuppressive effects of stress.

Technical Abstract: Juvenile channel catfish (14.4 g average initial weight) were fed diets supplemented with a purified nucleotide mixture for 8 weeks. The mixture consisted of five nucleotides supplied on an equal basis as disodium salts at combined concentrations of 0 (control), 0.1, 0.3, 0.9, or 2.7% of diet. At the end of the feeding trial, the effects of nucleotide supplementation on growth, hematology, immune function, and resistance to enteric septicemia (ESC) and stress were evaluated. Nucleotide supplementation in channel catfish diets did not significantly influence growth performance at 8 weeks. However, feed efficiency from 4 to 8 weeks was considerably improved compared to the period from 0 to 4 weeks, suggesting that significant differences may have materialized if the study had been continued beyond 8 weeks. The specific antibody response increased with increasing nucleotide concentration in diet but declined at the highest level of supplementation. Innate immunity was unaffected by dietary nucleotide supplementation. Addition of nucleotides to diet produced a dose-dependent reduction in survival of channel catfish to E. ictaluri. Although the reasons are unclear, the high levels of nucleotides supplemented in this study may have contributed to the decrease in disease resistance and apparent contradiction with innate immune and specific antibody responses. Stress resistance increased with a corresponding amelioration of the immunosuppressive effects of the stress response on non-specific immunity (lysozyme and bactericidal activity) as nucleotides increased in diet. Based on the results of this study, supplementation of nucleotides in diets of channel catfish for prevention of ESC or as a growth promoter cannot be recommended, but use of exogenous nucleotides as a prophylactic treatment prior to culture-related stress exposure may prove beneficial by decreasing the immunosuppressive effects of stress.