Submitted to: Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/25/2006
Publication Date: 1/1/2007
Citation: Welker, T.L., Lim, C.E., Aksoy, M., Klesius, P.H. 2007. Growth, immune function, and disease and stress resistance of juvenile Nile tilapia (Oreochromis niloticus) fed graded levels of bovine lactoferrin. Aquaculture.262(2007):156-162. Interpretive Summary: Lactoferrin (Lf), a bilobate iron-binding glycoprotein, is an antimicrobial component of milk and other exocrine secretions in mammals. The antimicrobial effects of lactoferrin are attributed to stimulation of immune cells, a strong capacity to bind iron, thereby reducing the availability of this essential element to bacteria, and a direct killing effect by binding to the surface of bacteria. Lactoferrin has been added to diets of fish as a prophylactic treatment against disease, but results have varied depending on the species of fish and test conditions. Our objective was to determine the effects of graded levels of bovine Lf (0, 200, 400, 800, or 1600 mg/kg diet) on growth performance, hematology, immune function, and the resistance of Nile tilapia to Streptococcus iniae and stress. Dietary Lf did not affect growth performance or hematological parameters. Level of Lf in diet had a significant impact on mortality from S. iniae. Mortality was highest in control fish, declined significantly with increasing dietary level of Lf from 200 to 800 mg/kg, and increased slightly in the group fed 1600 mg/kg. Mortality from S. iniae did not appear to be related to the non-specific or specific immune response but may have been related to plasma iron or total iron binding capacity (TIBC), which decreased and increased, respectively, with increasing concentration of Lf in diet. Crowding stress produced significant increases on measured stress parameters from baseline values, but dietary Lf had limited impact on the stress response. The duration of most studies examining the effects of dietary Lf on fish health have been 30 days or less. Beneficial effects of Lf on some non-specific immune functions, and also the response to stress, may have occurred if the feeding duration were shorter.
Technical Abstract: Juvenile Nile tilapia (Oreochromis niloticus) were fed nutritionally complete, practical basal diets supplemented with bovine lactoferrin (Lf) at 0, 200, 400, 800, or 1600 mg/kg diet to apparent satiation twice daily for 8 weeks. After the feeding trial, the effect of dietary Lf on growth performance, immune function, and resistance to Streptococcus iniae challenge and low-water stress was determined. Dietary Lf did not affect growth performance (weight gain, feed intake, feed efficiency ratio, or survival) or hematological parameters (hemoglobin, white and red blood cell counts, or hematocrit) (P > 0.05). Level of Lf in diet had a significant impact on survival following S. iniae challenge (P < 0.05). Survival was lowest in control fish, increased with increasing dietary level of Lf from 200 to 800 mg/kg, and decreased slightly in the group fed 1600 mg Lf. Fish fed 800 mg/kg had significantly higher survival than control fish. There was not a corresponding increase in activity of non-specific or specific immune parameters (plasma lysozyme and spontaneous hemolytic complement activities or agglutination antibody titer against S. iniae) with addition of Lf to diets (P > 0.05), but plasma iron decreased and total iron binding capacity (TIBC) increased significantly with increasing concentration of Lf in diet (P < 0.05), which appeared to correspond with the increased survival to S. iniae infection. The ability of Lf to sequester iron, an essential nutrient required for the growth of bacteria, is regarded as one of its key antibacterial properties. Crowding stress produced significant increases in plasma cortisol, glucose, lactate, and osmolality from baseline values (P < 0.001). Dietary Lf did not significantly affect plasma glucose, osmolality, or cortisol concentrations (P > 0.05). The duration of most studies examining the effects of dietary Lf on fish health have been 30 days or less. Beneficial effects of Lf on some non-specific immune functions, and also the response to stress, may have occurred if the feeding duration was shorter.