Dietary Bovine Lactoferrin Increases Resistance of Juvenile Channel Catfish, Ictalurus punctatus, to Enteric Septicemia

Juvenile channel catfish, Ictalurus punctatus, were fed nutritionally complete, practical basal diets supplemented with bovine lactoferrin (Lf) at 0, 200, 400, 800, or 1600 mg/kg diet for 5 wk. Feed intake was significantly higher in fish-fed diets supplemented with Lf compared to the control diet, but the increased feed intake did not translate to significant increases in growth performance. Hemoglobin, white and red blood cell counts, and resistance to low-water stress also were not different among dietary groups (P > 0.05). Levels of Lf in diets had a significant effect on survival of channel catfish following challenge with Edwardsiella ictaluri: catfish fed 800 or 1600 mg/kg Lf had higher survival than the groups fed the control or 200 mg Lf diet. We established the break point minimum concentration of Lf for resistance to E. ictaluri infection as 1136 mg/kg. There was not a corresponding increase in activity of nonspecific or specific immune parameters with addition of Lf to diets, but plasma iron decreased significantly in channel catfish fed bovine Lf compared to the control group. However, no clear trend for level of dietary Lf, iron status, and resistance to E. ictaluri infection could be established. A number of chemical agents, polysaccharides, plant extracts, and some vitamins and minerals have been included in fish diets as immunostimulants to increase resistance to infectious disease by enhancing immune function (Sakai 1999; Raa 2000). Such immunostimulants are also being promoted in aquaculture as a means of overcoming the immunosuppressive effects of stress that commonly occur in intensive fish culture, even though few published reports support these claims. Much of the recent work on the effect of dietary supplementation of immunostimulants on fish health has focused on β-glucans and glucan subcomponents, but other immunostimulants, such as bovine lactoferrin, have also shown promise (Kakuta 2000). Lactoferrin (Lf), a bilobate iron-binding glycoprotein, is an antimicrobial component of milk and other exocrine secretions in mammals and is also released by activated 1 Corresponding author. neutrophils during the inflammatory process (Larkins 2005). Research indicates that Lf may have multiple roles in stimulating immune function in animals. The antimicrobial effects of Lf in mammals are in large part attributed to a strong capacity to bind iron, thereby reducing the availability of this essential element to bacteria (Dionysius et al. 1993; Ward and Conneely 2004), the action of the peptide lactoferricin formed from digestion of Lf (Gifford et al. 2005), and a direct killing effect by binding to the surface of bacteria (Arnold et al. 1982). Although research on dietary or oral administration of Lf has shown positive effects on immune function in humans and other warm-blooded animals, far less research has been conducted with aquatic species. However, lactoferrin is known to increase lysozyme activity, neutrophil respiratory burst (Kumari et al. 2003), production of macrophages, granulocytes, and neutrophils (Kakuta 2000), and phagocytosis and the killing response of phagocytic cells in fish (Sakai et al. 1993 and 1995; Kakuta 2000). Supplementation of Lf in the Published 2010. This article is a US Government work and is in the public domain in the USA.