Evaluation of dried porcine solubles in diets of Rice field eel (Monopterus albus)

Abstract

Porcine solubles, originating from porcine mucosal tissues, is a by-product of heparin production. The nutritional value and functionality of a carrier-free, spray-dried porcine soluble (DPS) product was evaluated in 56-day experiment with juvenile rice field eel Monopterus albus (initial weight: 15.5 ± 0.19 g) fed diets with optimal (42%) and a low level (22%) of fishmeal (FM) inclusion. Six isonitrogenous and isolipidic experimental diets were formulated with two levels of FM (22% and 42%) and three levels of DPS (0%, 2.5% and 5%). Growth performance, humoral immunity, digestive enzyme activities, intestinal histology and expression of intestinal tight junction protein-related mRNA were analyzed at the end of the trial. Similar to FM, inclusion of 5% DPS significantly enhanced growth rate and reduced feed conversion ratio of rice field eel, although no significant interaction between FM and DPS on growth performance were observed. Positive influences of DPS on fish health and immunity were seen in that inclusion of DPS significantly enhanced serum complement (C3, C4), immunoglobulin M (IgM) levels and lysozyme activities, and altered total cholesterol and triglyeride contents in the serum of rice field eel. In regard to gut health, villus height, goblet cell quantity and expression of ZO-1 transcripts significantly (P < 0.05) increased with DPS inclusion in fish fed low-FM diets but was not observed in fish fed diets containing the optimal level of fishmeal. Expression of ZO-2 and CL-12 transcripts in intestine also was significantly (P < 0.05) elevated by DPS inclusion in fish fed diets containing low or optimal FM. Moreover, FM and DPS showed significant (P < 0.05) interactions in the expression of inflammatory cytokines mRNA in the intestine of rice field eel with 5% DPS inclusion significantly (P < 0.05) promoting the expression of Tgfb2 and IκBe mRNA, while repressing IL-1β, IL-8, IL-12 and IFNγ expression in fish fed diets containing low FM. This study is the first to show functionality of DPS supplementation at 5% of diet in any aquatic species. Based on these results, DPS supplementation should be considered as an effective, innovative and sustainable strategy to improve health, as well as reduce intestinal inflammation and maintain normal intestine structure of rice field eel fed low-FM diets.