Evaluating the Functional Properties of Spray-Dried Porcine Plasma in Gilthead Seabream (Sparus aurata) Fed Low Fish Meal Diets

SIMPLE SUMMARY: Spray-dried porcine plasma (SDPP) is considered one of the most promising functional ingredients as an alternative to the use of antibiotics, due to growth and immunity promotion. In the current work, we analyzed a mucosal immune response through challenging skin mucus antibacterial capacity and a systemic immune response through their splenocytes ex vivo with a pathogen-associated molecular pattern. Main skin mucus biomarkers were not modified by the SDPP diet, except for cortisol levels that were drastically reduced, which could be considered beneficial from a physiological perspective. In addition, the SDPP diet significantly reduced the growth of the pathogenic bacteria studied in the skin mucus. Anti- (tgf-β1), and pro-inflammatory (il-1β) cytokines, genes involved in humoral immunity (IgM), and the surface cell marker cd4 (cd4) were up-regulated in primary cell cultures of splenocytes exposed to lipopolysaccharide in fish fed the SDPP diet, which indicated that this functional ingredient was able to modulate the systemic immune response. In addition to promoting somatic growth, this study also indicated that SDPP, especially in the current low fish meal diets, seems to be useful and beneficial at the immunological level and mucosal health status, which makes it a good candidate for incorporation into the aquaculture sector. ABSTRACT: Blood by-products are an untapped source of high-quality ingredients for aquafeeds, containing a broad variety of cytokines, hormones, growth factors, proteins, bioactive peptides, and amino acids. The effects of the spray-dried porcine plasma (SDPP), a type of processed animal protein on several immune parameters, were evaluated in sea bream using ex vivo and in vitro assays. In this study, fish were fed with two isoproteic, isolipidic, and isoenergetic diets: control diet (7% fish meal, FM) and SDPP diet (2% FM and 5% SDPP). At the end of the 92-days trial, those fed the SDPP diet were larger in body weight (p < 0.05) without differences in feed conversion ratio (p > 0.05). The ex vivo immune stimulation of splenocytes indicated that SDPP had a beneficial effect in promoting systemic immunity, since the surface cell marker (cd4), pro- (il-1β), and anti-inflammatory (tgf-β1) cytokines, and genes involved in humoral immunity (IgM) were up-regulated. The co-culture assays of skin mucus corroborated that SDPP enhanced the antibacterial capacity of mucus against V. anguillarum. In addition, main mucus biomarkers did not show significant differences, except for cortisol levels which were lower in the SDPP diet. The present study indicated that SDPP may be considered a functional ingredient in aquafeeds formulated with low FM levels.