PhD in Veterinary Sciences for Animal Health and Food Safety

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Supervisor

Phd thesis

Abstract

Gut health is defined as the absence/avoidance/prevention of gastrointestinal diseases in order to maintain animal welfare, health and performances. In poultry farming, the maintenance of an appropriate gut health has become a major issue since 2006, when the European Union bans the use of antimicrobial growth promoters in animal feed. The aim of this PhD project was to assess whether insect live larvae (Hermetia illucens -HI and Tenebrio molitor-TM) or functional feed (Alphasoy Gold-ASG) can have beneficial effects on gut health of poultry using a multidisciplinary approach including histopathological, histochemical and biomolecular techniques. For this purpose, three experimental trials were performed. In Trial 1 and 2, a total of 180 chickens and 126 Muscovy ducks were randomly allotted to three dietary treatments: Control, HI and TM. In both trials all the animals were fed a commercial diet and HI and TM groups received 5% of the expected daily feed intake of HI and TM larvae, respectively. In trial 3, a total of 576 as-hatched male broiler chickens were randomly allotted to 3 dietary treatments to explore the effects of ASG obtained by thermomechanical co-processing of soybean meal and hydrolyzed yeast (b-glucan) on gut health during pre-starter and starter phase: T1 (20% and 10% of ASG), T2 (5% of ASG in both phases) and a control group. At slaughter, samples of duodenum, jejunum, ileum, spleen, liver, thymus and bursa of Fabricius were collected for histomorphometric analysis. Mucin composition was evaluated in the small intestine through histochemistry while MUC-2, selected cytokine and tight junction expression was evaluated by rt-qPCR. Cecal microbiota was also analyzed (Trial 1 and 2). Considering trial 1 and 2, HI and TM did not impair intestinal morphometry, mucin composition and MUC-2 transcription levels (P>0.05), maintaining the integrity of the mucosal barrier. On the contrary, TM group showed lower pro-inflammatory cytokine IL-2 (P= 0.044, Trial 1) and higher anti-inflammatory cytokine IL-6 transcription levels (P=0.009, Trial 2), suggesting that the lower chitin content recorded in TM can positively modulate the local immune response towards an “anti-inflammatory pattern”. In caeca, HI and TM slightly increased short-chain fatty acids producing bacteria, which provide an important energy source for the enterocytes. Regarding trial 3, ASG did not impair the intestinal barrier function, maintaining the proximo-distal decreasing gradient of the morphometrical indices and the integrity of the tight junctions at day 3 and 10 (P>0.05). Moreover, MUC-2 expression was reduced in T1 group at day 3, suggested that ASG can reduce the intestinal inflammation and the need of mucous synthesis from goblet cells. This is further confirmed by the reduction of pro-inflammatory cytokines (IL-2, TNF-a and INF-g) in the duodenum of T1 and T2 chicks at day 3.In all the three trials, insect live larvae and ASG did not influence the severity of the observed histopathological lesions, thus suggesting that they did not negatively affect animal’s health.

In conclusion, the present PhD project provides new insights about the use of insect live larvae and functional feed in poultry nutrition. The results herein obtained suggests that both chitin and b-glucans can act as probiotic/prebiotic in poultry farming, showing positive effects on gut health immune response and gut microbiota, without impairing gut morphometry, mucin and tight junctions.

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