In-feed Arthrospira (Spirulina) platensis supplementation enhances breast yield in heat-stressed broilers through...

Heat stress (HS) is a significant economic, welfare, and production burden to worldwide poultry production sustainability. Therefore, effective and sustainable mitigating strategies are needed. Driven by consumer's changing preferences and demand for natural products, microalgae have attracted substantial attention from the poultry industry and have become the fastest growing segment of animal feed additives, yet their modes of action are still not well defined. This study aimed to determine the effect of Arthrospira platensis (Spirulina, SP) on growth performance in heat-stressed broilers and to delineate its underlying mechanisms by using in vivo and in vitro studies. Six hundred one-day old male Cobb500 chicks were randomly allocated to 12 environmental chambers (2 floor pens/chamber, 24 pens in total, 25 birds/pen) and fed two diets (standard control diet, C vs. SP-supplemented diet at 0.5% inclusion rate). On day 29, birds were exposed for two weeks to 2 environmental conditions (thermoneutral, TN, 24°C vs. cyclic HS 36°C, 8h/day). Growth performances, carcass parameters, and muscle myopathy incidences were determined. Chicken primary embryonic myoblasts (CPEM) were isolated, cultured, and treated with either benzoic acid (BA) or quercetin (QCT)-compounds abundant in SP- prior to a 6-h exposure to HS (45°C) or control conditions (37°C). Gene and protein expressions involved in protein proteostasis network (synthesis, degradation, and chaperonin) were measured by qPCR, immunoblot, and immunofluorescence. Data were analyzed by two-way ANOVA and Tukey test, and significance was set at P < 0.05. Heat stress significantly increased core body temperature (CBT) and water intake and depressed feed intake and growth performance in broilers. In-feed SP supplementation reduced CBT, improved water conversion ratio (WCR) by 36.5 points, and enhanced breast yield, without affecting muscle (woody breast and white striping) myopathies. Supplementation of SP significantly increased the phosphorylated levels of mTOR^Ser2481, mTOR^Ser2448, and S6K^{Thr421/Ser424}, decreased p-eIF2α^Ser51, ubiquitin, and HSP60/90 in heat-stressed broilers. Treatments of CPEM with BA or QCT recapitulated the effects of SP. Collectively, supplementation of SP enhanced breast yield in heat-stressed broilers through modulation of proteostasis network by enhancing protein synthesis (mTOR-S6K-eIF2α pathway), reducing protein degradation (ubiquitin machinery), and regulating chaperonins.