The arginine sparing benefits of guanidinoacetic acid (GAA) as the precursor of creatine in broilers fed reduced protein (RP) diets has been documented (Sharma et al., 2022). However, the effectiveness of GAA in RP diets on performance and gut health of broilers under heat stress is largely unknown. A 35-d experiment was conducted using four dietary treatments: a standard protein diet (SP, 221 and 207 g/kg CP in grower and finisher), a RP diet (201 and 187g/kg in grower and finisher), a RP diet with 0.92 g GAA per kg diet substituting 50% of supplemented arginine (GAA50) at one to one ratio and a RP diet with the same amount of GAA added on top (GAAtop). From d 0 to 10, all birds received the same diet as per Ross 308 requirements. Day-old male chicks were assigned to 64 pens (10 birds each) in two rooms. In each room, each diet was replicated 8 times. From d 25 to 35, birds in one room were subjected to a cyclic heat stress (32±1 ⸰ C for 8 hours). To assess intestinal permeability (InP), on d 27, an oral gavage of fluorescein isothiocyanate-dextran was used (4.16 mg/kg BW). There was no interaction between diets and heat stress for any of the performance parameters (Table 1). Body weight gain (BWG) was unaffected by dietary treatments. From d 10 to 24, feed intake and FCR were not affected. GAA50 followed by GAAtop significantly decreased the feed intake during the finisher phase (P<0.01) and from d 10 to 35 (P<0.001), compared with SP diet. At the same time, birds fed SP diet had the highest feed consumption. Heat stress reduced (P<0.0001) feed intake and BWG at any stage of the study but did not impact FCR. The GAA50 tended to reduce FCR from d 24 to 35 (P=0.086) and d 10 to 35 (P=0.082) compared with SP and RP. Heat stress increased (P<0.05) InP whereas diets had no effect. The results indicate that replacing 50% of supplemented arginine with GAA tends to improve FCR by reducing the feed intake under both thermoneutral and heat stress conditions. Additional analysis is underway to investigate association between GAA and gut health
considering the involvement of creatine in energy balance of enterocyte and indirect effects on gut integrity.