Effect of mannan oligosaccharide and nucleotide supplementation on the zootechnical performance and differential and total hemocyte count of Penaeus vannamei subjected to ammonia resistance tests

Shrimp farming in Brazil has expanded rapidly due to strong domestic demand. However, the adoption of intensive production systems with high stocking densities increases shrimp susceptibility to environmental stressors, particularly the accumulation of nitrogenous compounds such as ammonia, which can negatively affect productivity. Feed additives, including mannan oligosaccharides (MOSs) and nucleotides (NTs), have been proposed as strategies to enhance the immune response of Penaeus vannamei under stressful conditions. This study evaluated the effects of dietary MOS and NT supplementation on the total hemocyte count (THC) and differential hemocyte count (DHC) of P. vannamei following an ammonia challenge. Shrimp (initial mean weight of 3.0 g) were fed for 60 days with one of four diets: Control (RC, without additives), RM (2 g MOS/kg), RN (2 g NT/kg), and NM (1 g MOS + 1 g NT/kg). After the feeding period, their performance parameters were analysed, and later the shrimp were exposed to ammonia stress for 96 h using an NH₄Cl stock solution for a final concentration of 0,5 mg/L of N-NH₃. The results showed that the animals fed with NM had the best FCR and the second best average final weight, whereas the MOS treatment showed the best survival rate. Increased THC was noted in shrimp fed RM and RN diets, whereas RC and NM treatments showed reduced hemocyte counts. DHC analysis indicated an improved immune response in shrimp receiving RN and NM diets, suggesting that MOSs and NTs, both individually and combined, contribute to mitigating the effects of ammonia-induced stress. These findings were further supported by survival rates. Nevertheless, the limited statistical differences among treatments indicated by the stress test show that the long-term recovery effects of these additives may be modest and warrant further investigation, although NM held the best performance before the stress test.