Effects of Dietary Yeast Nucleic Acids and Free Nucleotides on Growth Performance, Digestive Enzyme Activities, Immune Parameters, Tolerant to Hypoxic Stress and Disease Resistance in Juvenile Pacific White Shrimp ( Litopenaeus vannamei )

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Abstract
Yeast nucleic acids and free nucleotides (yeast RNA + NT) is a functional feed additive with health‐promoting effect. This study aimed to evaluate the effect of dietary yeast RNA + NT (from Kluyveromyces fragilis ) on the health conditions, hypoxic stress tolerance and disease resistance in juvenile Pacific white shrimp ( Litopenaeus vannamei ). Shrimp were fed diets supplemented with 0, 0.25, 0.50 and 0.75 g·kg −1 yeast RNA + NT for 45 days, followed by challenges with hypoxic stress and Vibrio parahaemolyticus (AHPND). Results showed that yeast RNA + NT supplementation at 0.50 g·kg feed −1 could significantly improve body weight (3.93 g), FCR (1.20), trypsin activity (78.02 mU·mg protein −1 ) and trypsin‐to‐chymotrypsin ratio (5.03) compared to the control (3.34 g, 1.59, 64.70 mU·mg protein −1 and 3.78, respectively). All three yeast RNA + NT groups had significantly higher survival rates and lower Vibrio spp. counts in the hepatopancreas. The highest immune responses were observed in the yeast RNA + NT at 0.75 g·kg feed −1 group. Survival rates under hypoxia were significantly higher in the yeast RNA + NT at 0.50 (81.67%) and 0.75 g·kg feed −1 (80.00%) compared to the control (45.00%). Notably, the 0.75 g·kg −1 group exhibited the highest resistance to AHPND, with a survival rate of 65.00% compared to 43.33% in the control. These findings suggest that 0.50 g·kg −1 is optimal for growth promotion, whereas 0.75 g·kg −1 maximises immune function and resistance to hypoxia and bacterial infection.
Funding Information
  • Regione Lombardia
  • European Regional Development Fund

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