Protease improves performance, GHR gene expression, nutrient deposition, hematological, and biochemical indicators of Nile tilapia

Proteases are enzymes responsible for hydrolyzing proteins, which improves absorption. This study was conducted to determine the optimal level and assess the effects of protease in diets for Nile tilapia on performance, nutrient deposition, hematological and biochemical parameters, and the expression of genes associated with growth. An extruded control diet was formulated and supplemented with protease at four concentrations: 194, 316, 390, and 600 mg/kg (corresponding to 14,550, 23,700, 29,250, and 45,000 U/kg, respectively). Fish with an initial weight of 5.69 ± 0.27 g were fed these diets for 49 days. Nile tilapia fed the control diet showed lower performance compared to the 390 mg/kg diet. The optimal protease level recorded was 440 mg/kg. The crude lipid content was higher at the 600 mg/kg level but did not differ from the 390 mg/kg group. Protein and lipid retention were higher in the 390 mg/kg group than in the control group. The protease affected the body deposition of proteins and lipids. There was a positive linear effect on the number of red blood cells and a negative mean corpuscular volume. A lower concentration of amino acids was observed at higher levels of protease. In tissues (liver and muscle), the protease had a positive linear effect on the concentration of total proteins and amino acids and a negative impact on the ammonia content. In the liver, alanine aminotransferase activity showed a positive linear effect. The protease increased growth hormone receptor gene expression in the 390 mg/kg group. Exogenous protease has a positive impact on growth, feed efficiency, gene expression, and protein retention and deposition, without negative effects on hematological and physiological indicators of Nile tilapia. In conclusion, the estimated optimal inclusion level was 440 mg/kg of protease (33,000 U/kg).