Effect of dietary butyric acid, Bacillus licheniformis ‎ (probiotic), and their combination on hemato-biochemical indices, antioxidant enzymes, immunological parameters, and growth performance of Rainbow trout (Oncorhynchus mykiss)

Abstract

This study was performed to investigate the effects of dietary butyric acid, probiotic (Bacillus licheniformis‎), and their combination on hematology and biochemical indices, liver antioxidant enzymes, immune parameters, and growth performance of rainbow trout (Oncorhynchus mykiss). Three hundred healthy rainbow trout fish (average initial weight = 13.33 ± 0.20 g) were fed four isonitrogenous (40.99 g kg-1 crude protein) diets. The first diet (D1) was control. The other three diets D2, D3and D4 were supplemented with 2.2. × 107 CFU g-1B.licheniformis, 2 % butyric acid and 2 % butyric acid + 2.2. × 107 CFU g-1B.licheniformis diet, respectively. The results indicated that fish receiving diets 3 and 4 have the highest hematology parameters, total protein, albumin, and globulin. No significant difference (P > 0.05) was observed in the serum level of alanine aminotransferase (ALT), alkaline ‎phosphatase (ALP), ‎ and liver superoxide dismutase (SOD) activity among experimental diet groups. The liver catalase (CAT) and glutathione peroxidase (GPX)‎ activity were significantly in fish fed with diets 2, 3, and 4 (P < 0.05). The most improvement in total immunoglobulin (Ig) concentration, lysozyme, and serum bactericidal activity were observed in fish fed with diets 3 and 4 (P < 0.05). The challenge test showed that the order of resistance to S. agalactiae infection was in fish fed with diets 3, 4, and ‎2, respectively. The fish fed with diet 4 exhibited the lowest feed conversion ratio and the highest final body weight, weight gain, and specific growth rate (P < 0.05). In general, this study showed that dietary administration of butyric acid alone or ‎combined with B. licheniformis provides promising results as a functional feed for the ‎rearing of rainbow trout.‎