ผลของการเสริมเอนไซม์โปรติเอสในอาหารกุ้งขาวต่อการเจริญเติบโต สัมประสิทธิ์การย่อยอาหาร และความต้านทานโรค

Abstract

This study investigated the effects of exogenous protease enzyme supplementation on Pacific white shrimp, Litopenaeus vannamei as a result of replacing fish meal with plant protein from soybean meal in comparison with a high fish meal diet, on growth performance, feed utilization, enzyme activity, immunity and disease resistance. Shrimp with an initial average body weight of 2.33g, were randomly sampled and reared in 220-liter rectangular plastic tanks at the stocking rate of 30 shrimp per tank with 15 ppt seawater. Shrimp were fed experimental diets four times daily for 8 weeks. Feeding trial was operated by 3×2 factorial experimental design, composed of 6 treatments with 5 replications each. Two factors were examined. First of which had 3 different levels of fish meal including 180g kg (PC), 100g kg-1 (NCI) and Og kg-1 (NC2). Each fish meal level was divided into two groups, i.e. un-supplemented and supplemented with 175mg kg exogenous protease enzyme. All diets were formulated to reach iso-proteic (38%) and iso-energetic (19kJ g). In low fish meal diets (NC1 and NC2), fish meal (from PC diet) was replaced by soybean meal. The results exhibited no significant differences in growth performance between shrimp fed PC diet and NC1 diet (P > 0.05), whereas digestive enzyme activity, i.e. protease, amylase and cellulase as well as apparent digestibility coefficients (dry matter and crude protein) of NC1, significantly decreased (P < 0.05). However, growth performance, feed intake and digestive enzyme chymotrypsin and cellulase activity, as well as apparent digestibility coefficient of crude protein were significantly lower for NC2 compared to the PC and NC1 (P<0.05). Moreover, there were no differences in survival rate, feed utilization and all immune parameters including total hemocyte count, hemolymph oxyhemocyanin content, the ratio of oxyhemocyanin to hemolymph protein, phenoloxidase activity, catalase activity, malondialdehyde content and cumulative mortality after challenge with V. harveyi for 14 days among treatment groups (PC, NC1 and NC2) (P>0.05). Exogenous protease supplementation in low fish meal diets had a positive influence on feed utilization as the result of an improvement in feed conversion ratio and an enhancement of protein efficiency ratio, apparent net protein utilization, digestive enzyme activity including trypsin, chymotrypsin, lipase and cellulase, as well as apparent digestibility coefficients of dry matter, crude protein and gross energy (P < 0.05). Furthermore, there was significant attenuation of oxyhemocyanin content and the ratio of oxyhemocyanin to hemolymph protein which might be due to the decreased energy demand for digestive activity and shrimp response against antigenic proteins from soybean meal. However, supplementation of the protease showed no significant differences in growth performance, survival rate, other immune parameters and cumulative mortality during disease challenge test (P > 0.05). Our results indicated that the reduction of fish meal levels up to 45% in shrimp diet when a low fish meal diet was replaced with soybean meal and supplementation of protease at 175mg kg-1 in the diets could improve the feed utilization and apparent digestibility coefficients of Pacific white shrimp.