By P. W. Cardozo
Carotenoid Technologies, IQF Group, Pol. Industrial Francoli, 43080 Tarragona, Spain.
INTRODUCTION
Nutrient digestibility improvement using feed additives, such as antibiotics, has proved to be a useful strategy to improve production efficiency in animal nutrition. However, the use of antibiotics as feed additives in animal feeds was banned in European Union since 2006 due to the potential of appearance of residues in end products (Russell and Houlihan, 2003) and multiresistant of strains. Since then, considerable time, effort and expense have been invested in the development and evaluation of alternative products, including acidifiers, enzymes, prebiotics, probiotics and plant extracts leading to the universal conclusion that an effective strategy lies not on one, but most often on a combination of products.
Natural antimicrobials such as plant extracts, generally recognized as safe for human consumption (FDA, 2004) have been used for centuries for various purposes (as traditional medicine and food preservatives, among others) due to their antimicrobial properties (Davidson and Naidu, 2000). The antimicrobial activity of plant extracts is attributed to a number of secondary plant metabolites, from which terpenoids (such as carvacrol, thymol) and phenylpropanoids (like cinnamaldehyde, eugenol, or anethol) present in the essential oil fraction of many plants can exert multiple effects on the organism including improvement of feeding efficiency and digestion, reduction of ammonia, and improvement of gut flora and health status.
NEXT Enhance®150 is characterized by a standardised 1:1 combination of thymol and carvacrol in a unique protection capsule which protects the active substances under pelleting and expanding conditions and releases the active components to the lower intestinal tract where they are most needed by the animal. There is a number of in vivo studies in different livestock species showing the benefits of NEXT Enhance® 150 on improving gut flora equilibrium, enhancing nutrient assimilation and reducing pathogen stress, especially in the young animal.
The aim of this study was to evaluate the effects of the supplementation of NEXT Enhance® 150 in shrimp diets on production parameters and survivability of white shrimps (Litopenaeus vannamei), especially fingerlings, grown under normal and stress conditions from Vibrio harveyi, being infected artificially at 1 and 28 days.
MATERIAL AND METHODS
Trial site and experimental design
The present study was performed by the Agricultural Department, School of Fisheries at Kasetsart University, Bangkok, Thailand.
White shrimp (Litopenaeus vannamei) stocks were selected with an average liveweight of 5 g and were allocated randomly to glass aquarium tanks (45 cm wide, 60 cm long and a water level of 30 cm deep). Shrimp were stocked at a density 40 shrimp/m2 in 15 ppt seawater. Temperature was established at 28.0 ± 1.0ºC, with dissolved oxygen at 6.5 mg/litre and all groups were fed under the same conditions (at 2-2.5% body weight) at 3 times daily. The seawater was changed twice weekly.
The study was conducted during 56 days in a completely randomized block design with 4 treatments and 12 replicates each, Shrimps from 6 replicates were grown under normal commercial conditions, and the other 6 replicates were challenged by bath treatment with virulent Vibrio haveyii for 10 days at 1 and 28 days of experiment, respectively.
White shrimp (Penaeus vannamei )
Trial treatments
The treatments were assigned as follows:
Group 1: Commercial shrimp feed without additive (Control)
Group 2: Commercial shrimp feed + NEXT Enhance® 150 at 30 ppm
Group 3: Commercial shrimp feed + NEXT Enhance® 150 at 60 ppm
Group 4: Commercial shrimp feed + Antibiotic Enrofloxacin at 10 ppm
Measured parameters
1. Performance parameters on replicated under normal conditions
Growth performance, body weight, daily weight gain, feed intake, feed conversion ratio (FCR), and survival rate were measured at 28 and 56 days, respectively.
2. Immune status and disease challenge
Shrimps of 3 replicates for each treatment were used at the first month, and shrimps for other 3 replicates of each were used also for second month to evaluate the immunological parameters such phagocytic activity, and Prophenoloxidase activity (ProPox) as a consequences to artificial infection with Vibrio harveyi at day 1, and 28, respectively.
Shrimp culture and disease challenge condition
Statistic analyses
The effects of the supplementation of NEXT Enhance® 150 in shrimp diets on production parameters and survivability of white shrimp (Litopenaeus vannamei) under stress conditions from Vibrio harveyi were tested using the PROC MIXED procedure of SAS (version 8.12; SAS Institute, Cary, NC) for completely randomized block design. The Duncan’s Multiple Range Test was used to determine the differences between the treatment means. Differences were declared at P < 0.05.
RESULTS
Growth performance
The shrimp performance results of all treatment in two periods are presented in Table 1. In general, there were numerical differences were observed during the 28 days, especially for NE 150 at 30 and 60 ppm, which increased liveweight, and average daily gain (ADG), reducing FCR compared with control.
Table 1 Effect on various performance parameters of white shrimps fed a commercial feed alone, or with NEXT Enhance® 150 (NE 150) at 30 or 60 ppm, or with Enrofloxacin at 10 ppm
On day 28 to 56, final liveweight, daily weight gain and feed conversion were all improved (P < 0,05) with the diet supplemented with NEXT Enhance® 150. In addition, the effects of many parameters improved over time. Taking in account the overall parameters from 1 to 56 days, NE 150 at 30 ppm improved (P < 0.05) the ADG, and FCR compared with control. In addition, NE 150 at 60 ppm also improved (P < 0.05) FCR compared with control and Enrofloxacin group.
White shrimp fed the NEXT Enhance® 150 at 30 and 60 ppm in diet, respectively, improved by 15% survival rate compared to control, and improved by 4% compared to the antibiotic Enrofloxacin group.
The percentage of glycogen accumulation in hepato-pancreas was also higher (P< 0,05) in the NEXT Enhance® 150 groups than in the other treatments (Table 1). These results are correlated with a higher growth rate and molting cycle. In general, glycogen represents stored energy that the organism can use as energy during the molting period (Abdel-Rahman, 1979; Omondi and Stark, 1996; Rosas, et al., 1995; Sanchez A., 1991; van Handel, 1965; Shiau, 1992).
Hemocytic activity
The immune status in white shrimp is presented in Table 2. Shrimps fed NEXT Enhance® 150 at 30-60 ppm showed a higher hemocytic activity (p<0.05) in term of phagocytosis activity than the other groups, meaning that when the shrimps were infected by pathogens, the hemocyte cell moved to engulf the pathogen very quickly and released phenol to destroy pathogen cell. NEXT Enhance® 150 at 30-60 ppm can increase the hemocytic activity because of the high anti-oxidant properties of its active ingredients thymol and carvacrol which can enhance the healthy hematocyte activity and protect hematocyte cell damage.
Table 2 Effect on hemolymph parameters of white shrimps fed a commercial feed alone, with NEXT Enhance® 150 (NE 150) at 30 or 60 ppm, or with Enrofloxacin at 10 ppm
Disease challenge of Vibrio harveii
The four treatment groups were challenged by bath treatment with virulent Vibrio harveyi for 10 days. Mortality rate was determined through the whole period of the trial. The results are shown in Table 3. Shrimps fed Enrofloxacin at 10 ppm and NEXT Enhance® 150 at 60 ppm showed a better (p<0.05) disease resistance. In both groups, the number of Vibrio harveyi which infected hepato-pancreas was lower (p<0.05) than the other groups. Enrofloxacin has been previously shown to directly inhibit pathogenic growth (Alderman, 1988, Valle, 1999). However, there is evidence of bacterial resistances (Gómez, 1998). In the case of plant extracts and their active ingredients (NEXT Enhance® Groups), there is no evidence of thymol and carvacrol on bacterial control in white shrimp. However, the results from this study seem to show that the use of NEXT Enhance® 150 helps to control pathogenic gut flora growth as well as immune system actions. This would enable the product to act without the concern of bacterial resistances.
Table 3 Effects on survival rate of white shrimp challenged by Vibrio harveyi fed a commercial feed alone, with NEXT Enhance® 150 (NE150) at 30 or 60 ppm, or Enrofloxacin at 10 ppm.
CONCLUSION
The results from the present study showed that the supplementation of white shrimp diets with NEXT Enhance® 150 during the growth period improved feed utilisation leading to significant benefits on daily weight gain. The significant benefits on carbohydrate utilisation as indicated by higher glycogen deposition in the hepato-pancreas should provide a source of additional energy for optimal growth.
Regarding the immune response, the results obtained showed that the supplementation with NEXT Enhance® 150 improved phagocytic activity, prophenyloxidase activity, and reduced the number of colonies of Vibrio harveyi which leads to a lower level of mortality. Furthermore, NEXT Enhance® 150 showed results comparable to classical in-feed antibitiotics, without the possibility of residues or resistances.
The action of NEXT Enhance® 150 and its role on the immunity of crustaceans, is of great commercial interest as it opens the possibility to design sustainable measures to improve aquaculture productivity, especially under pathogen challenge.
We can conclude that the routine supplementation of NEXT Enhance® 150 at 30 ppm during one or two months is recommended for normal growth conditions, and adding NEXT Enhance® 150 at 60 ppm is recommended for growth and survival in stress conditions.
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