White feces syndrome (WFS) is considered a major cause of significant crop failures of white shrimp in Asia. Multiple pathogenic combinations have been associated to the disease, including Vibrio spp. bacteria, parasitic protozoa known as gregarines, and microsporidian parasites such as Enterocytozoon hepatopenai (EHP). Preventive approaches rather than curative are the most efficient control strategies against the disease, one of them being the dietary inclusion of functional feed additives that deliver antimicrobial and antiparasitic activities to the digestive system and boost the immune system. The present research evaluated the efficacy of a phytobiotic-based feed additive against WFS causative pathogens under laboratory and field conditions.
A first laboratory trial to evaluate the efficacy of the functional feed additive against Vibrio spp. bacteria was conducted at ShrimpVet (Vietnam). Shrimp (~1 g) were fed with control and additive treated (3 kg/ton) feeds during 14 days pre-infection. Infection was performed via feed coated with Vibrio culture (WFD5) and first signs of disease were detected after 24 hours. Dietary inclusion of the functional feed additive significantly reduced disease prevalence and mortality during 14 days post-challenge by 54% and 33%.
A second laboratory trial to evaluate the inhibitory efficacy of the functional feed additive against EHP germination was conducted at Biotec (Thailand). EHP spores were purified from hepatopancreas of two different batches of infected shrimp and incubated during 120 min with the additive at 3 and 6 g/L (i.e. equivalent to the dietary inclusion of the additive at 3 and 6 kg/ton). Germination rate of EHP spores averaged 70% in control groups, while the feed additive at both concentrations completely inhibited germination.
Laboratory results were further validated under field conditions in two trials executed in collaboration with shrimp producers. The general trend observed was that a preventive dose (2-3 kg/ton) of the additive can recover average daily growth to acceptable levels after elimination of signs of disease and result in higher biomass.
Altogether, laboratory and field data prove the efficacy of phytobiotic-based feed additive as preventive strategy to reduce the likelihood and severity of WFS outbreaks and to ensure growth recovery post-outbreak.