EFFECT OF A MULTI-STRAINS YEAST-BASED FUNCTIONAL ADDITIVE ON EHP-CHALLENGED JUVENILE WHITE SHRIMP Litopenaeus vannamei

Enterocytozoon hepatopenaei (EHP) is an intracellular parasite targeting the shrimp hepatopancreas (HP) and gut epithelial lining causing stunt growth. It generates severe losses across Asia either directly or in association with other pathogens. Lallemand Animal Nutrition has developed a multi-strains yeast-based additive (YANG) presenting contrasted microbe-associated molecular patterns for broad immune-modulation at low inclusion level.

The trial lasted 34-day (14-day pre-challenge, 10-day EHP challenge by cohabitation; 10-day post challenge period) using juvenile whiteleg shrimp (BW = 0.61 ± 0.01 g) stocked within 120L self-contained test units allocated to 3 treatments (9 replicate units/ treatment; 30 shrimp / unit): A negative control (basal diet; non-challenged); a positive control (basal diet; EHP-challenged) and a supplemented diet (YANG at 800 g/T; EHP-challenged). The EHP-load in the HP was measured by qPCR at day 0, 5 and 10 post-challenge (GLM; post-hoc Wald test).  

Survival averaged 81 ± 2 % across groups with no significant differences between the negative and positive controls and no diet effect.

The EHP-challenge had a significant negative effect on end-point BW which was, on average, 27 % lower in the positive compared to the negative control. YANG significantly improved mean BW compared to the positive control (+7.9 %) via a lower prevalence of shrimp severely compromised in weight (Fig; 7 % and 21 % of shrimp with a BW below 1.6 g in the YANG and positive control respectively).

Accordingly, mean EHP-load was reduced in the YANG compared to positive control at all time-points (Table a). This reduction was significant at day 5 post-challenge (- 63.8 %) when the mean infection load peaked in all groups. Accordingly at day 5, the proportion of shrimp with a high EHP-load was 15% lower, and with low EHP-load 11% higher, in the YANG group compared to the challenged control (Table b).

The trial further validated the EHP-challenge model by cohabitation and confirmed that the disease causes stunt growth but not mortality in isolation. YANG applied preventively and over an EHP challenge period can contribute to reducing the severity of the EHP-outbreak, related loss of growth and occurrence of 'runt' shrimp. In practice, preserving crop-size uniformity has strong benefits by facilitating subsequent stock and pond management while preserving the crop duration and stock potential value.