Nucleotides are the building blocks of DNA and RNA and involved in many important physiological processes. In Penaeus vannamei, nucleotides can be supplied through the feed to support growth performance and enhance disease resistance . A first study was conducted to evaluate the effect of different inclusion levels of nucleotides on the growth, feed conversion rate , production of digestive enzymes and immunity in shrimp under non-challenged culture conditions. In a second experiment , the mortality and immune gene expression after a disease challenge with White Spot Syndrome Virus (WSSV) was analysed.
In a 8-week feeding trial at Kasetsart University (Thailand), one control diet (CTRL) and three diets with different (LOW, MED, HIGH) inclusion levels of nucleotides (extracted from bacterial cells) were tested, each in 7 replica tanks with 35 juvenile shrimp. Daily weight gain could be significant (p<0.05) improved from week 6 onwards for MED and HIGH inclusion levels. At week 8, FCR was 14% (p<0.05) lower for HIGH inclusion. Analyses of the digestive enzyme s at week 8 , showed higher activity of chymotrypsin (+38% for MED) and lipase (+63% for MED) in all nucleotide groups. After 8 weeks of feedi ng, the nucleotide groups exhibited a higher hemocyte count , hemolymph protein level and superoxide dismutase activity (Figure 1).
At IMAQUA (Belgium), after a 3-week adaptation period, a WS SV challenge test was performed with a control group and a diet containing the LOW level of nucleotides. The mortality after 14 days was reduced by 42% (p=0.07) in the nucleotide group. Furthermore, looking at the difference in relative gene expression (qPCR) during the period before and at the end of the challenge , upregulation of SOD (superoxide dismutase) was more pronounced (p= 0.08) in the nucleotide group (Figure 2). These results suggest that the immunomodulating effect of nucleotides could result in an upregulation of crucial genes, leading to higher survival rates after disease challenges.