1-MONOGLYCERIDES OF SHORT- AND MEDIUM-CHAIN FATTY ACIDS: AN INNOVATIVE APPROACH TO CONTROL Lactococcus garvieae IN RAINBOW TROUT, Streptococcus agalactiae AND Streptococcus iniae IN TILAPIA
A specific composition of 1-Monoglycerides of Short and Medium Chain Fatty Acids (from C3:0 to C12:0), available on the market with the commercial name SILOhealth 128, proved to inhibit Lactococcus garvieae, Streptococcus agalactiae and Streptococcus iniae in vitro at pH 7, that is at a pH value that we find in the gut of several aquatic species. The trial was conducted by the Public Animal Health Institute Bruno Ubertini (Forlì - Italy). The MIC of SILOhealth 128 against these bacteria was comprised in a range from 0.01% to 0.1%. Lactobacillus was not inhibited. The MIC of butyric and formic acid against the pathogenic bacteria was >1%. 1-Monoglycerides resulted to be by 10-100 folds more effective than organic acids at pH 7.
Three field trials were conducted with Oncorhynchus mykiss in three farms in North Italy.
In a pond populated with 35,000 individuals with average weight of 300g typical symptoms of L. garvieae infection were observed: exophthalmos, dark skin, lethargy and a mortality of 30-50 fish/day. Liquid SILOhealth 128 was administered at a dosage of 1% of the feed, corresponding to 100mg/kg of live weight/day; the feeding rate was 1%. After 10 days the onset of the pathology was stopped: no new individuals showed any signs of the disease; the already infected individuals were not recovered, also because they stopped eating. SILOhealth 128 was administered until the end of the production cycle, to the commercial size of 400-500g. No more out-breaks of disease were observed.
In the second trial the initial typical signs of lactococcosis were observed in two ponds populated with about 40,000 and 45,000 individuals with average weight of 330g and 270g respectively: dark skin, exophthalmos, lethargy and mortality equal to 20-30 fish/day. The feed was supplemented with 1.5% of powder SILOhealth 128 and administered immediately after the first clinical signs occurred. The L. garviae infection did not spread and did not affect other individuals; the mortality increase stopped after 4 days of SILOhealth 128 administration and decreased close to zero in 12 days. The feed was supplemented with SILOhealth 128 during the subsequent 20 days and then a feed without supplementation was given. No more lactococcosis outbreaks were observed during the production cycle.
The third trial was conducted after grading procedure of trout on 20t of biomass in total. The fish size was 1kg. After grading the fish was placed into two ponds. The high density of 80 kg/m3 and the stress facilitated the lactococcosis outbreak. Liquid SILOhealth 128 was administered at a dosage of 1.5% of the feed for 15 days and then at 1% up to the commercial size of 1.5kg. The mortality at the beginning was 30kg/day and it decreased to 10kg/day (less than 10 fish/day) in four days and remained constant up to the end of the production cycle.
In all the trials SILOhealth 128 proved to be effective in stopping lactococcosis spreading and in reducing the mortality, in some cases to zero, and prevented the recurrence of the disease until the end of the production cycle. In case of treatment with antibiotics like Erythromycin, a suspension period of 30 days must be respected before selling the fish for human consumption, with economic losses for the farmer. Furthermore, the usage of Erytromycin can create antibiotic resistance: in the farm practice it is observed that the first treatment with Erytromycin to control L. garviae infection usually lasts for 10 days. If a second treatment is required, the period of antibiotic administration may be extended to 15 days, due to the resistance created with the first treatment. SILOhealth 128 can be considered as a promising tool to control L. garviae in trout in alternative to antibiotics. Its usage is recommended in tilapia to prevent or to control infections caused by S. agalactiae and S. iniae.