Efficacy of intraperitoneally and orally administered ProVale, a yeast beta-(1,3)/(1,6)-D-glucan product, in inhibiting xenoma formation by the microsporidian Loma salmonae on rainbow trout gills

The objectives of the research were to compare the efficacy of ProVale yeast beta-glucan (beta-glucan) with that of a previously tested research-grade yeast beta-glucan preparation when administered as an intraperitoneal (IP) injection and to also pilot test the effectiveness of ProVale yeast beta-glucan as a feed additive for reducing Loma salmonae xenoma formation on the gills of rainbow trout Oncorhynchus mykiss. Rainbow trout received IP injections of ProVale (4, 10, or 20 mg of ProVale/kg of fish) or Sigma beta-glucan (4 mg/kg). Oral challenge with L. salmonae occurred 1 week after IP injection with the beta-glucan products. For the second objective, 400 rainbow trout were separated into tanks and duplicate groups were treated with 0, 50, 100, and 200 g of ProVale/1,000 kg of feed. Starting at 3 weeks prior to challenge and continuing 2 weeks after challenge, rainbow trout were fed the various ProVale doses daily at a feeding rate of 1% of the fish biomass. Commencing at 4 weeks postchallenge, the fish in each trial were evaluated for the presence of xenomas on the first left gill arch. The most protective IP dose of commercial ProVale was 10 mg/kg when compared with the laboratory-grade IP dose of Sigma beta-glucan (4 mg/kg). Both of these intraperitoneally administered beta-glucan products were effective in reducing the mean xenoma count. ProVale used as a feed coating (200 g/1,000 kg) was able to reduce the mean xenoma count by 50%.