Comparison of oral, rectal and intraperitoneal administration of IgY antibodies in passive immunization of rainbow trout (Oncorhynchus mykiss)

IgY antibodies serve an interesting opportunity for drug administration and passive immunization. For routine application in aquaculture, oral delivery needs to be established. Two feeding trials with non-specific IgY antibodies were conducted in juvenile trout to assess IgY uptake through the intestinal wall and to identify target tissue of IgY. In experiment 1, a positive control that received the lowest effective dose by intraperitoneal injection (0.0076 mg IgY g BW−1 day−1) was compared with three groups fed a 10-, 50- and 75-fold dosage and a negative control. After 12, 24 and 36 h, plasma IgY concentrations of all treatments were below the detection threshold. In experiment 2, an excessive oral administration (200-fold) was compared with two groups that received IgY rectally at 75- and 150-fold dosage of the injected control. Blood samples taken 2, 4, 6, 12 and 24 h did not result in detectable IgY concentrations, suggesting that neither the increased oral dosage nor the bypassing of the stomach improved IgY uptake. In both experiments, only intraperitoneal injection resulted in IgY uptake, revealing a decrease from 40.33 ± 21.72 µg ml−1 after 12 h to 19.48 ± 12.67 µg ml−1 at 36 h in experiment 1 and a peak at 75.58 ± 23.75 µg ml−1 after 2 h in experiment 2. Immunohistochemistry was carried out to localize IgY in selected target tissues of IgY action. Staining revealed IgY in the liver but not in white muscle, pituitary and brain, irrespective from the time point measured.