After addressing the typical concerns (cation-complexing,
water concentrations, and differences among
the groups) and new problems noted (water color
change and indirect linear exposure-concentration),
tetracycline water medication concentrations as dosed
were found to be consistent with tetracycline feed additive
concentrations. In one feed additive study, Kniffen
et al. (1989) dosed 4 gilts with 0.55 g of tetracycline per
kilogram of BW. Tetracycline concentrations reached
0.4 to 0.6 μg/mL (peak). Another study administered a
single water dose of tetracycline in fasted and fed pigs
(Nielsen and Gyrd-Hansen, 1996). Animals received a
dose of 45 mg/kg of tetracycline, and peak tetracycline
concentrations of 4 μg/mL were seen in fasted pigs;
however, when fed pigs were given this single oral dose,
peak tetracycline concentrations only reached 0.8 μg/
mL. These data are consistent with the data reported
by Luthman et al. (1989) on oral tetracycline use.
According to our study, if pigs consumed only 2 L of
treated water per day, then they would have received
a 25 or 50 mg/kg dose of tetracycline for the 250- and
500-mg/L treatment groups, respectively. Because it is
impractical to fast pigs in a production facility, this
information indicates that water medication values
are in line with feed additive concentrations and will
likely have similar efficacy.