I've used both water bottle and oral treatment. The oral treatment is highly effective (so Ive found) but it is harsher. I would cut your treatment short by a week if you are actively breeding. Tylan does affect fetal development. Rats treated for two weeks or longer seem to loose fetal weight and drop a smaller number of pinks. Some are effected more so than others by Tylan. I had one female drop 15 with no issues and another who lost fetal weight and dropped 4.