This is also why the dosage on tranquilizer darts are also normally higher for IM injections (due to the bioavailability). Injecting tranquilizer darts into the bloodstream has 100% bioavailability. Tl;dr. Tranquilizer darts are usually meant for IM injections so the doses are higher. read more
That said, it's best to inject skittish horses in the neck, as you can't get kicked from that position. The large muscle of the hindquarters are better if you need to deliver a large volume of medication (10 ml or more), though. read more