You need to check with your veterinarian on the best de-worming/parasitic control medication for the swans. We have used several but the usage depends on the type of parasite you are trying to eradicate. An overall de-wormer may rid the birds of certain tapeworms, roundworms, etc., but may not rid the birds of the parasite gigardia. Fecal and blood testing by your veterinarian can pinpoint the actual parasite and if the birds even have the parasite. Finally, the dosage is based upon weight of the birds and too much of the medication can cause serious illness and even death in the birds. The Regal Swan