Strongyles

Anemia, dry coat, diarrhea, general loss of condition

Roundworms

Loss of condition, bowel problems, or colic when present in large numbers; migrating roundworm larvae can also injure the lungs in young horses

Pinworms

Horse rubs its tail; itching and irritation around anus; discharge and worms visible around anus

Bots

Loss of condition and colic from large numbers in the gut; occasional diarrhea or constipation

Tapeworms

Mild diarrhea, colic, failure to grow or put on weight as expected