Roundworms; these worms are fairly large, and measure 1 1/2 to 2″ or more in length. They are believed to compete with the pigeon for nutrients in the intestines, so in heavy infestations, roundworms can be another cause of “going light” because they absorb nutrients that the pigeon needs. In light infestations, these worms tend to gather in the upper part of the intestines, close to the proventriculus and gizzard. In heavy infestations they spread out along the entire intestinal tract and may even be found in the droppings. In large numbers roundworms can effectively block the intestines, and food has a very difficult time passing through.
Female roundworms lay many thousands of eggs regularly, so it doesn’t take long for the loft to become heavily contaminated. Soon after they are passed in droppings, eggs aren’t able to cause infection in pigeons, even if they are picked up from the floor and swallowed. The eggs need time — about 2 weeks — in damp, cool conditions for a young worm to develop. At this stage, if droppings containing eggs have contaminated feed or grit, or if birds are just picking on the floor and swallow eggs, the young worm hatches in the intestines, and over time, becomes an adult — and the cycle repeats. If loft conditions are too dry, the thick wall of the eggs protects them from dehydration, and they remain dormant until conditions for development are more favourable. They can live in this way for years if necessary.