Diagnosis, Prevention, and Control of French Molt

by Gary D. Butcher and Richard M. Miles

French molt is an important disease of young budgerigars characterized by abnormal feathering. The condition has occasionally been reported in young lovebirds and other psittacine species. The name “French molt” was used because the disease frequently affected offspring of budgerigars that had been imported into Germany from France.

Clinical signs of French molt usually appear about five to six weeks of age when the young birds are ready to leave the nest. Excessive molting and occasional breakage of wing and tail feathers occur at this time or shortly after the birds have been flying for a few days. The degree of feather loss reflects the severity of the disease. In severe cases, the secondary flight feathers (shorter, upper “arm” feathers) are also lost while in the most severe cases, nearly all body feathers are shed. Since affected birds are usually unable to fly, they are known as “runners”, “creepers”, or “crawlers”.

There appears to be a pattern to the feather loss. The most medial flight feathers drop out first, and they are shed symmetrically from both wings. Often, all except the two outermost primary flight feathers are lost. These feathers are the first to develop and complete their growth. Only developing feathers which are still growing are lost during an attack of French molt. This is evidenced by the appearance of dried blood spots at the sites where the feathers have fallen out.

Microscopically there is no evidence of dermatitis. The keratin of the quills is poorly developed, and there is extensive hemorrhage in the vascular pulp of the quills. The growth rate of the flight feathers is reduced.

French molt is sporadic in occurrence. The disease may appear suddenly in an aviary and affect offspring of breeding pairs at random. Individual nests may contain both affected and normal fledglings. Affected young within a nest show varying degrees of severity. Generally, after the disease appears, it continues throughout the breeding season, especially in breeding pairs which have already reared two nests of offspring.

The etiology of French molt is still a matter of speculation. Many possible causes have been postulated. These include:

  1. a nutritional deficiency or imbalance such as a protein or amino acid deficiency* in the proventricular secretions of the nursing adults:
  2. a papovavirus infection; and
  3. a budgerigar pox virus infection.

The info about nutrition added by Avianweb:

*Dietary: Poor feather condition / long molts and flaky beaks may be the result of a diet deficient in the essential amino acid “methionine.” The requirement for methionine tends to increase when accumulated levels of toxic substances in the body increase.

High levels of methionine can be found in sesame seeds, pumpkin seeds, sunflower seeds, Brazil nuts, fish, meats, eggs, as well as various lentils. Significant amounts can also be found in spinach, potatoes and boiled corn.

Supplementation is another option for birds that don’t have access or refuse to eat foods rich in methionine – such as spirulina, which is rich in this amino acid.

Once nutritional needs are met, it may take 9 to 12 months for new, better feathering and the flaky beak to be replaced with a new, smooth one.


While the actual cause of French molt is unknown, certain factors tend to increase the incidence and severity of the condition. These include:

  1. stress due to overbreeding, early breeding or out-of-season breeding;
  2. selection of birds for show at the expense of health;
  3. poor hygiene;
  4. infectious agents, dietary deficiencies and environmental stresses acting in concert;
  5. strains with a history of French molt; 6) the use of artificial lights to induce breeding during the normal off season.

Since there is no known cause for French molt, there is no specific recommended therapy. Suggestions include:

  1. supplementation of animal protein and vitamins in the diet of breeders;
  2. pulling abnormal and loose feathers to stimulate replacement;
  3. limit breeding to two clutches per breeding pair per year; and
  4. selection against French molt in the breeding program. Affected birds sometimes recover spontaneously at the first molt within 6 to 8 months of age; however, severely affected birds may never develop normal plumage.


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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. and M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

Source: edis.ifas.ufl.edu – University of Florida … Copyright Information: This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.


Polyomavirus in Budgerigars (French Molt)

By: Dr. Branson Ritchie – Edited by: Dr. Barbara Oglesbee

Section: Overview

The first generalized infection caused by any polyomavirus in any species of animal was described in young budgerigars and was called budgerigar fledgling disease (BFD). An avian polyomavirus related to the one recovered from budgerigars has been shown to infect several other species of birds. The clinical changes and progression of disease varies dramatically between budgerigars and non-budgerigar psittacine.

The polyomaviruses that infect birds are not known to infect humans or other mammals. The outcome of a polyomavirus infection in a budgerigar depends primarily on a bird’s age when it is infected. Younger birds are most severely affected. In aggressive aviary outbreaks, most infected chicks may die within a several week period.

Chicks that survive the initial phase of an infection can have abnormally developed feathers frequently referred to as French Molt. Budgerigars with abnormal flight feathers are commonly referred to as “runners.” Visibly similar feather lesions can be caused by any event that damages the blood supply to developing feathers.

In Europe a more chronic form of the disease is common, while in the United States and Canada an acute form of disease with high mortality is typical.

In some budgerigar flocks, 100 percent of the birds have been shown to have been previously infected. In other more intensively managed flocks, polyomavirus activity cannot be demonstrated in any of the tested birds.

Virus transmission is thought to primarily occur through direct or indirect contact with contaminated feather or fecal dust. Infected budgerigar hens can pass the virus through the egg.

The environmental stability of avian polyomavirus causes a considerable problem in the home or aviary.


  • Watch for signs of bruising, bleeding and sudden death in chicks.
  • Watch for signs of abnormal feather development.



There are several ways to detect polyomavirus in birds. Diagnostic tests your veterinarian may recommend include:

  • Microscopic examination of affected feathers
  • Serology (testing for antibodies)
  • Culture for avian polyomavirus — a DNA probe-based test (PCR) on choanal and cloacal swab
  • DNA probe-based test (PCR) on whole blood — a DNA probe-based test (in situ hybridization) on tissues of birds with suspicious microscopic changes


  • There is no specific treatment for polyomaviruses.
  • Fluids and supportive nutrition as needed
  • Several immune system stimulants have been suggested to help the bird eliminate the infection.
  • Vaccinate to decrease transmission and susceptibility to disease.

Home Care and Prevention

At home keep infected birds and those to which they have been exposed in isolation during recovery. Thoroughly clean and disinfect enclosures, food bowls and non-porous toys and perches. Discard porous (wood, natural fibers, rope, etc) objects that cannot be thoroughly cleaned and disinfected and do not replace them until birds are clinically normal and no longer shedding virus.

Finally, monitor fecal output to insure proper food consumption and digestion on a daily basis.

There are several things you can do to prevent polyomavirus infection. These include:

  • Vaccination
  • Reduce crowding and improve air circulation and hygiene.
  • Keep your bird out of direct or indirect contact with other birds.
  • Enjoy the bird you have. If you decide to add a new bird, it should be quarantined for at least 90 days and be examined by an avian veterinarian at the beginning and end of quarantine.
  • Have any new bird vaccinated and tested during quarantine. Quarantine any bird that has been taken from the home or aviary and exposed to other birds before placing it back in the home or aviary.
  • Use biosecure shipping containers to prevent exposure to avian polyomavirus during transport.

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Information contained on this website is provided as general reference only. For application to specific circumstances, professional advice should be sought.