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 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.

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.