Relationship between delayed onset of egg production and involution of the bursa of Fabricius in White Leghorn chickens.

The relationship between delayed onset of oviposition and involution of the bursa of Fabricius is described. Chickens studied were 26 weeks of age and had not come into production. The bursae of nonlaying chickens were compared with those of age-matched chickens that had laid the first egg 1, 9 to 11, or 24 days before. The bursae from the nonlaying chickens were similar in weight and morphology to the functional bursae of immature pullets. Bursae of laying chickens, even on the day of the first egg, were markedly involuted. Age of the chicken was not a factor in determining bursal involution. The onset of egg production was directly related to bursal involution.