Avian Breeding, Ovulation and Oviposition - Anatomy & Physiology

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Breeding Cycles

• Classified according to length of cycle and the time of year when the species becomes reproductively active.
  • Continuous breeders are reproductively active throughout the year e.g. Khaki Campbell duck.
  • Most wild species that breed in temperate, subarctic and arctic zones display yearly cycles.
• Tropical or desert species may breed with cycles less than a year, at 6-month intervals or when conditions are favourable (opportunistic breeders).

• Usually lay one or more eggs in a clutch and terminate laying to incubate the eggs.
• Number of eggs per clutch and total number of clutches vary with species and season.

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Endocrine Control

• In females, FSH is mainly responsible for follicular growth.
• Developing follicles produce Oestrogen from Theca and interstitial cells and Progesterone from Granulosa cells.
• Increasing levels of Oestrogen stimulate an LH surge to cause the follicle to split and release the primary oocyte.
• Oestrogen mobilizes calcium from the bone, increasing plasma concentrations for egg formation.
• Progesterone secretion continues to inhibit further ovulation and stimulate behavioural changes associated with broodiness and incubation.
• Prolactin stimulates the production of crop milk in male and female columbiformes.
• Oviposition is controlled by prostaglandins and Arginine Vasotocin.

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Ovulation

• Number of ovulations varies with species, mostly lay one clutch a year.
• Infundibulum catches the oocyte, facillitated by the left abdominal air sac which tightly encloses the ovary.
• Once ovulation has taken place, the follicle shrinks and regresses.
• No corpus luteum remains, as there is no developing embryo to maintain.

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Oviposition

• Expulsion of the egg
• Contraction of the Uterine shell gland (Vagina) with relaxation of abdominal muscles.
• Minutes to hours
  • Cuckoos lay their eggs in seconds so they can get away before the host returns.

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Post-Lay

• Enters a non-breeding state whilst incubating and caring for the brood.
• Resting ovary appears shrunken, similar to the juvenile ovary.
• Oviduct regresses into an inconspicous, narrow tube.