Unit 3

Poultry Reproduction

    So far, in studying reproductive life cycle considerations, we have examined puberty, pregnancy and parturition in mammalian species in which the offspring develop inside the body of the dam and, after birth, are provided nourishment in the form of milk produced by the dam.  In the avian species, however, the dam produces an egg in which, if fertilized, the offspring will  undergo growth and development outside the body of the dam.  The dam does not suckle it's young, either.  As a consequence, there are a number of contrasts between avian and mammalian reproductive life cycles.

  Puberty and Breeding in the Avian Species

  •  The hen reaches puberty and starts to produce eggs at 4-5 months of age.  As with mammals, the reproductive system is not functioning completely normally at the onset and hens at puberty produce small egg sizes and high percentages of eggs with twin yolks.  Since these eggs do not produce viable offspring, hens are not bred to produce young until they reach 5-6 months of age.
  • The cockerel is capable of insemination at 4-5 months of age, but, like the hen, is not used for breeding until 6 months of age to insure viable sperm.
  • The natural instinct is to lay a "clutch" of eggs, become "broody", stop laying eggs (ovulating), and set on eggs to hatch.  This broodiness has, for the most part, been bred out of our commercial breeds of poultry, and hens will produce eggs continuously.  Hens do not have an estrus cycle, and will lay an egg nearly every day.
  • In contrast with mammalian species in which both ovaries are functional and either ovulate simultaneously, or alternately, 99% of hens have only one functional ovary.

Reproductive Physiology of the Hen

    The reproductive tract of the hen is also different from mammals, and different functions are performed in different segments of the tract.  The  major structures are as follows:

  • OVARY - containing immature and mature follicles.  The mature follicles consist of the egg "yolk" and the unfertilized ovum.
  •  INFUNDIBULUM - yolk  with attached ovum is snatched up by the infundibulum.  It is at this point in the reproductive tract that the ovum is fertilized if the hen has been mated with a cockerel.  Spermatozoa from the cockerel are stored in "sperm nests" located within the infundibulum and are capable of fertilizing ova for up to 30 days after mating.
  • MAGNUM -  while traveling through this part of the oviduct, the albumin or egg white is formed.
  • ISTHMUS - the tough outer membrane located just beneath the egg shell is formed in this part of the oviduct.
  • UTERUS - also referred to as the "shell gland", this is where the egg shell is formed.  Most of the transit time from ovulation until the egg is laid is spent in the uterus.
  • VAGINA - the egg travels through the vagina into the cloaca, from which it is "laid."
  • CLOACA - this is the common external opening from which the contents of the urinary tract (urates), the intestinal tract (feces) and the reproductive tract (eggs) exit the hen.

graphic depicting the female avian reproductive tract

This image was taken from the Purdue Avian Sciences web page.  For additional pictures of the reproductive tract of the hen, check the University of Georgia, Department of Poultry Sciences, PS 202 lab review materials.  Slides 68, 70, 71, 73, 77 and 84 are particularly good examples.

General Information

  • A hen is capable of producing an egg every 25 hours.
  • Eggs are produced and laid regardless of whether the hen has been mated and the eggs are fertile or not.
  • A hen is capable of laying approximately 270 eggs per year.
  • The embryo in a cracked fertile egg will not develop.
  • Incubation and hatching of fertile egg
    • humidity & temperature control are important factors in the hatchability of fertilized eggs.
    • Chicken -- eggs incubate 21 days; spend 1 day in hen; 22 days from fertilization to birth of chick
    • Turkey, duck -- eggs incubate 28 days for a total of 29 days from fertilization to birth.

In addition to differences in the reproductive physiology, the development of avian offspring differs significantly from mammals in a number of other ways:

  • The shell takes the place of the uterus or womb in providing a dark, warm, moist sterile environment in which the offspring develop.
  • The albumin or egg white serves as a shock absorber for the developing embryo, just as the amniotic fluid does within the mammalian amniotic membranes (birth sac).
  • The yolk provides nourishment to the developing chick just as the umbilical cord provides nourishment to the developing mammal.  The yolk also provides maternal antibodies to the chick to protect against infectious agents in the environment to which the hen has developed an immunity (this is similar to colostrum in mammals).
  • The chick develops outside and independent of the hen, and does not need the hen for survival provided that the proper environment is provided by man for incubation of the egg.  Mammals develop inside the uterus of the dam and are dependent upon the health and well-being of the dam throughout the entire gestation for their health and well-being.

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