COOPERATIVE EXTENSION SERVICE UNIVERSITY OF KENTUCKY COLLEGE OF AGRICULTURE, FOOD AND ENVIRONMENT, LEXINGTON, KY, 40546 ASC-201 Avian Female Reproductive System Jacquie Jacob and Tony Pescatore, Animal Sciences nyone raising poultry for While mammals typically give Although the embryo has two ova- eggs, whether for eating or birth to their offpsring, the off- ries and oviducts, only the left pair forA incubation, should have an spring of birds develop outside (i.e., ovary and oviduct) develops. understanding of the reproduc- the body of the parents—in eggs. The right typically regresses during tive system. This will help them When carried in the womb, mam- development and is non-functional understand any problems that may malian embryos receive their daily in the adult bird. There have been occur and how to correct them. requirement for nutrients directly cases, however, where the left ova- The avian reproductive system is from their mother via the placenta. ry and oviduct have been damaged different from that of mammals. For birds, however, all the nutri- and the right one has developed to Nature has designed it to better ents that will be needed for the replace it. suit the risks associated with being embryo to fully develop must be Theovary is a cluster of devel- a bird. Unless you are a bird of prey provided in the egg before it is laid. oping yolks or ova and is located (a hawk, eagle or falcon), you are The female reproductive system midway between the neck and the faced with the fact that everyone is of the chicken is shown in Figure tail of the bird, attached to the trying to eat you. Being close to the 2. It is divided into two separate back. The ovary is fully formed bottom of the food chain requires parts: the ovary and the oviduct. when pullet chicks hatch, but it is the development of unique strate- In almost all species of birds, very small until the chicks reach gies for feeding and reproducing— including chickens, only the left sexual maturity. At hatch, pul- all while retaining the ability to fly ovary and oviduct are functional. let chicks have tens of thousands (Figure 1) of potential eggs (i.e., ova) which The reproductive strategy of theoretically could be laid. Most most mammals, especially primates of these, however, never develop (such as chimpanzees, apes and gorillas), is to produce only a few offspring and devote a considerable amount of time to caring for them. Once they are full grown and ready to take care of themselves, the par- ent’s job is complete. Birds (with some exceptions, of course) have developed a strategy where they produce multiple off- spring and tend to their needs for only a short period of time before tossing them into the wind, some- times literally. The amount of time they devote to caring for their off- spring depends on whether they are precocial (well developed at hatch) Source: PoultryHub or altricial (under-developed when hatched), with the latter requiring Figure 1. The internal organs of the female chicken. more post-hatch parental care. Agriculture and Natural Resources • Family and Consumer Sciences • 4-H Youth Development • Community and Economic Development EXTENSION to the point of ovulation. So the egg’s nutritional value or flavor. A this part since it gives the vision of maximum number of eggs a hen slight degree of yolk mottling is the infundibulum waiting for the can lay is determined when she normal and is not typically noticed ovum to fall into it, which is not hatches since no new ova are added by consumers. A high incidence of the case. Instead the released ovum once the chick has hatched. yolk mottling, however, adversely stays in place and the muscular Each ovum (singular form of affects consumer acceptance. The infundibulum moves to surround ova) starts out as a single cell use of cottonseed meal (which it. The ovum or yolk remains in the surrounded by a vitelline mem- contains gossypol) and sorghum infundibulum for 15-18 minutes. brane. As the ovum develops, yolk (which contains tannin) in the diet Fertilization, if it is going to occur, is added. The color of the yolk can also increase the incidence of takes place in the infundibulum. comes from fat soluble pigments mottling. A calcium deficient diet The next section of the oviduct called xanthophylls contained in will also have the same effect. is the magnum which is 13 inches the hen’s diet. Hens fed diets with The female reproductive system long and is the largest section of yellow maize, or allowed to range is sensitive to light exposure, espe- the oviduct as its name implies on grass, typically have dark yellow cially the number of hours of light (from the Latin word for “large”). yolks. Hens fed diets with white in a day. The release of the next ova The ovum or yolk remains here 3 maize, sorghum, millet or wheat typically occurs 30-75 minutes af- hours during which time the thick typically have pale yolks. The color ter the previous egg has been laid. white or albumen is added and the of the yolks from these hens can be If the egg was laid too late in the chalaza is formed. improved by the addition of mari- day the next ovulation will wait till The third section of the oviduct gold petals to provide the desired the next day and the hen will have is the isthmus which is 4 inches level of xanthophylls in the yolk. a day when she does not lay an egg. long. The developing egg remains Ovulation is the term used for The second major part of the here for 75 minutes. The isthmus, the release of the mature ovum female chicken’s reproductive sys- as its name implies, is slightly from the ovary into the second tem is the oviduct. The oviduct is a constricted (The term “isthmus” part of the female reproductive long convoluted tube (25-27 inches refers to a narrow band of tissue system, the oviduct. During ovula- long when fully developed) which connecting two larger parts of an tion the ovum, which is enclosed is divided into five major sections. anatomical structure). The isthmus in a sack, ruptures along the suture They are the infundibulum or fun- is where the inner and outer shell line or stigma (see Figure 3). Oc- nel, magnum, isthmus, shell gland, membranes are added. casionally the vitelline membrane and vagina. The next section of the oviduct is damaged and pale spots or The first part of the oviduct, the is the shell gland or uterus. The blotches develop on the yolk. This infundibulum or funnel, is 3-4 shell gland is 4-5 inches long, and is referred to as mottling. Al- inches long, and engulfs the ovum the egg remains here for 20 plus though the appearance of the yolk released from the ovary. “Funnel” hours. As its name implies, the is changed, there is no effect on the is an inaccurate choice of name for shell is placed on the egg here. The Stigma Figure 2. Parts of the reproductive tract of Figure 3. Ovary of a female chicken. Jacquie Jacob. a female chicken. Jacquie Jacob. shell is largely made up of calcium about 25-26 hours. This includes of albumen added and two eggs are carbonate. The hen mobilizes about 3½ hours to make the albu- encased together within a new shell. calcium from her bones to provide men, 1½ hours for the shell mem- Such eggs are so rare that no one 47% of the calcium for the shell. branes, and about 20 hours for the knows exactly why they happen. The remainder of the required shell itself. Another egg problem that is calcium is supplied by the feed. Ovulation of a yolk for the next commonly noted if you raise your Pigment deposition, if there is any, egg in a clutch occurs 30-75 min- own chickens is blood and meat is also done in the shell gland. utes after the hen lays the previous spots. Blood spots are normally The last part of the oviduct is egg, and so that each day the hen found on or around the yolk (Fig- the vagina which is about 4-5 gets later and later in her timing. ure 4). The main cause is a small inches long and does not really play As an analogy, she runs behind, break in one of the tiny blood ves- a part in egg formation. The vagina like a clock that is improperly sels around the yolk when it is ovu- is made of muscle which helps adjusted. Eventually she gets so far lated. High levels of activity during push the egg out of the hen’s body. behind schedule that she would the time of ovulation can increase Thebloom or cuticle is also added have to lay eggs after dusk. Since the incidence of blood spots. Meat to the egg in the vagina prior to hens do not typically ovulate late spots are usually brown in color oviposition (the laying of the fully in the day, the next ovulation is and are more often associated with formed egg). delayed until at least the next day the egg white. They are formed Near the junction of the va- and egg laying is interrupted. This when small pieces of the wall of gina and the shell gland, there delay results in the break between the oviduct are sloughed off when are deep glands known as sperm clutches and the cycle repeats itself the egg is passing through.