How many ovaries does a pig have

The cervix is a muscular junction between the vagina and uteri. It is the site of semen deposition during natural mating and AI.

It is dilated during heat estrus but constricted during the remainder of the estrous cycle and during pregnancy. The vagina extends from the cervix to the vulva and serves as a passageway for urine and the piglets at birth.

The bladder is connected to the vagina by the urethra. The vulva is the external portion of the reproductive tract. It often becomes red and swollen just prior to estrus and this swollen condition is usually more pronounced in gilts than in sows. The hypothalamus located at the base of the brain secretes gonadotropin releasing hormone GnRH which regulates the anterior pituitary gland to secret FSH Follicle Stimulating Hormone and LH Luteinizing Hormone into the blood which stimulates the production of the ovarian hormones, estrogen and progesterone, which in turn regulate the reproductive process.

Oxytocin is released from the posterior pituitary gland. Non-pregnant and non-lactating sows and gilts display estrus or standing heat on a regular basis throughout the year. The estrous cycle is normally 21 days and is defined as the time between the onset of one estrus to the onset of the next. The cycle length can range from days. Lactation or the nursing stimulus inhibits the estrous cycle and sows will not, as a rule, return to heat until the litter is weaned.

Days from weaning until estrus is influenced by such factors as length of lactation, parity, season and nutritional level, but should range from 4 to 7 days. As estrus or heat approaches, follicles or "blister like" structures form on each ovary. Follicular growth accelerates about 3 days before estrus and is influenced by FSH or follicle stimulating hormone released from the pituitary gland, located at the base of the brain.

A maturing ovum is held within each follicle. Granulosa cells within the follicle secrete estrogen, a hormone, which among other things is responsible for the typical signs of estrus. Ovulation, or release of the ova, is stimulated by LH. Ovulation occurs about 40 hours after the onset of estrus, but this interval is variable. Several factors can influence ovulation rate or number of ova shed. Sows may ovulate ova while gilts may ovulate ova.

Flushing increased energy levels prior to estrus may increase ovulation rate yet may have little effect on the ultimate litter size. The white or maternal breeds generally have a higher ovulation rate. Crossbred females generally have a higher ovulation rate than either of the parent breeds. The onset and disappearance of estrus and estrus behavior is gradual and there are individual differences among females see Fig. The primary sign , and most reliable sign, of estrus is "standing" while another sow or the boar mounts.

Many females will stand for the "back pressure test" when applied by the herdsperson. A higher percentage of females will respond to the "back pressure test" if there is a boar present. Therefore, use of an intact or a vasectomized boar is an important part of a regular heat detection program. Boars secrete pheromones odors in their salivary glands which elicit the standing reflex of the female.

Mature boars are superior to young boars in stimulating this response. This is also observed in some sows after weaning at certain times of the year and under cases of excessive weight loss during lactation. Sometimes follicles develop to the large size but fail to ovulate, leading to the condition known as cystic ovary disease. There have been reports where certain factors have been shown to specifically increase ovulation rate.

In gilts, elevated feeding of dietary energy during the last 10 days before estrus and an increase in the number of lifetime estrous cycles appears to increase ovulation rate in females. Once the follicle ovulates and releases the egg, there is some bleeding from the rupture site but this quickly forms a small blood clot on the ovary where the follicle once was.

Within a few hours after ovulation, the cells of the follicle begin to rapidly change and divide into a new type of cell, which over the next few days, will form into corpus luteum cells, which produce progesterone, the hormone needed for developing the uterus, inhibiting estrus, and maintaining pregnancy.

After ovulation of all the large follicles at estrus, the egg is moved into the tube called the oviduct. This movement occurs by the coordinated muscular contractions of a thin piece of tissue called the fimbria Figure 1. The fimbria wraps around the entire ovary, and under the influence of estrogen, induces muscular contractions which propel all of the eggs into the funnel shaped opening of the oviduct. The oviduct is a short convoluted tube that connects the ovary to the uterus Figure 1.

This short tube is very important since it must propel the eggs in one direction and the sperm in the opposite direction. Fertilization takes place in the mid portion of the tube, called the ampulla. Most of the eggs reach the site of fertilization within 30 min to 1 h after ovulation. The eggs will remain viable and fertilizable in the tube for approximately h after ovulation.

Therefore it is important that insemination occur prior to ovulation so that sperm are waiting for the egg. Sperm are typically deposited into the reproductive tract near the junction of the cervix and uterus. Although much of the inseminate enters the uterus, there is a significant back-flow loss of semen volume which occurs over the next several hours after insemination. Under stimulation from uterine contractions induced by both oxytocin from the female and prostaglandins in the semen of the boar, sperm are moved to the site of fertilization.

Of the billions of sperm that are inseminated, only a very small fraction of these hundreds to thousands actually arrive at the site of fertilization. Many sperm are prevented from entering the oviduct from the uterus by a small restrictive muscle that can open and close under the control of hormones.

Therefore, only a small sperm reservoir is typically maintained in the oviduct. Some sperm cells reach the site of fertilization within minutes after insemination, however, these sperm cells are incapable of fertilizing eggs because a time dependent passage through the female uterus is required to prepare them to attach to the egg.

Most of the fertilizing sperm will reach the egg in about h after insemination, but numbers of sperm will continue to increase in the oviduct for up to about 12 h after insemination. It is important to note that the levels of estrogen and progesterone can affect the movement of the sperm and eggs in the oviduct. Excessive estrogen at this time has been reported to cause egg retention in the oviduct, while excessive progesterone has the effect of opening the oviduct and speeding entry of the sperm and exit of the eggs.

Eggs that are not fertilized usually pass into the uterus within several days. Sperm that are in the oviduct and uterus which do not fertilize eggs are destroyed by cells of the immune system over the next few days. The uterus is the largest single portion of the female reproductive tract and is capable of considerable change in size from the non-pregnant to the pregnant state. The uterus is composed of paired uterine horns with the cervix at one end and the oviducts at the other.

The uterus has four layers, an inner most layer which is glandular, two additional inner layers which are muscular, and the fourth layer, which forms the outer surface. The large muscle layers are important for propelling sperm to the oviduct, moving and spacing embryos before attachment, and for delivery of piglets at farrowing. These layers are responsive to many of the reproductive hormones and how and when contractions will occur depend upon which hormones are present.

The other important layer is the inner most glandular layer which produces and secretes hormones and nutrients for the developing embryos. After fertilization, the early embryos enter the uterus on day 4 and remain free-floating and mix with each other until approximately d Days of the cycle metaestrus : ovaries with follicles about to ovulate and newly ovulated rubrum bodies that are organizing the clot that has remained after the rupture of the follicles.

The rubrum or hemorrhagic bodies have a collapsed appearance, a conical shape and a dark red color, and they show the point through which the ovum has left the follicle.

Figure 3: Reproductive cycle and follicular and luteal dynamics diagram of the sow adapted from Hafez, ; Mc Donald, Days 5 to 14 of the sexual cycle luteal progressive phase , this phase is characterized by the secretion of progesterone by luteal bodies, whose functions are to induce the proliferation of the endometrium embryonic survival and block the development of follicles blocking FSH and LH. Days of the sexual cycle luteal regressive phase : ovaries with pale pink corpus without vascularization.

During this phase the ovary presents its minimum size and luteolysis is evident, producing a rapid decrease of progesterone to basal levels and an increase of prostaglandins.

Follicles smaller than 4mm will suffer atresia, while those larger than 4mm will continue their growth. Days 17 to 21 of the sexual cycle proestrus : it is the moment when the ovary prepares for the next cycle, the selection and growth of the dominant follicles will take place days , the pituitary secretion of FSH increases, with its subsequent fall, and followed by an increase in the concentration of estrogens that cause a preovulatory LH peak.

In this phase, large ovaries with hyperemia appear where follicles 8 mm are found, accompanying several mm albicans with a yellowish or white cream color, which will gradually disappear until they become a scar in fibrous tissue of the ovary. In next blog posts we will focus on a topic closely related to this, such as the guidelines for a correct induction of heat in the sow and the insemination technique.

Gil, M. Falceto, M. University of Zaragoza. Interamericana-Mc Graw-Hill, Previous Next. Vulva : external genital part, it is externalized with two lips, at the bottom of them is the clitoris. The vulva is highly vascularized, changing its morphological appearance during the heat, being much more inflamed and edematous.

This feature is much more marked in gilts, and it serves as one more tool to detect if a sow is in heat. Vestibule and Vagina : next to the vulva we find the vaginal vestibule and the vagina, with a variable joint length between cm, in whose caudo-ventral part is the urinary meatus.

The vagina in its cranial part connects with the cervix, has an immunoprotective function with the presence of IgA. Picture 1: Reproductive system. Cervix : it is a complex structure and because of this, desingning probes able to cross it without causing injury to it and being able to carry out the technique of post-cervical insemination acquires great importance. This structure is about cm in diameter and about cm in length and forms the gateway to the uterus. It is formed by cervical folds or tuberosities, these folds change consistency due to hormonal influence.

Remaining closed in the presence of progesterone and staying dilated during estrus. It also has a secretory function of mucous substance, which serves as lubricant at the time of mounting and protective function during pregnancy.

Picture 2: Cervical rings. Uterus : it is formed by the body of the uterus cm where it bifurcates into two uterine horns. The horns have a variable length between individuals due to various factors including race, number of births and age. They have a tortuous shape and connect the body of the uterus with the oviducts.