The use of artificial insemination (AI) increased in these last years because it offers several advantages over natural mating. New genetics can be introduced into a herd with decreased health risks. The semen that is collected from the boar can be diluted in a semen extender and with one ejaculation multiple insemination doses can be created and can be used to breed several sows and gilts. This allows more extensive use of genetically superior boars, increasing the rate of genetic improvement within a herd. On farms employing artificial insemination few boars are needed, and as a consequence, feed, labour and housing costs are reduced. The major processes of AI are: semen collection, evaluation, and processing; detection of oestrus; and insemination.
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Reproductive physiology of female swine
For successful artificial insemination, heat detection of the female swine is very important. Oestrus begins with the pituitary gland, which is a gland situated just below the brain. The pituitary gland secretes hormones into the bloodstream such as the luteinizing hormone (LH) and the follicle stimulating hormone (FSH), which are called gonadotropins. In immature gilts gonadotropin secretion is low, but at 6 to 8 months of age, when there is the 1st oestrus it increases dramatically. During the 2 to 3 day period just prior to oestrus, the increase of LH and FSH cause the follicles on each of the two ovaries to grow rapidly. The follicles secrete increased levels of estradiol, which is a hormone into the blood that causes changes in behaviour and physiology of the animal. These changes are associated with the oestrus. Each follicle contains an ovum. When the ovum is released and fertilised by a sperm cell, it develops into an embryo.
The increase of estradiol concentration in the blood reaches a threshold which triggers a large release of LH from the pituitary gland around the onset of oestrus. The release of ova from the follicles into the oviducts is stimulated by the LH. On average, ovulation occurs 40 hours after the onset of oestrus. Fertilization of the ova by the sperm cells occurs in the oviducts, the tubes between the ovaries and the horns of the uterus, and then the fertilised egg moves to the uterus. The sites on the ovaries from which ova are released, then form structures that are called corpora lutea. These corpora lutea secrete the hormone progesterone into the blood. During the luteal phase of the oestrus cycle, which is approximately between day 4 and day 16, progesterone inhibits the secretion of LH and FSH from the pituitary gland, inhibiting follicular growth.
When the ova are not fertilised during oestrus or embryos do not implant in the uterus, around day 16, the uterus starts t secrete the hormone prostaglandin-F2o into the blood. This hormone causes the falling off or death of the corpora lutea. This causes the progesterone level to decline and this allows the increase of LH and FSH levels, follicle growth, and the return of oestrus. In a female swine, oestrus occurs every 18 to 22 days, unless the cycle is interrupted by pregnancy, lactation, poor nutrition, disease, etc.
If fertilisation occurs and pregnancy is initiated, the prostaglandin-F2o is not released in the blood stream. The corpora lutea are maintained and secrete high levels of progesterone into the blood stream throughout gestation. Progesterone is essential in pregnancy, as it inhibits follicular growth and uterine contractions. Around day 114 of gestation, the uterus releases a large amount of prostaglandin-F2o into the blood, and this causes the corpora lutea to regress. The progesterone level is then decreased, uterine contractions commence and the foetuses are expelled.
During lactation, when the pigs are sucking from the sow, LH and FSH are not secreted. When the suckling are weaned, a stimulus allows the secretion of gonadotropin to increase and the follicles grow rapidly and there is the corresponding rise in the circulating levels of estradiol. The sows return in oestrus in seven days after weaning and estradiol elicits the surge of LH, causing ovulation.
The detection of oestrus is very important for successful artificial insemination. The oestrus duration is variable, but the average is 38 hours in gilts and 53 hours for sows. With the high concentrations of estradiol several sign can show that the sow or gilt is approaching or is in oestrus. These signs are: a red, swollen vulva and enlarged clitoris, mucous discharge from the vulva, nervous and restless behaviour, moving back and forth along pen partitions, frequent urination, increased vocalisation, decreased appetite, mounting other females and/or standing to be mounted by other females, elevation of ears, locking knees, and elevating the back.
The best indicator that female swine are in oestrus and ready to be mated is the immobilisation response. When in oestrus they exhibit the immobilisation response as a reaction to a combination of visual, auditory, olfactory and tactile stimuli originating from the boar. It is important to put a mature boar in contact with the female swine that are being checked for oestrus. The females should be checked at least twice a day, with 12 hours interval in between for more accurate determinations. When checking for oestrus, the female should be exposed to a boar for several minutes and observed closely for several signs. If the female re checked in the morning, this should be done before or at least one hour after feeding.
Considerable energy expenditure is required for maintaining the immobilization response. If a gilt or sow that is in oestrus becomes fatigued, it may become unresponsive to boar exposure and not resume an immobilisation response for several hours. During periods when not checking for oestrus, the boar should be kept away from the females, because this greatly increases the likelihood that sows and gilts in oestrus will display the immobilisation response when exposed to the boar during the oestrus check. The boar exposure during oestrus checking should be restricted to small group of females.
When the sows and gilts are housed in crates, a boar should be moved in the front of the females, while a second herdsman applies back pressure. If the female is in oestrus it move forward and assume immobilisation response and when pressure is applied to the back it will push back. This is an effective method of detecting oestrus.
Disposable AI equipment should be used and catheters should only be used ones, so different equipment is used on different female swine to protect plant health.
Before inseminating, the vulva should be cleaned with a paper towel and the tip of the catheter should be coated with a non-spermicidal lubricant. The lips of the vulva should be spread and the breeding catheter inserted. The catheter should be angled slightly upwards while moved through the reproductive tract. This helps prevent entry into the urethra, which is the tube leading to the bladder. After wards the catheter should be slid gently through the vagina until the operator feels resistance. The resistance indicates that the catheter has reached the cervix. With a spirette-type catheter the instrument should be turned counter-clockwise until it locks into the cervix. Then to remove the spirette, it should be turned clockwise while gently pulled outwards. With a foam-tipped catheter, firm forward pressure should be applied to the catheter until the bulbous tip is locked into the cervix, and to remove the bulbous catheter tip, it should be pulled outwards gently.
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After the semen and extender is mixed gently, the semen bottle, tube, or bag should be connected to the open end of the catheter. The semen is dispensed by gently squeezing the container over a three to five minute period, taking care to avoid excessive back flow of the extended semen out of the vulva. The tip of the catheter may be blocked against cervical tissues occasionally, blocking the flow of the semen, and if this happens the catheter should be repositioned by turning it.
The insemination is easier if the female swine is exhibiting the immobilisation response, although it is not necessary. If a boar is placed in an adjacent pen, it can facilitate AI, but on the other hand, immobilisation response requires considerable energy expenditure and the female may become fatigued. When there is a large number of sows to be bred, some of them may become refractory to the boar stimuli prior to artificial insemination.
When the boar is present during artificial insemination, the sow’s pituitary gland releases oxytocin into the bloodstream, which a protein hormone. It stimulates muscles contractions of the uterus and oviducts, and these contractions cause the semen to be drawn into the reproductive tract during AI. This is also known as self insemination. If the AI technician applies firm back pressure and rubs the flank or udder of the sow during insemination, he will facilitate the self insemination.
Timing of insemination
Accurate oestrus detection is the success of artificial insemination. Timing of insemination is normally based on the time when oestrus is first detected. Insemination should be done prior to ovulation, i.e. maximum 24 hours before ovulation in sows and maximum of 12 hours before ovulation in gilts. Inseminating twice during oestrus increases the likelihood that one will occur during the optimum time. If female swine are in standing heat for 3 days, a third mating should be beneficial. The females that are not in oestrus should not be inseminated because reproductive performance will be adversely affected.
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