| Line 178: |
Line 178: |
| | * Progesterone levels peak 7-8 days after ovulation and decline quickly from day 18. | | * Progesterone levels peak 7-8 days after ovulation and decline quickly from day 18. |
| | * When progesterone levels fall to low basal levels, the negative feedback on the pituitary gland is removed. This allows a sudden release of gonadotrophins. | | * When progesterone levels fall to low basal levels, the negative feedback on the pituitary gland is removed. This allows a sudden release of gonadotrophins. |
| − |
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| − |
| |
| − | [[Category:Oestrous Cycles]]
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| − |
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| − |
| |
| − | == Ewe ==
| |
| − |
| |
| − | === Oestrous Cycle ===
| |
| − |
| |
| − | * Short day breeders (oestrous cycles commence in response to decrease in day length).
| |
| − | * In Britain, sheep cycle from October-February, during which time there are 8-10 recurrent oestrous cycles.
| |
| − | * Ewe lambs and yearling ewes have shorter breeding seasons than older ewes.
| |
| − | * The length of the oestrous cycle is about 17 days.
| |
| − | * Duration of oestrus in most British breeds is ~30 hours and is at least 10 hours in immature ewes.
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| − | * In merino sheep, behavioural oestrus (heat) may last 48 hours.
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| − | * Ovulation occurs towards the end of oestrus.
| |
| − |
| |
| − | === Cyclic Changes in the Ovaries ===
| |
| − |
| |
| − | * Ovaries are smaller than those of the cow and their shape is more spherical.
| |
| − | * During anoestrus they measure approximately:
| |
| − | ** 1.3 cm pole-pole
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| − | ** 1.1. cm from the fixed edge to the free margin
| |
| − | ** 0.8 cm from side to side
| |
| − | * Transrectal ultrasound is difficult, because the ovaries are difficult to access. Therefore, folliculogenesis is much harder to visualise than in the cow.
| |
| − | * The ewe is similar to the cow, with 3-4 follicular waves in each oestrous cycle.
| |
| − | ** If there are 3 follicular waves, two will occur during the luteal phase and one during the follicular phase.
| |
| − | * Even during anoestrus, dominant follicles will reach the same size as those present during cyclical activity.
| |
| − | * At the onset of oestrus, one or more follicles reach a size of 1cm.
| |
| − | ** Follicular walls are thin and transparent.
| |
| − | * Rupture of the follicle at ovulation is preceded by the elevation of a small papilla above the general surface.
| |
| − | * Ovulation occurs through rupture of this papilla ~24 hours after the onset of heat.
| |
| − | * There is rapid development of the corpus luteum.
| |
| − | ** Development is linear from day 2-12 after ovulation.
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| − | * By day 5 of dioestrus, the corpus luteum is 0.6cm in diameter.
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| − | * It then attains a maximum size of 0.9cm diameter and has a central cavity.
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| − | * Over the period of dioestrus, the colour changes from blood red to pale pink. The size stays constant until the onset of the next oestrus.
| |
| − | * At the onset of the next oestrus:
| |
| − | ** Regression of the corpus luteum of the previous cycle is rapid
| |
| − | ** Colour changes to yellow and then brownish-yellow.
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| − | * The luteolytic mechanism is similar to in the cow.
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| − | ** At the end of dioestrus, under the influence of oestradiol and progesterone, there is an increase in the number of uterine oxytocin receptors.
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| − | ** At the same time, the corpus luteum produces oxytocin, which stimulates PGF2α. PGF2α then acts to stimulate the release of oxytocin in a feedback loop mechanism.
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| − | * The first corpora lutea formed after the first ovulation at the start of the breeding season have a shorter lifespan than subsequent ones.
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| − | * In twin ovulations, the two corpora lutea can occupy the same or opposite ovaries.
| |
| − | * During pregnancy:
| |
| − | ** The corpus luteum is 0.7-0.9 cm in diameter.
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| − | ** It is pale pink in colour
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| − | ** The central cavity that is seen in cyclic corpora lutea has disappeared and is filled with white tissue.
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| − | * Ovulation with corpus luteum formation but without heat may occur in the anoestrus period. This is known as spurious ovulation.
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| − | * The number of ova shed at each oestrus is dependent on genetic and nutritional factors.
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| − |
| |
| − | === Endocrine Changes during the Oestrous Cycle ===
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| − |
| |
| − | * Just before the onset of oestrus, there is a rise in oestrogens, particularly oestradiol 17β.
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| − | * This is follwed by an LH surge, which peaks at ~14 hours before ovulation.
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| − | * At the same time as LH peaks, there is a rise in FSH.
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| − | * There is also a second peak in FSH two days after ovulation.
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| − | * Progesterone concentrations closely follow changes in the corpora lutea.
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| − | ** Maximum progesterone concentrations are lower than those of the cow.
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| − | * Prolactin fluctuates throughout the oestrous cycle.
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| − | ** Concentrations rise during oestrus and ovulation
| |
| − | ** This pattern reflects the role of prolactin in formation of the corpus luteum.
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| − |
| |
| − | [[Category:Oestrous Cycles]]
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| − |
| |
| − | == Nanny Goat ==
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| − |
| |
| − | === Oestrous Cycle ===
| |
| − |
| |
| − | * Breeding season in Britain is August-February with greatest activity in October, November and December. However, closer to the equator, does will cycle all year round.
| |
| − | * Polyoestrous
| |
| − | * Interoestrous interval of 20-21 days, but this is irregular at the start of the breeding season.
| |
| − | * Duration of oestrus is 30-40 hours.
| |
| − | * Ovulation occurs 12-36 hours after the onset of oestrus.
| |
| − |
| |
| − | === Cyclic Changes in the Ovaries ===
| |
| − |
| |
| − | * Ovaries vary in shape, depending on the stuctures present.
| |
| − | ** The longest dimention is ~2.2cm.
| |
| − | * The largest follicles reach a maximum diameter of ~1.2cm.
| |
| − | * When these follicles protrude from the surface of the ovary, they often have a bluish tinge.
| |
| − | * There are four follicular waves of growth, with ovulation occuring during the fourth wave.
| |
| − | * Corpora lutea are pink in colour
| |
| − |
| |
| − | === Endocrine Changes during the Oestrous Cycle ===
| |
| − |
| |
| − | * Endocrine changes are the same as in the ewe.
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| − |
| |
| − |
| |
| − | [[Category:Oestrous Cycles]]
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| − |
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| − |
| |
| − | == Sow ==
| |
| − |
| |
| − | === Oestrous Cycle ===
| |
| − |
| |
| − | * The domestic sow is generally polyoestrous, but the wild pig is a seasonal breeder with the main breeding season occuring in autumn with another peak in April.
| |
| − | * There is some influence of photoperiod on reproduction in the domestic sow.
| |
| − | ** Anoestrus occurs more commonly in summer and less commonly in February and March.
| |
| − | ** Ovulation rate is lower in summer.
| |
| − | ** Artificially reducing the day length from May-August will decrease the interval from weaning to oestrus from 23.6 days on average to 5.7 days.
| |
| − | * The oestrous cycle normally lasts 21 days, interrupted only by pregnancy and lactation.
| |
| − | ** During lactation, the physical stimuli of suckling will suppress cyclic activity.
| |
| − | * Oestrus normally lasts ~53 hours.
| |
| − | * Ovulation occurs 38-42 hours after the onset of oestrus.
| |
| − | * Many sows show an anovulatory oestrus 2 days after farrowing.
| |
| − | * When weaning occurs at 5-6 weeks, oestrus occurs within 4-6 days.
| |
| − | * Earlier weaning results in a slightly longer interval before subsequent oestrus.
| |
| − |
| |
| − | === Cyclic Changes in the Ovaries ===
| |
| − |
| |
| − | * The ovaries of a mature, cyclic sow are large and look like mullberries.
| |
| − | ** Surface lobulations are due to elevations of large follicles and corpora lutea.
| |
| − | * When mature, follicles reach a diameter of 0.8-1cm.
| |
| − | * When mature, corpora lutea reach a diameter of 1-1.3 cm.
| |
| − | * It is difficult to study follicular dynamics in a sow because it is hard to identify a single follicle due to the large number present.
| |
| − | * Except during the follicular phase, there is continuous proliferation and atresia of follicles.
| |
| − | * There is normally a pool of about 50 follicles 2-5mm in diameter at any one time.
| |
| − | * Between day 14-16 of the cycle,there is follicular recruitment under the influence of gonadotrophins.
| |
| − | ** This is possible due to a decline in progesterone, and subsequent withdrawal of negative feedback.
| |
| − | * A large number of these recruited follicles are destined for ovuation.
| |
| − | * At day 21-22 it is possible to identify the pre-ovulatory population.
| |
| − | * The growth of pre-ovulatory follicles during this follicular phase is associated with rapid atresia of small follicles. There is also a block to replacement of atretic follicles within the proliferating pool, so there must be some ovarian control mechanism. What exactly this mechanism is is currently unknown, but various substances have been proposed, including:
| |
| − | ** Steroids
| |
| − | ** Growth factors
| |
| − | ** Growth factor binding proteins
| |
| − | ** 'Follicle regulatory protein'
| |
| − | * The ripe follicle is a 'se-shell pink' colour. It has a fine network of surface blood vessels and one point which is very transparent. This transparent point indicates the site of imminent ovulation.
| |
| − | * Haemorrhagic follicles are common.
| |
| − | * After ovulation, a considerable number of follicles ~ 0.4cm remain on the ovary. Some of these enlarge gradually to 0.9cm by day 18.
| |
| − | * Immediately after ovulation, the ruptured follicle is seen as a congested depression on the ovary.
| |
| − | * Accumulation of blood clot soon gives the ruptured follicle a conical shape.
| |
| − | * By day 3 after ovulation, its cavity is filled with a dark red blood clot.
| |
| − | * By day 6, the blood clot is replaced by a connective tissue plug, or slightly yellow fliud.
| |
| − | ** Clots may persist up to day 12.
| |
| − | ** Fluid may persist up to day 18.
| |
| − | * Corpora lutea attain maximum size at 12-15 days post-ovulation.
| |
| − | * After this, they gradually regress to the next oestrus.
| |
| − | * They are dark red up to day 3.
| |
| − | * They then change colour and remain 'wine red' up to day 15.
| |
| − | * As the corpus luteum regresses between days 15-18, the colour rapidly changes to yellow, creamy yellow or buff.
| |
| − | * The mechanism of luteolysis is not fully understood in the sow.
| |
| − | ** Corpora lutea are unresponsive to PGF2α until 12-23 days after ovulation.
| |
| − | ** During luteolysis, corpora lutea are invaded by macrophages.
| |
| − | ** Macrophages produce Tumour Necrosis Factor (TNF).
| |
| − | ** TNF and PGF2α probably work together to cause luteolysis.
| |
| − | ** TNF also inhibits oestradiol production, thus eliminating the luteotrophic source.
| |
| − | * There is rapid regression of corpora lutea at the next oestrus, but throughout the next dioestrus the corpora lutea remain as distinct entities.
| |
| − | * After this they rapidly regress to grey pin-head foci on the ovary.
| |
| − | * During the luteal phase of the cycle, oestrogens are luteotrophic. This may prolong the lifespan of the corpora lutea for several weeks. The result of this is pseudopregnancy.
| |
| − |
| |
| − | === Endocrine Changes during the Oestrous Cycle ===
| |
| − |
| |
| − | * Oestrogens start to rise at the time of corpora lutea regression.
| |
| − | * Oestrogens reach a peak about 48 hours before the onset of oestrus.
| |
| − | * The ovulatory LH surge occurs at the start of oestrus, 8-15 hours after the peak in oestrogen.
| |
| − | * LH concentrations remain low and fluctuate throughout the rest of the cycle.
| |
| − | * FSH value vary considerably, but there are two surges.
| |
| − | ** One surge is concurrent with the LH peak.
| |
| − | ** A larger surge occurs on day 23 of the cycle.
| |
| − | * Progesterone concentrations closely follow changes of the corpora lutea.
| |
| − | ** In the first 8 days post-ovulation, there is good correlation between progesterone concentrations and the number of corpora lutea present.
| |
| − | ** By day 12 post-ovulation, the correlation is less obvious.
| |
| − | * There are two surges of prolactin.
| |
| − | ** One surge occurs at the same time as the LH and oestrogen surge.
| |
| − | ** A second surge occurs during oestrus.
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| − |
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| − |
| |
| − | [[Category:Oestrous Cycles]]
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| − |
| |
| − |
| |
| − | == Bitch ==
| |
| − |
| |
| − | === Oestrous Cycle ===
| |
| − |
| |
| − | * Monoestrous, with no seasonal influence.
| |
| − | * A single very long cycle, follwed by a long period of anoestrus.
| |
| − | * Cycle about 3 times every 2 years.
| |
| − | * The luteal phase is about the same length as gestation (~60 days), so pregnancy does not affect the length of the oestrous cycle. Thus, no luteolytic mechanism is required.
| |
| − |
| |
| − | ==== Pro-oestrus ====
| |
| − |
| |
| − | * Characterised by vulval oedema, swelling and sanguinous discharge.
| |
| − | ** May not always be visible because some bitches will continually lick the perineum.
| |
| − | * Bitch is attractive to males, but will not accept them.
| |
| − | * Duration is ~9 days
| |
| − |
| |
| − | ==== Oestrus ====
| |
| − |
| |
| − | * Accepts the male
| |
| − | * Vulva becomes less oedematous
| |
| − | * Vulval discharge lessens and becomes more clear.
| |
| − | * Duration is ~9 days
| |
| − | * Ovulation usually occurs 1-2 days after the onset of oestrus.
| |
| − | ** Some follicles continue to ovulate 14 days later.
| |
| − |
| |
| − | ==== Metoestrus ====
| |
| − |
| |
| − | * Starts when the bitch will no longer accept the dog.
| |
| − | * There is dispute over the duration of this phase, with two main theories:
| |
| − | ** Ends when corpora lutea have regressed at 70-80 days.
| |
| − | ** Ends when endometrial repair is complete at 130-140 days.
| |
| − |
| |
| − | ==== Anoestrus ====
| |
| − |
| |
| − | * Transitions from metoestrus to anoestrus with no external signs.
| |
| − | * This is also true after parturition.
| |
| − | * Lasts about 3 months before return to pro-oestrus.
| |
| − |
| |
| − | === Cyclic Changes in the Uterus ===
| |
| − |
| |
| − | * The [[Uterus - Anatomy & Physiology#Endometrium|endometrium]] shows considerable change during the oestrous cycle.
| |
| − | * In pro-oestrus and oestrus, endometrial glands are loosely coiled with obvious lumina and a deep epithelial lining.
| |
| − | * During metoestrus, the glands become larger. Lumina become smaller and the basal layer of the [[Uterus - Anatomy & Physiology#Endometrium|endometrium]] becomes more tortuous.
| |
| − | * As the bitch reaches anoestrus, there is a reduction in the number of glands and the amount that they coil.
| |
| − | * In metoestrus (~98 days after the onset of oestrus), there is desquamation of the [[Uterus - Anatomy & Physiology#Endometrium|endometrial]] epithelium.
| |
| − | * By day 120-130, the [[Uterus - Anatomy & Physiology#Endometrium|endometrium]] is restored by proliferation of cells from crypts of the endometrial glands.
| |
| − |
| |
| − | === Cyclic Changes in the Ovaries ===
| |
| − |
| |
| − | ==== Anoestrus ====
| |
| − |
| |
| − | * In anoestrus, the ovaries are oval and slightly flattened.
| |
| − | * In a medium sized breed, they measure approximately:
| |
| − | ** 1.4cm pole-pole
| |
| − | ** 0.8 cm from the attached end to the free border
| |
| − | * No follicles can be seen.
| |
| − | * On section, tiny remnants of the corpora lutea of previous cycles are visible as yellow/brown spots.
| |
| − |
| |
| − | ==== Pro-oestrus ====
| |
| − |
| |
| − | * Developing follicles are about 0.5cm in diameter.
| |
| − | * They enlarge until ovulation, where their size is 0.6-1cm.
| |
| − |
| |
| − |
| |
| − | ==== Oestrus ====
| |
| − |
| |
| − | * By the time of ovulation, the ovary is enlarged.
| |
| − | * The size of the ovary depends on the number of ripe follicles present.
| |
| − | * The shape of the ovary becomes irregular due to the projection of follicles from its surface.
| |
| − | * The follicle wall is thick, so it is hard to distinguish between follicles and corpora lutea.
| |
| − | * Prior to ovulation, the surface of follicles shows a slightly raised papule. This is about the size of a pin-head. Also, the epithelium covering this papule is brown, whereas the rest of the follicle is flesh-coloured.
| |
| − | * A unique feature of the bitch follicle is the thickness of its wall.
| |
| − | ** Due to hypertrophy and folding of granulosa cells which is visible to the naked eye.
| |
| − | ** This is evidence of pre-ovulatory luteinization.
| |
| − | * Spontaneous ovulation usually occurs 1-2 days after oestrus onset.
| |
| − | * Most follicles rupture over a period of 48 hours.
| |
| − | * The oocyte can be fertilized for up to 108 hours after ovulation.
| |
| − |
| |
| − | ==== Metoestrus ====
| |
| − |
| |
| − | * At first, the corpus luteum contains a central cavity.
| |
| − | * By day 10 after ovulation, the cavity becomes filled by compact luteinised cells.
| |
| − | * At this time, the corpus luteum reaches its full size, measuring 0.6-1.0 cm.
| |
| − | * Corpora lutea comprise the greater mass of the ovary.
| |
| − | * Generally, equal amounts of corpora lutea are found on each ovary.
| |
| − | ** The number of foetuses in the uterine horns frequently differ from the number of corpora lutea on the ovaries of their respective sides.
| |
| − | ** Embryonic migration to the uterine horn of the opposite side is common.
| |
| − | * On section:
| |
| − | ** Corpus luteum is yellow-pink
| |
| − | ** It remains unchanged in the non-pregnant bitch until about day 30 after ovulation.
| |
| − | ** It then slowly atrophies
| |
| − | ** During pregnancy, corpora lutea persist at their maximum size thoughout the pregnancy, but regress rapidly after parturition.
| |
| − |
| |
| − | === Appearance of the Ovaries on Ultrasound ===
| |
| − |
| |
| − | * Developing antral follicles can be seen at the beginning of pro-oestrus.
| |
| − | ** Appear circular and anechoic
| |
| − | * In oestrus, antral follicles are increased in size, reaching a maximum diameter of 4-13mm on day 13 (day 0 is the onset of pro-oestrus).
| |
| − | * From day 10 onwards, walls of the follicles become thickened due to pre-ovulatory luteinisation.
| |
| − | * No evidence of follicular collapse associated with ovulation.
| |
| − | * 25-30 days after the onset of pro-oestrus, the ovaries are difficult to identify.
| |
| − |
| |
| − | === Endocrine Changes during the Oestrous Cycle ===
| |
| − |
| |
| − | * The luteal phase is prolonged compared to other species, this is shown by persisting levels of progesterone in the bloodstream.
| |
| − | * Progesterone levels begin to rise 60-70 hours before ovulation has occured. This is evidence of pre-ovulatory luteinisation of mature follicles.
| |
| − | * The pre-ovulatory rise in progesterone may signal the bitch to accept the male.
| |
| − | * Oestrogens rise rapidly before the onset of standing oestrus.
| |
| − | * The LH surge rapidly follows and lasts longer than in other species.
| |
| − | * Ovulation occurs 24-96 hours after the LH surge.
| |
| − | * FSH levels peak at the same time as the LH surge.
| |
| − | * As progesterone levels fall towards the end of metoestrus or pregnancy, prolactin increases.
| |
| − | * Prolactin is a major luteotrophic hormone in the bitch.
| |
| − |
| |
| − | === Pseudopregnancy ===
| |
| − |
| |
| − | * Almost all bitches show some evidence of pseudopregnancy during metoestrus.
| |
| − | ** Covert pseudopregnancy: where the bitch is in metoestrus, but shows little or no signs.
| |
| − | ** Overt pseudopregnancy: where the bitch shows signs ranging from slight mammary development and lactogenesis to mock-parturition with nesting, loss of appetite, straining, emotional attachment to inanimate objects and heavy lactation.
| |
| − | * There is no difference in progesterone concentrations in bitches with or without pseudopregnancy.
| |
| − | * Prolactin is probably responsible for initiating the changes.
| |
| − |
| |
| − |
| |
| − | [[Category:Oestrous Cycles]]
| |
| − |
| |
| − |
| |
| − | == Queen ==
| |
| − |
| |
| − | === Oestrous Cycle ===
| |
| − |
| |
| − | * Seasonally polyoestrous
| |
| − | * Long day breeders with a period of anoestrus beginning in late autumn.
| |
| − | * Increasing daylight is the most important factor for inducing the resumption of reproductive activity. The first oestrus will usually occur soon after the shortest day of the year.
| |
| − | * If constant 14 hours of daylight is provided, the queen will continue to cycle all year round.
| |
| − | * Some non-pedigrees have regular oestrous cycles lasting about 3 weeks, but others show no regular pattern.
| |
| − | * Duration of oestrus is 7-10 days regardless of mating.
| |
| − |
| |
| − |
| |
| − | * Oestrogen concentrations increase dramatically at the time of oestrus and may double over 24 hours.
| |
| − | * The principle oestrogen is Oestradiol 17β.
| |
| − | * The rise in Oestradiol 17β corresponds with behavioural oestrus, there are no external signs of pro-oestrus.
| |
| − |
| |
| − | === Mating and Ovulation ===
| |
| − |
| |
| − | * The queen is an induced ovulator, so [[Cat Copulatory_Behaviour - Anatomy & Physiology|mating]] is important in triggering ovulation.
| |
| − | * There are receptors in the vulva, which are stimualated by [[Cat Copulatory_Behaviour - Anatomy & Physiology|copulation]].
| |
| − | * This results in release of LH fromt he anterior pituitary gland.
| |
| − | * Only 50% of queens ovulate after a single mating, because multiple ovulations are usually required for adequate LH release.
| |
| − | * The ovulatory LH surge begins within minutes of coitus.
| |
| − | * LH peaks within 2 hours, then returns to basal levels within 8 hours.
| |
| − | * Further matings before the peak in LH will result in further LH release.
| |
| − | * After multiple matings over 4 hours or more, further matings will not result in any further LH release.
| |
| − | ** Due to depletion of the pituitary pool of LH, or the pituitary becoming refractory to further GnRH stimulation.
| |
| − | * Once significant quantities of LH are reached, all ripe follicles will rupture (all or nothing response).
| |
| − | * Occasionally, ovulation will occur in the absence of contact with an entire tom.
| |
| − | ** Receptors similar to those in the vulva are found in the lumbar area.
| |
| − | ** These can be stimulated if the queen is mounted by other females or castrated cats.
| |
| − |
| |
| − | === Pseudopregnancy ===
| |
| − |
| |
| − | * Sterile matings induce ovulation and result in pseudopregnancy.
| |
| − | * Progesterone concentrations are similar to those of pregnancy for the first 3 weeks.
| |
| − | * After this, progesterone levels gradually fall and reach baseline at 7 weeks.
| |
| − | * Oestrus will occur shortly afterwards.
| |
| − | * Nesting behaviour and lactation are rarely seen, but hyperaemia of the nipples is as evident as in pregnancy.
| |
| − | * Appetite may increase, and fat may distribute to create an increased abdominal size.
| |
| | | | |
| | | | |
| | [[Category:Oestrous Cycles]] | | [[Category:Oestrous Cycles]] |