Sexual Cycle in Mares

Sexual Cycle in Mares

• Usually reach puberty at 12-24 months of age.

• In mares, which are among the seasonally polyestric animals, the onset of sexual activity is related to daylight length.

• Increasing daylight length inhibits melatonin secretion.

Melatonin has an antigonadotropic effect in mares and a negative relation with GnRH. In short, when daylight length increases, blood melatonin level decreases and its negative effect on gonadotropic hormons is removed.

• With GnRH effect, hypophysis is stimulated and secretes FSH resulting in beginning of follicular development.

• In mares, ovulation occurs 1-2 days before estrus ends.

Ovulation occurs later in mares when compared to other

species.

There are several reasons of the ovulation occuring later in mares:

• FSH; Different from other species the sensitivity of follicles to FSH is lower, this results in requirement for a longer duration of FSH stimulus.

• LH; Because of the gradual increase in LH level, follicular maturation is delayed.

• Ovarium Structure; Because the outer layer of ovaries is coated with medulla and ovulation only occurs from a specific site called fossa ovulationalis, follicular development upto this site takes time.

Sexual Cycle in Mares

Phases of sexual cycle in mares:

• Proestrus (2 days)

• Estrus (5-7 days)

• Metaestrus (2-3 days)

• Diestrus (10-12 days)

• Anestrus (seasonal)

Sexual Cycle in Mares

Proestrus

• Lasts 2-3 days.

• is the phase in which Graaf follicle develops under the effect of FSH and estrogen starts to be secreted in increasing amounts by theca cells.

• In this phase; oviductal cells develop, veins in uterine mucosa increases and vaginal epithelium thickening increases.

• By the end of proestrus, mares usually show interest in stallions.

Sexual Cycle in Mares

Estrus

• Estrus duration is longer than other species, lasting 5-7 days.

• Most important estrus signs are; when the stallion is seen, tail is lifted, vulvar labia are opened and clitoris is revealed and stands in front of the stallion and allows mating.

• Ovulation occurs 1-2 days before estrus ends.

• Vaginal mucosa is moist, covered with a thin watery mucous, hyperemic and bright.

• Mares usually display estrus 9-12 days after parturition.

This is called foal heat.

Sexual Cycle in Mares

Metaestrus

• Lasts approximately 2-3 days.

• After ovulation, the granuloza cells rapidly luteinize and form corpus luteum. From this structure progesteron secretion starts.

• Secretion of mucus reduces and endometrium glands rapidly develop.

• In the last half of metaestrus uterus becomes softer.

Sexual Cycle in Mares

Diestrus

• is the longest phase and lasts 10-12 days.

• The mature corpus luteum on the ovaries reach maximum size on the 14th day of the cycle.

• Genital organs are under the influence of progesterone. Endometrium is thickened, uterus glands are hypertrophic and cervix is tightly closed.

• At the end of this phase corpus luteum begins to regress, uterus glands get smaller and become atrophic.

Sexual Cycle in Mares

Anestrus

• Mares enter anestrus during november to february.

• In this phase, hypothalamus and hypophysis are in essence not functional.

• In this phase, no LH secretion can occur while FSH secretion continues on a minimal level in mares.

• Uterus is small and loose, vaginal mucosa is pale and cervix is tightly closed.

Sexual Cycle in Mares

Sexual Cycle in Dogs

• Dogs are monoestric animals.

• The increase in FSH secretion when proestrus is approached results in follicular development. Blood estrogen level increases with the secretion from developing follicles.

• While the increase in estrogen level inhibits FSH secretion through inhibin, it initiates LH secretion.

• LH causes follicular luteinization and results in progesterone secretion in estrus.

• Different from other species, while a rapid increase is seen in

blood progesterone level, estrogen levels are observed to be

rapidly decreasing in dogs. As a result, estrus signs are

formed under progesterone influence.

• Ovulations occur within 48-72 hours after LH secretion and after that corpus luteum forms with LH effect and starts secreting progesterone.

• Corpus luteum continues to secrete progesterone, independant from pregnancy, untill 50-70th days.

• The progesterone levels increase to 0,6-1,0 ng/ml during late proestrus from a basal level of 0,2-0,5 ng/ml, and increase upto 1-3 ng/ml during the LH peak. After 120th day following the LH peak it returns to the base level of 0,3-0,4 ng/ml.

• For determining the timing of the cycle within a year, blood prolactin level is important. The decrease in prolactin level plays an active role on initiation of proestrus.

Sexual Cycle in Dogs

Approximate estrus intervals in some dog breeds

• German Shepherd5 months

• Boxer 8 months

• Sivas Kangal 6 months

• Scottish Terrier 6.5 months

• Pekingese 7.7 months

Sexual Cycle in Dogs

Phases of sexual cycle in dogs:

• Proestrus (9 days)

• Estrus (9 days)

• Diestrus (65 days)

• Anestrus (120 days)

Sexual Cycle in Dogs

^Proestrus

• is the duration starting from the first observation of blood in the vulva and ending at the acceptance of coitus, and lasts approximately 9 days.

• is the starting period of sexual activity of dogs.

• Some sexual reflexes are observed in dogs in proestrus;

the opening and closing of vulvar lips when the skin around vulva is touched or patted, crouching with hind legs bending towards the midline.

• Uterus is twice its normal size and the blood vessels are evident.

Sexual Cycle in Dogs

^Estrus

• starts with the female dog accepting coitus and lasts approximately 9 days.

• The bloody discharge during proestrus transforms into a hay coloured discharge.

• Searches for the male for coitus and the pheromone secretions are at the maximum level.

• Ovulations usually start occuring spontaneously 2-4 days after the start of estrus. The discharged ovum is a primary oocyte and it differentiates into secondary oocyte within the next 48-72 hours and becomes mature.

Sexual Cycle in Dogs

^Diestrus

• is the period from the end of estrus upto anestrus and lasts approximately 65 days.

• Metaestrus starts and ends within the estrus period because ovulations and forming of corpus luteum occur in estrus.

• Pregnancy in dogs depends on ovarian based progesterone.

• Serum progesterone and prolactin levels are high in dogs both pregnant and not pregnant.

• Along with this, serum relaxin levels are higher than 3,0 ng/ml in pregnant dogs while it is lower than 0,3 ng/ml in not pregnant ones. This forms an important criteria for pregnancy diagnosis.

Sexual Cycle in Dogs

Anestrus

• is sexual rest period.

• Bitch that has given birth or finished the diestrus period enters this phase without any clinical signs.

• Duration is variable, approximately 120 days.

Sexual Cycle in Dogs

Sexual Cycle in Cats

• Cats are seasonally polyestric animals.

• They reach puberty at 4-6 months or sometimes 8-9 months of age. In cats that live in houses, with the effect of white lights, estrus may be seen throughout the year.

• Season of coitus and parturition is between december and june. Ideal age for coitus is 1,5-7 years of age.

• Ovulation is provoked, occurs after coitus.

• In cats, onset of estrus is controlled by the pineal gland.

• Melatonin released from the pineal gland inhibits GnRH. The proestrus phase of the estrus cycle begins 20-60 days following the removal of the supressive effect of melatonin on GnRH with the effect of increasing daylight.

• Follicular development accelerated with proestrus, estrogen concentration increases to 20 pg/ml by the first day of proestrus from below 15 pg/ml. . In estrus it could increase to 100 pg/ml

Sexual Cycle in Cats

In cats, estrus cycle is dependant on coitus. There are 4 different outcomes:

1. If there is no ovulation during estrus, anovulatory cycle occurs (7-10 days estrus and then after 3-7 days interöstrus and after estrus sings appear again ).

2. Coitus may occur without ovulation (7-10 days estrus and then after 3-7 days interöstrus and after estrus sings appear again).

3. If ovulation occurred but fertilization did not, it results in pseudopregnancy (40-50 days).

4. Ovulation and fertilization may take place and results in pregnancy (58 days).

Sexual Cycle In Cats

Proestrus

• is the phase in which female draws attention of male but does not allow coitus.

• Lasts 1-3 days and is shorter when compared to other species. May be unnoticed.

• There is NO vulvar swelling or bloody discharge like seen in dogs.

Sexual Cycle in Cats

Estrus

• is accepted as the coitus phase. Starts with female accepting the male and ends with rejection.

• With ovulation Estrus signs duration in cats last for 2- 5 days. Cats can mate 20-36 times during estrus.

• Without ovulation Estrus signs duration in cats last for 7-10 days

interestrus

• is the phase of follicular regression after an estrus where no ovulation takes place. Lasts 3-7 days and cats do not display sexual behaviour.

Sexual Cycle In Cats

• In cats which ovulate but pregnancy does not occur pseudopregnancy is usually observed.

• After pseudopregnancy corpus luteum is formed

• In pseudopregnant cats, the luteal activity starts 4 days after coitus and 1-2 days after ovulation.

• In pseudopregnancy cases the forming of corpus luteum starts 24 hours after and is completed in approximately 37 days. The signs dissapear in approximately 45 days.

Sexual Cycle in Cats

Anestrus

• With the decrease in daylight length, transition to anestrus begins.

• is the sexual rest phase.

• In this phase; while estrogen and progesterone levels are pretty

low, prolactin level is high.

Sexual Cycle in Cats

Sexual Cycle in Pigs

• Pigs are poliestric aminals.

• In females which reach puberty GnRH secreted by hypothalamus stimulates FSH and LH and initiates the sexual cycle.

• FSH initiates follicular development inovaries. In each cycle, 10-20 follicles reach preovulator size.

• The increase in blood estrogen level, with the estrogen secreted from granulosa cells during follicular development results in display of some physical and psycological signs of estrus.

• High concentrations of estrogen stimulates the frontal lobe of hypophysis through inhibin with negative feedback and stops FSH release.

• Later on, the highest peak of LH occurs within the first 6

hours of estrus and results in ovulation.

Phases of sexual cycle in pigs:

• Proestrus 2-3 days

• Estrus 2-3 days

• Metaestrus 3 days

• Diestrus 12 days

Sexual Cycle in Pigs

Proestrus

• is the phase in which there is a significant increase in ovarian activity and with FSH effect a rapid follicular development occurs.

• With the effect of estrogens released from follicles, females display some behavioural differences specific to estrus.

Sexual Cycle in Pigs

Estrus

• is the acceptance period for mating and lasts approximately 2,5 days (60 hours)

• Vulvar lips are edemous and soft, mucosa is moist and hyperemic.

• Sometimes a cervical originated discharge may be present.

• Displays mounting behaviour similar to cows.

• In pigs ovulation occurs within estrus and around 36-40 hours after onset of estrus.

Sexual Cycle in Pigs

Metaestrus

• This phase starts with the end of accepting coitus.

• With the LH effect, the luteal cells at the ovulation site form corpus luteum.

• In this phase estrogen and progesterone levels are low.

Sexual Cycle in Pigs

Diestrus

• is the phase in which corpus luteum actively secretes progesterone, and is the longest phase of the cycle.

• Lasts approximately 12 days, if pregnancy is not formed, the corpus luteum regresses with the effect of prostaglandin F

 secreted from the uterus.

• The decrease in blood progesterone level with the luteal regression, the negative feedback effect on hypothalamus and hypophysis is removed.

Sexual Cycle in Pigs