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Reproductive Cycles :recycle: (Puberty And Reproductive Senescene (Puberty…
Reproductive Cycles :recycle:
Reproductive Cycles
The 2 Types Of Reproductive Cycles Are Estrous And Menstrual.
Estrous and menstrual cycle ( ovarian cycle representing the interval between 2 successive ovulation).
Estrus = period of sexual receptivity( on heat)
Estrous cycle refer to domestic animals, menstrual refer to primates- menstruation( vaginal discharge of blood).
End of the luteal phase is the 1st day of estrous cycle.
Proestrus = period of follicle development, after CL regress .
Metestrus = period of initial development of CL.
Diestrus = period of mature phase of the CL.
In dogs and cats, sexual receptivity is measured from serum progesterone level.
CL represent the culmination of follicle growth and ovulation.
Puberty And Reproductive Senescene
Puberty Is The Time At Which Animals First Release Mature Germ Cells.
Puberty is the onset of reproductive life.
In primates, 1st menstrual bleeding is the onset of puberty.
Time of 1st ovulation.
Onset of puberty = ↑[GnRH] synthesis from hypothalamus → [gonadotropin]↑ → follicle growth.
Hypothalamus is highly sensitive to -ve feedback inhibition by estrogen.
Puberty is the maturation of hypothalamus,→ decreased sensitivity to the -ve feedback inhibition.→ relase GnRH.
Photperiod is the exposure to the light.
Photoperiod allows sensitivity of hypothalamus to ↓ response to -ve feedback by estrogen →puberty onset.
Photoperiod → secretion of gonadotropin↑, follivle growth ↑.
Gonadotropin surge → promote luteinization with short life span.
Initial luteal structure die → another gonadotropin surge → ovulation → CL with normal life span, initiate ovarian activity.
Photoperiod can have suppresive effect on puberty timing in animals with light controlled ovarian activity ( cats).
Long photoperiod → male lamb lose sensitivity to estrogen feedback inhibition → promote spermatogenesis.
Reproductive Senescene In Primates Occurs Because Of Ovarian Inadequacy,Not Inadequacy Of Gonadotropin Secretion.
End of ovarian activity→ menopause.
Ovarian failure → essence → depletion of oocytes → menopause.
1st factor = follicle fails to develop from their primordial state, ↓ no. of follicles.
2nd factor = absence of gonadotropin receptors prohibits follicles entering the gonadotropin-dependent stage of growth.
Menopause initiated by irregular ovarian cycle, failure of follicle development and ovulation.
Gonadotropin secretion↑,[estrogen] ↓, ↓-ve feedback inhibition.
Reproductive senescence not recognized in domestic animals, because they are slaughtered before that happens.
Dog experience reproductive senescene, neonatal mortality ↑, as age ↑.
Sexual Behaviour
Sexual Receptivity Is Keyed By The Hormones Estrogen and Gonadotropin- Releasing Hormone In The Female And Testosterone In The Male.
Sexual behavior depends on exposure/ no exposure of hypothalamus to testosterone during neonatal period.
Testosterone cause masculiniation of sexual centers in the hypothalamus ( medial preoptic area).
1st principle, magnitude of [hormone] affect sexual behavior is small. ( cat)
2nd principle, synergism betwen hormones is imporyant for sexual receptiveness. (dog = estrogen priming followed by progesterone )
3rd principle, sequence of exposing to hormone is important .(ewe, progesterone priming b4 estrogen exposure → manifest estrus)
Estrogen required for sexual receptivity.
Progesterone important to sheep. Sheep must expose to progesterone, then only can respond to estrogen.
Dog = prior exposure to estrogen makes the female attractive to male,but does not produce sexual receptivity, so require exposure of progesterone for estrus.
In other domestic animals, progesterone is inhibitory for estrous activity.
Testoterone important for libido ( sexual desire) in female primate.
Degenerating follicles theca secrete androgens androstenedione and testosterone.
Androgens maintain libido in males.
Castrated animal can still have libido as they have androgen ( which is adrenal origin).
GnRH also important to sexual receptivity.(cause estrus).
↑[GnRH] synthesis, ↑ gonadotropin, ↑ preovulatory gonadotropin surge, → ovulation.
External Factors Controlling Reproductive Cycles
Photoperiod, Lactation,Nutrition,And Animal Interaction Are Important Factors That Affect Reproduction.
Photoperiod
Animals have continuous ( cylical ) ovarian activity, as well as period of no ovarian activity ( anestrus).
Cats and dogs are positively affected by ↑ photoperiod.
Goats and sheep are positively affected by ↓ photoperiod.
Negative respond to photoperiod = suppress ovarian activity .
Main translator of photoperiod is the pineal gland → produce melatonin in response to darkness.
Melatonin have +ve effect on reproductive cycles.
Sheep =↑ darkness exposure, ↑ melatonin,→ maintain ovarian activity.
Systemic implant of melatonin to sheep in spring → ↑ovarian activity, ↑no.of multiple ovulation of breeding season.
Cat is most sensitive to photoperiod change → estrus → mature antral follicles.
Suppressive effect of photoperiod can be overcomed by exposure to artificial lightning regimens.
Lactation
Lactation suppress ovarian activity.
Complete suppression in sow, do not come into estrus until piglet are weaned.
Dairy cow are not suppressed by lactation unless nutrition inadequacy.
Photoperiod can overcome lactation suppression on ovarian activity in goat and sheep.
Mare have no lactation suppresive effect on ovarian activity.
Suckling can stimulate prolactin synthesis, ↑ lactation.
Inhibiting factors ( dopamine and GAP) are suppressed by suckling.
Pheromones
Pheromones allow communication among animals through olfactory synthesis.
Sex pheromone affect sexual behavior.
Pheromone found in sebacous gland, reproductive tract and urinary tract.
“ Whitten effect”= introduce male odor to induce estrus in female, stimulates the synthesis and release of gonaotropins.
“ Bruce effect”= introduce strange male to recently bred female to block pregnancy. The strange male odor blocks the release of prolactin , CL regress → miscarriage.
Pheromones help male attracted to female at sexual receptivity period.
Methyl-p-hydroxybenzoate, isolated from vagina secretion of dog in proestrus and estrus → produce intense anogenital interest to male.
Sow assume a breeding (rigidity) stance when exposed to male’s urine.
Androgen can act as pheromones.
Male marks their territory with urine ( musk-type odor).
Human pheromone is perfume , civetone derived from civet cat.
“Whiten effect” can manipulate estrous cycle of animal.
Interaction of rams with ewes over extended [eriods of anestrus → earlier ovarian activity.
“Physical contact” → sight can influence gonadotropin secretion.
“Whitten effect” → use to influence pig puberty onset.
“Dormitory effect”→ synchronization of menstrual cycles in roommate women and bitches in kennel.
Inadequate Nutrition Results In Ovarian Inactivity, Especially In Cattle.
Dairy cow require enough feed to maintain body weight, growth and lactation.
Animals need enough nutrition to initiate ovarian activity.
Negative nutritional balance will suppress and delay ovarian activity.
Clinical Correlation
Sexual Attractiveness In Spayed Bitch.
Clinical examination
Dog is attracting male despite already undergone ovariohysterectomy.The bitch does not allow intromission. The vulva is slightly swollen with small discharge present. Vaginal smear reveals increased number of neutrophils. Suspected urogenital tract infection. Reproductive endocrine panel and urinalysis obtained show low [estrogen]and low [progesterone].Male dogs are attracted by the odors generated by urinary tract infection. The bitch does not allow intromission due to low progesterone level.
Treatment
Bladder infection is treated, keep the bitch away from other male until infection has cleared.