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estrous cycle of mare.ppt - P

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									The Estrous Cycle of Mare
its Manipulation & Artificial
          Control

     Dr. Hatem Atalla D.V.M PhD
        An-Najah National University
       Faculty of Veterinary Medicine
                  2009
         Seasonality

 Their season is initiated as the ratio of daylight to
  darkness increases and ends during decreasing day
  lengths.
 The average season for horses, extending from
  February(2) to November(11). Peak fertility is
  obtained if mares are bred between May(5) and
  July(7).
 Behavioral estrus occurring during short-day months
  (January to April) is frequently not accompained by
  ovulation.
                    Seasonality
The physiologic (natural) breeding season of the mare
  occurs in late spring and summer.




   During the Transition from anestrus to physiologic
    polyestrus, the mare will frequently have variable
    length periods of behavioral signs of estrus without
    developing follicular structures or ovulating.
        J    F      M   A     M     J   J    A   S     O      N      D




     Neuropathway           Receptors in eye         Neuropathway



Decreasing melatonin          Pineal gland           Increasing melatonin



  Increasing GnRH            Hypothalamus            Decreasing GnRH



   Increasing                                        Decreasing
   Gonadotropins            Anterior pituitary       gonadotropins
   (FSH, LH)


                                 Ovaries
                             Anestrus
   Anestrus is caused by the secretion of melatonin, which is secreted in
    response to increasing darkness. The melatonin inhibits GnRH, so the FSH
    and LH are low.
   Anestrus occurs around Winter solstice.
   About 80% of mares undergo anestrus.
   Mares in anestrus are passive to the stallion advances.
   On rectal palpation the ovaries are small, smooth, and inactive.
   The cervix and uterus are flaccid.
   Vaginoscopic exam reveals a cervix that is pale and dry, and the cervix
    may even be open.
   The hormones are all at very low concentrations.
   If the is nutrition poor, the mare may not cycle back in the spring.
                 Spring transition
   The increasing daylight length in the spring brings
    about a series of changes in the mare.
       Decrease of Melatonin secretion 
       As the melatonin decreases, GnRH resumes secretion, and
        FSH and LH also increase.
   With increased FSH, follicles start to grow.
       Most of these follicles are not steroidogenically competent
        so they do not produce estrogen.
       They also do not ovulate. In fact, an average of 3.7 waves
        of follicular development occur before the first ovulation.
       After several waves, an estrogen producing follicle finally
        develops and ovulates.
       The first ovulation of the season, on the average, occurs
        about April 8
    Physiological Breeding Season
   21 day inter-ovulatory interval (estrous
    cycle)
     Estrus   (heat): 5 – 7 days
        Ovulation:   24 to 48 hours prior to end of heat
     Diestrus:   14 – 16 days
                          Fall transition
 Fall transition mirrors spring transition.
 You see:
       prolonged heats,
       irregular cycles,
       large 'hung' or 'autumn' anovulatory follicles.
            These follicle become atretic and the mare goes into anestrus.
 This is caused from the low LH release because
  melatonin is taking its grip again as the day length
  decreases.
 There is no treatment for fall transition.
Estrous Cycle of the Mare
Endocrinology of the Estrous Cycle
        Mating Behavior
         (Estrus signs)
   The mare will allow the stallion to
    smell and bite.
   She will
       extend her hind legs,
       lift her tail to the side and
       lower her rump.
       The erect clitoris will be exposed
        frequently by contractions (winking)
        of the labia.
       The vulva will be elongate and
        swollen, with the labia partly
        everted.
   The mare should be teased by a
    stallion for accurate detection.
       Attempts to fight the stallion indicate
        she is not in estrus even though
        some other signs of estrus are
        apparent.
            Timing of Insemination
                   “Mares”
 Best results without palpation are obtained by multiple
  breedings starting on the third day and repeating at
  48-hours intervals until the mare is no longer in
  estrus.
 When only one breeding is desired it is recommended
  that the mare be palpated and bred when she has a
  35mm follicle. She should be palpated 2 days later to
  see if ovulation occurred and if not, she should be
  rebred.
 When two large follicles are detected by palpation,
  mares should not be bred, since pregnancies
  involving twins are usually terminated by abortion.
 Some breeders inject LH at the time of breeding to
  insure ovulation while sperm are viable.
                 Foal Heat
 Mares will come into estrus from 7 to 12
  days after parturition (foaling heat) and can
  frequently be bred with good results.
 However, mares should be bred at this time
  only if they have been given a careful
  examination to determine if there has been
  adequate recovery since parturition.
 If there is any question about recovery, wait
  until the next estrus, which will occur about
  30 days postpartum.
  Criteria Mares Should Meet In Order to Be
            Bred During Foal Heat
 Delivery of foal without significant difficulty.
 Pass placenta within 3 hrs after birth
 A healthy foal that stands and nurses within 1
  hr.
 A cervix free from bruises and abnormal
  discharges.
 A uterus significantly reduced in size, without
  fluid accumulations.
    Estrus Manipulation Methods
           lighting
 Artificial
 Shortening Late Transition
 Inducing Ovulation
 Estrus synchronization
 Estrus Synchronization & Ovulation
  Induction
             Manipulation Methods:
                     Light
  Light can be supplemented in the afternoon and evening to
  give a total of 16 hours light each day.
1. 200 watts for a 12 x 12         Aged mares (greater than 10
     Stall X 60 days, start Dec 1   yrs) take ~12-18 days longer
2. 20 watts, 12 x 12 Stall X       No advantage to starting
     75 days                        before Dec 1
Hormone Management
   - Progestagens

   Regumate
       Oral
       Suppresses estrus by
        forming an artificial luteal
        period.
       Dose - 1 ml/50 kg orally or       Injectable
        in feed for 14 days.               progesterone
       Heat occurs 4-5 days after                suppression
                                            Estrus
        withdraw
                                        100 mg/day prevents
                                         estrus and ovulation.
         Progesterone or related
              compounds
 Regumate – most
  common
 Normalization of estrus
 Regulation of estrus
 Estrus synchronization
 Long-term suppression
  of estrus
 Delay foal heat
 Pregnancy maintenance
               PGF2
       Lutalayse or Estrumate

 Shorten  the interval between
  estrous periods
 Treatment of a maintained
  corpus luteum
 After foal heat
 Estrous synchronization with
  prostaglandins
    Hormone Management
   Prostglandins
       Only works on mature corpus  Lutalyse
        luteum (~ 5 d after ovulation)     Dose is 5-10 mg (1-2 cc/mare)
       Mare will come into heat 2-5        IM.
        days later.                        Side effects
       Ovulation in 8 - 9 days
                                        Estrumate
       The time to estrus varies
        depending on follicular            Dose is 200 mcg/mare IM.
        development on the ovary.          Fewer side effects
                                           Side effects can be sever in
                                            mare
                                              Sweating
                                              Abdominal cramps, increased
                                               motility of GI tract and/or colic
                                              Increased heart rate
                                              Muscle weakness and balance
                                               problems
                                              All side effects begin at 5 - 10
                                               minutes and last until 60
                                               minutes after injection
              Induction of Ovulation
 hCG                                  Deslorelin
    Dose 1,500-3,000 IU IV              3.5 cm follicle, ovulate 36-48
    3.5 cm follicle                      hrs, 90%
                                         As effective as hCG without
    Ovulation normally occurs            antibodies
     within 36-48 hours.
    80% of mares will ovulate
     within 48 hr
    Older Mares loose 13-15 %
    More you use it, the less
     effective it becomes on
     subsequent heats
    10% less effective Feb, Mar,
     Apr
                      Estrogen

 Limited   use:
   “Induction     of estrus” for jump mare
     Estradiol cypionate; 5-10 mg
     Start 3-4 days prior to wanting mare showing signs
      of estrus
   “Enhance      signs of estrus” in silent heats
     Estradiol   17B; 1-2 mg
Suppress Estrous

 Sterile, 30 to 35 mm diameter glass marble into
  the uterus within 24 hrs after ovulation
 Increases the interovulatory interval from 21
  days to ~ 90 days for about 40 to 70% of mares
 Appears to be no discomfort, nor any
  detrimental effects on future breeding prospects

								
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