The Estrous Cycle of Mare its Manipulation

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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

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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.

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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.

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J F M A M J J A
S O N D
Increasing day length Light Stimulus
Decreasing day length
Receptors in eye
Neuropathway
Neuropathway
Pineal gland
Decreasing melatonin
Increasing melatonin
Hypothalamus
Decreasing GnRH
Increasing GnRH
Increasing Gonadotropins (FSH, LH)
Decreasing gonadotropins
Anterior pituitary
Ovaries
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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.

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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

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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

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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.

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Estrous Cycle of the Mare
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Endocrinology of the Estrous Cycle
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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.

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Timing of InseminationMares

• 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.

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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.

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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.

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Estrus Manipulation Methods

• Artificial lighting
• Shortening Late Transition
• Inducing Ovulation
• Estrus synchronization
• Estrus Synchronization Ovulation Induction

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Manipulation MethodsLight
Light can be supplemented in the afternoon and
evening to give a total of 16 hours light each
day.

• Aged mares (greater than 10 yrs) take 12-18 days
  longer
• No advantage to starting before Dec 1

1. 200 watts for a 12 x 12 Stall X 60 days, start
   Dec 1
2. 20 watts, 12 x 12 Stall X 75 days

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Hormone Management - Progestagens

• Regumate
• Oral
• Suppresses estrus by forming an artificial luteal
  period.
• Dose - 1 ml/50 kg orally or in feed for 14 days.
• Heat occurs 4-5 days after withdraw

• Injectable progesterone
• Estrus suppression
• 100 mg/day prevents estrus and ovulation.

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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

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PGF2? Lutalayse or Estrumate

• Shorten the interval between estrous periods
• Treatment of a maintained corpus luteum
• After foal heat
• Estrous synchronization with prostaglandins

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Hormone Management

• Prostglandins
• Only works on mature corpus luteum ( 5 d after
  ovulation)
• Mare will come into heat 2-5 days later.
• Ovulation in 8 - 9 days
• The time to estrus varies depending on follicular
  development on the ovary.

• Lutalyse
• Dose is 5-10 mg (1-2 cc/mare) IM.
• Side effects
• Estrumate
• Dose is 200 mcg/mare IM.
• 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

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Induction of Ovulation

• hCG
• Dose 1,500-3,000 IU IV
• 3.5 cm follicle
• Ovulation normally occurs 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

• Deslorelin
• 3.5 cm follicle, ovulate 36-48 hrs, 90
• As effective as hCG without antibodies

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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

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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