Manipulation of estrus in the mare

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Manipulation of estrus in the mare
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The Estrous Cycle
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Why do it?

• Unnatural breeding season.
• Improve fertility after foaling.
• Breed more mares to a particular stallion
• Synchronize for AI and ET
• Breed mare and keep her in competition
• Keep mare out of heat while competing
• Goal of one pregnancy per service

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Unnatural breeding season

• Natural breeding season centers around Summer
  solstice
• Artificial season centers around Spring equinox

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Improve fertility after foaling

• Foal heat is the first estrus after foaling
• Usually 5 -12 days after foaling
• Affected by time of year
• Mares that have early foal heat are harder to get
  in foal than mares that have later foal heat
• Affected by management
• Short cycle after early foal heat
• Delay foal heat with progestagens
• Dont breed mares that ovulate before day 10

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Ways to alter cycle

• Artificial light
• Drugs

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Artificial light

• Begin 16 hours total light beginning Dec 1 to
  have mares cycling by Feb 15
• 1 hour pulse of light 18.5 hours after sunup
• 200 watt bulb in 12 x 12 stall
• Pregnant mares should be under lights to prevent
  anestrus in early foaling mares
• Eliminate shadows

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Drugs used in breeding programs

• Gonadotropin releasing hormone (GnRH)
• Deslorelin (Ovuplant)
• Oxytocin
• Estrogens
• Progestogens
• Human Chorionic Gonadotropin (HCG)
• Prostaglandins (PGF2a)
• Ergonovine
• Bromocriptine
• Domperidone
• Sulpiride

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Deslorelin (Ovuplant)

• Synthetic GnRH
• Used to induce ovulation
• Implant injected subcutaneously
• Implant when follicle is gt 30 mm
• 80 of follicles ovulate within 48 hours
• Extends interovulatory period
• Removal of implant prevents problems

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Oxytocin

• Causes uterine contraction and milk letdown
• Used to induce labor
• Retained placenta
• Aid uterine involution after foaling
• Expel fluid from uterus

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Estradiol cypionate (ECP)

• Estrogen compound
• jump mares
• Makes mare receptive to stallion for semen
  collection for AI
• Prepare uterus for embryo transfer

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Bio release Progesterone in oil

• Long acting progesterone
• Different strengths
• Pregnancy maintenance
• Given every 7 -10 days intramuscularly (IM)

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Human Chorionic Gonadotropin (HCG)

• Induce ovulation
• Give when follicle is 35 mm
• Ovulation usually 36-48 hours later
• May cause mare to form antibodies and not be
  responsive in later heats

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Prostaglandin F2a(Lutalyse) (Prostin)

• Causes lysis of corpus luteum
• Shortens interovulatory period
• Persistent CL
• Short cycle after foal heat
• Induce abortion

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Progesterone estradiol-17ß(PE)

• Shorten late Spring transition
• Delay foal heat
• Synchronize mares for AI ET

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Regumate (altrenogest)

• Shorten late Spring transition
• Delay foal heat
• Suppress estrus in show mares
• Synchronize mares for AI ET
• Maintain pregnancy
• Embryo transfer recipients
• Problem mares
• Questionable
• Mummified fetus

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Domperidone(Equidone)

• Increases prolactin secretion
• Fescue toxicity agalactia
• Oral paste given daily starting 10-15 days before
  foaling

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What can you do about transitional estrus

• Artificial lighting
• Progestagens
• Human Chorionic Gonadotropin (HCG)
• Wait for regular cycles