Pharm control of Mare

Question 1

How is Artificial lighting used to change the breeding season of mares

Answer 1

• Artificial lighting
  
  • place mares under lights starting December 1
  • Add light to the end of the day
  • 14.5-16hrs of total light (lights on at 6AM and off at 10PM)
• Able to read a newspaper in all parts of the stall or paddock
  
  • 100w incandescent
  • 40w fluorescent
• Average days of estrus to ovulation is 70 days
• Mares that are due to foal early also need to be placed under lights in you plan to breed them back early

Question 2

What medications can be used to stimulate follicular development?

Answer 2

• Advance first ovulation of the year in seasonally anestrous mares
• Stimulate follicular development in non-cycling postpartum mares
• eFSH (12.5 mg, IM BID)
• reFSH (0.65 mg, IM BID)
• GnRH (deslorelin or buserelin)
  
  • 10-125 ug BID
  • Follicular development to occur in 3-5 days
    
    • ≥25 mm

Question 3

What drugs can be used to advance the breeding season?

Answer 3

• Progestagens
• Dopamine D2 antagonists

Question 4

How do progestagens work

Answer 4

• Questionable if it actually advances first ovulation
• Likely times first ovulaiton
• Altrenogest: 0.044mg/kg PO SID 12-15days (1ml/110lbs)
  
  • Estrus in 2-5 days
  • Ovulation 9-12 days after treatment
• Intravaginal progesterone-releasing devices for 10 days
  
  • CIDR-B: 1.9 g Progesterone
  • CueMate: 1.5 g Progesterone
  • Ovulation 4-8 days after removal
  • may cause vaginitis
• Requirements
  
  • Late transition
  • Follicles 20-25mm

Question 5

How does dopamine antagonists work to advance the breeding season

Answer 5

• Dopamine decreases prolactin
  
  • Prolactin is thought to increase the number of LH and FSH responsive receptors within follicles making them more responsive to LH and FSH
• Dopamine D2 antagonists increase prolactin
• Domperidone (1.1 mg/kg PO SID) or Sulpiride (0.5mg/kg IM SID)
  
  • until ovulation occurs
  • 51-85 days to ovulation under natural photoperiod
  • conjunction w/ artificial lights will speed up ovulation in transitional mares
    
    • 3 wks of lights before treatment

Question 6

Why would the interestrus period need to be shortened? How?

Answer 6

• Indications:
  
  • Shorten diestrus and induce estrus
    
    • missed ovulation
    • Dx and therapeutic
  • Estrus synchronization
    
    • donor and recipient mare
    • accommodate stallion schedule
    • groups of mares
• Prostaglandin ⇢ lutelolysis
  
  • requires a mature CL (≥5 or 6 days post ovulation)
  • Estrus in 2-5 days
    
    • depends on follicle size at treatment
    • if given with follicles of ≥30mm return to estrus may be as long as 15 days

Question 7

What Prostaglandins exists for use in mares?

Answer 7

• Dinoprost (Lutalyse^®) 5-10 mg IM
  
  • transient sweating and colic signs
• Cloprostenol (Estrumate^®) 250 um IM (off label)
  
  • lesser degree of side effects
    *

Question 8

How can multiple mares have their Estrus Synchronized?

Answer 8

• Termination of the Luteal Phase
  
  • PGF_2a
• Prolong the Luteal Phase
  
  • Progestagens
  • Progestagens + Estrogens

Question 9

How is Luteolysis achieved for Estrus Sync?

Answer 9

• PGF_2a
• Requires mature LC
  
  • 1 injection (if stage is known)
  • 2 injections 14 days apart
• Estrus 2-5 days after the last injection

Question 10

How is the Luteal Phase prolonged for Estrus Sync?

Answer 10

• Suppress estrous behavior and LH secretion
  
  • preventing follicular maturation and ovulation
• Artificially maintain elevated progesterone concentrations until CL regresses
• Stopping progestogens results in a more predictable estrus and ovulation
• Progestogens:
  
  • Altrenogest: 0.044mg/kg PO daily
    
    • for 10-14 days
  • Progesterone in oil: 100-150 mg IM SID
    
    • give for 10 days
  • Intravaginal devices: CIDR-B, CueMate
  • BioRelease long acting progesterone: 1500 mg IM q7days
  • PGF_2a given last day of treatment
    
    • Estrus 2-5 days
• Progesterone plus Estradiol 17:
  
  • 150 mg Progesterone IM + 10 mg Estradiol IM SID
    
    • 10 days
  • Progesterone inhibits LH secretion
  • Estradiol suppresses FSH
    
    • Suppression of follicular growth
  • PGF_2a last day of treatment
    
    • Estrus 2-5 days

Question 11

Why induce ovulation? How?

Answer 11

• Synchronize ovulation with mating
  
  • cooled or frozen semen
• Minimize # of matings per cycle
  
  • Liver cover
    
    • heavily booked stallion
    • Thoroughbred industry
  • minimize post-mating endometritis
• Exogenous source of LH or stimulate release of endogenous LH
• ≥ 35 mm follicle must be present

Question 12

What drugs exist to induce ovulation in mares?

Answer 12

• Human Chorionic Gonadotropin (HCG)
  
  • LH like action
  • 2500 (1500-3000) IU IV (2.5 mls)
  • Ovulation 36 hrs after injection 80% (24-48)
  • 85-95% ovulate within 48hrs
  • Refractory to hCG
    
    • Anti-hCG antibody formation after repeated doses
• Deslorelin acetate (SucroMate Equine)
  
  • GnRH analogue
  • 1.8 mg IM
  • ovulation occurs in 36-40 hrs in 80% after injection
  • Not associated with refractory development
  • ≥30 mm follicle

Question 13

Why would estrus need to be suppressed in mares?

Answer 13

• Indications:
  
  • Pain/colic during estrus
    
    • preovulatory follicle or postovulatory corpura hemorrhagica
    • Muscle relaxation under estrogen dominance
      
      • minor lameness may become more prevalent during estrus
  • Estrus-related behavior/performance problems
    
    • less cooperative or attentive during estrus
• Rule out: urogenital discomfort, submissive behavior, and stallion-like behavior

Question 14

What hormones exist to suppress estrus in mares?

Answer 14

• Altrenogest (Regumate)
  
  • 0.044 mg/kg PO SID
  • allow 3 days to suppress estrus
  • Suppression for as long as it is being administered
  • Safe for long term use
  • Concerns about human safety with handling
• Progesterone in oil
  
  • 100-150 mg IM SID
    
    • Sustained release injectable: BET laboratories
      
      • weekly to monthly injections
      • more costly than altrenogest
• Implants
  
  • Not recommended
  • Local reaction/ abscesses
  • Unreliable estrus suppression
• Depo-provera (medroxyprogesterone)
  
  • not effective
• Oxytocin
  
  • 60IU SID or BID IM day 7-14 post-ovulation
  • Prolongs CL function ~60-70%
  • 60 days (35-95)
• Plant oils:
  
  • Intrauterine infusion
  • 1ml fractionated coconut or peanut oil day 10 post-ovulation
  • prolongs CL function ~90%

Question 15

What are the surgical methods of suppressing estrus in mares

Answer 15

• Ovariectomy
  
  • permanent solution to cyclicity
  • Mares may still exhibit behavioral signs of estrus
    
    • paradoxical estrus: steroids of adrenal origin
  • If performing because of behavioral issues
    
    • assess behavior during winter anestrus

Question 16

What immunologic methods exist to suppress estrus in mares

Answer 16

• GnRH vaccine
  
  • Antibody production that binds to GnRH suppressing reproductive activity
  • effects may wear off during the second year or later
    
    • vaccinated females may become fertile
    • re-immunization can extend infertility
  • Chance of becoming permanently sterile
  • Injection of males will result in infertility

Question 17

What other methods (non surgical, hormonal, or immunologic) exist to suppress estrus in mares?

Answer 17

• Intrauterine Device (non hormonal)
  
  • Glass marbles placed in the uterus
  • 35mm sterilized
  • Placed immediately after ovulation
  • Cyclicity s suppressed by endogenously produced progesterone
    
    • extended luteal function by altering prostaglandin secretion
    • Reported to suppress for ~90days
  • Does not work in majority of mares