Equine Reproductive Physiology.

1. Physiology of Reproduction
Equine Reproduction
Puberty, estrus cycle, ovulation, semen, pregnancy,
parturition
1

2. MARES
• TERMS
• Anestrus
• Diestrus
• Estrous cycle
• Estrus
• MARE
CLASSIFICATION
• Pregnant
• Open
• Barren
• Maiden
• Wet
• Dry

3. Mare Anatomy
• Vulva
• Vagina
• Cervix
• Uterus
• Oviducts
• Ovaries
Left Ovary
Oviduct
Left Uterine
Horn
Uterine Body
Cervix
Vagina

4. Comparison of Cortex and Medulla in
Equine and Non-equine Ovary
Ovulatory Fossa
C
C
M
M
Ovulation is often said to occur on about day 5 of
cycle, or 1 to 2 days before end the of estrus

5. Male Reproduction
• Puberty (Stallion): 12-24 months
• Mating Behavior: 1.Snorting
2.Biting
3.Sniffing
4.Flehman
• Optimum Breeding Age: 3 years or older
• Seasonality During Fall/Winter:
1. Semen Volume ↓
2. Sperm Concentration ↓
3. Libido ↓
4. Motility ↔
Spring/Summer:Reverse

6. Stallion Physiology
Onset of sexual maturity 10-24 mo
Life span of sperm in female
tract
2-4 days
Survival time with fertilizing
capacity
1-2 days
Sperm output
Semen volume/ejaculate 20-100 ml
Sperm concentration X 106 30-800 ml
# sperm/ejaculate X 109 6

7. Number of Sperm Depends On:
• Seasonal Influences (Photoperiod)
– Effected Areas
• Ejaculate volume
• Sperm numbers
• Total sperm/ejaculate
• Sperm motility
• Willingness to breed
• Mounts before breeding
• Scrotal size
• Testosterone production

8. Female Reproduction
• Puberty (Mare): 10-15 mo
• Cycle Length: 21-22 d (range 19 to 25 d)
• Estrus : 5-7 days
• Diestrus (Luteal Phase + Proestrus) = 14-16 days
Seasonality
• Cyclic (Estrous) Spring (April/May)
Summer
• Acyclic (Anestrous) Fall (Varies among individuals)
Winter
• Transitional Fall Late September through
November
Spring Early March to May

11. Estrus Cycle
The normal estrous cycle in the mare is 21 to
22 days long, as defined by the intervals
between ovulation.
Diestrus has a fairly consistent 14 day
(hormonal) or 15 day (behavioral) duration.
There is really no metestrus or proestrus
during the equine estrous cycle.

12. A Brief Sequential Overview of the
Regular Estrous Cycle

13. Prediction of Ovulation
• Number of days in heat
• Growth rate of largest
follicle
– Average 3-5 mm/day
• Size of largest follicle
• Softness of preovulatory
follicle
• Ultrasound image

14. Contrasting Points
Parameters Equines Bovines
Ovary Medulla is surrounded by
cortical tissue
Cortical tissue
surrounded by
medullary portion
Site of
Ovulation
Ovulation Fossa Any site at ovary
Accessory CL Day 40 to 150 days of
pregnancy
Primary CL is
continued
LH Surge remains continuous
after ovulation
-
Ova Mare can discriminate
fertilized & unfertilized ova
-
PMSG Endometrial Cups at day 40
of Gestation
-
Interspecies
breeding
Mule -

15. Signs of Estrus
• Most consistent
– Elevated tail raise
– Winking
• Other supporting signs
– Leaning
– Squatting
– Standing still
– Urinating

16. Manipulation Methods
Artificial lighting
Shortening Late Transition
Inducing Ovulation
Estrus synchronization
Estrus Synchronization & Ovulation
Induction

17. Pregnancy Evaluation
• Ultrasound, 14-18 days
– ID twins
– ID placental
development
• Re-evaluate, 40 days
• Monitor Placental
function & fetal growth

18. Equine Gestation Period
• Varies 327 – 357 days. Avg 340 –342
days.
• Ass – horse Hybrids __ longer gestation
350 – 355 days.
• Horse (64)
• Donkey (62)
• Mule (Male Donkey x Mare),Sterile (63)
• Hinny (Horse x Ass or Female Donkey)
• Molly (rare) (Female Mule x Horse)

19. Hormones During Gestation

20. Stages of Parturition
• Stage 1
– Onset: initial uterine
contractions
– End: rupture of
chorioallantois
(water bag)
• Stage 2
– Onset: rupture of
chorioallantois
– End: delivery of
fetus

21. Stages of Parturition
• Stage 3 (< 3 hrs)
– Onset: delivery of
fetus
– End: passage of the
fetal membranes

22. Foals and Immunity
• Colostrum (first milk) -
antibodies
• 1-2 pts of high quality
colostrum
• If adequate passive transfer
occurs there will be over
400-800 mg/dl IgG in foal’s
blood
• Takes ~ 12 hours for all
antibodies ingested in
colostrum to show up in the
blood

23. Postpartum Estrus
• Foal Heat
• Fertile as compared to other species.
• Breeding may be necessary to maintain
the 12 mo. Foaling interval.
• May be necessary to back up foaling.

24. Thanks