Equine Estrus cycle Flashcards
The mare has what type of estrus cycle?
Seasonally polyestrus
Long day breeders- Melatonin influenced
Anestrus- winter- Nov-Feb
Transition- spring- Feb-Mar
Estrus- summer- Mar-Sept
Transition- fall- Sept-Nov
Variable!
Some cycle year round
Young, good BCS
Climate
Short day effect on hormones in the mare
Increased melatonin secretion -> Decreased GnRH
Direct mechanism unknown
FSH secretion does NOT change
LH is at basal levels (lower than when cycling)
-Follicular growth diminished
-Estradiol concentrations low
During short days in mares, melatonin secretion is increased leading to a decrease in GnRH and this effects FSH and LH…
FSH secretion DOES NOT CHANGE
LH levels decrease to basal levels
Long day effects on hormones in the mare
Decreased melatonin secretion-> Increased GnRH secretion
Continued FSH secretion (Small follicle development)
Increased LH surge activity
-Increased follicular activity
-Increased size
–Early on: not enough for follicular maturation
Factors that influence the horses seasonal estrus cycle
Light (primary)
Long day breeders
Spring, Summer, Fall
Environment
Latitude
Weather
Housing
Stallion Exposure (induce sooner)
Nutrition
Good BCS (heavier)
Increasing plane of nutrition
Grass
Age, Breed
Young
Treatment options to bring horses out of anestrus
Expose mare to lights
16hr light : 8 hr dark
Doesn’t need to be gradual
Still go through transition
60-70 days before desired breed date
Adequate light needed
Portable digital light meter
100 lux
100-200 W
12 x 12 stall
*Adjust environment/food intake
Follicular aspiration
Hormones/analogs
-A variety have been tried with Varying success
–Better in late transition
Better if used in combination
Lights
Nutrition
Hormone/ analogs work best in the mare when…
They are in late transition
Do not work well to bring out of anestrus
Estrus cycle in mares
Estrus: 3-9 days
Diestrus: 14-16 days
Day 0- ovulation
-CL development, Progesterone production
–Beginning of diestrus
Diestrus in the mare
14-16 days (little variation)
Corpus Luteum
Not- Palpable (Ovaries are inside out compared to other species) (Visible via U/S)
Progesterone
Uterine tone- firm
Cervical tone- firm
No uterine edema (little color difference on US)
Behavior
Passive to aggressive response
When teased to a stallion:
-Obvious hostility, ears back, striking, biting, squealing
In diestrus the uterine and cervix tone in the mare is…
Firm (1 on scale)
No edema present
If a mare is in diestrus and teased with a stallion they will be…
Obvious hostility, ears back, striking, biting, squealing
Diestrus in the mare ends with…
Luteolysis
Prostaglandin F2 alpha from the myometrium of the uterus- SYSTEMIC release in the mare
Released when mare is not pregnant
FSH levels during Diestrus in the mare
Follicular recruitment
Most mares have 1 follicular wave
Some mares have 2
Mid to end diestrus will peak
Prepare for next estrous cycle
FSH levels in the mare peak during which part of the estrus cycle?
Mid to end of diestrus
Prepare for the next estrus
Estrus in the mare
3-9 days (variable)
Shorter in late season (increase chances of getting pregnant as season is ending)
Follicular development
Dominant follicle(s) emerges
-Estrogen increases
-Positive feedback LH
-Negative feedback FSH
-Inhibin
-Negative feedback FSH
LH rises
-Peaks after ovulation
-Progesterone low (no CL)
