Estrous Cycle
describe the 3 phases of the estrous cycle
estrus: fertile period
diestrus: infertile period
Anestrus: nothing happening
When is the length of estrus more variable?
At the beginning of breeding season
What hormone precedes ovulation?
Luteinizing hormone
What are 5 reasons that we want to manipulate our mare's cycle?
- decrease time between cycles
- breed registry rules
- schedule with a stallion
- optimize chance of fertilization
- behavioral reasons
What happens to LH and FSH during the transitional phases?
LH is low, FSH is increased
When is the naturally occurring breeding season?
Late April - Late Septmember
What is the transitional phase?
During spring and fall transitions mares will grow follicles but the follicles do not mature and will not ovulate
What does the follicular stimulating hormone?
stimulates follicle growth
How many hours of light a day should you use for an artifical light program?
16 hours a day
How can we hasten ovulation?
oral progestin, intra-vaginal progestin
What type of breeders are horses?
Long day seasonally polyestrus
What is the length of estrous and estrus?
Estrous: 21-24 days
Estrus: 5-7 days
What does the luteinizing hormone do?
produces estrogen, stimulates ovulation, luteinizes the follicle to create a corpus luteum
List 3 types of artificial lighting on a mare
stall lights, paddock lights, mask
What are 4 ways we manipulate the estrous cycle?
Hasten ovulation, destroy the CL, maintain the CL, superovulate
Why do mares cycle during the long days?
More light = less melatonin = more GNRH
What is ovulation?
when the oocyte is released from a mature follicle
What hormone does the CL secrete and what does it do?
Progesterone, needed to maintain pregnancy
How many weeks of a light program does it take to stimulate cyclinity and when should you start the program?
6-8 weeks. start in december
What does human chorionic gonadatropin do?
stimulates LH
What are the 5 primary organs of the estrous cycle?
pineal gland, hypothalamus, ovaries, pituitary and uterus
When does the luteal phase begin?
When a CL is formed
What happens if there is no viable embryo?
PGF2a sends signal to turn a CL into a CA
What are 3 results of light on a pregnant mare?
decrease gestational length, decrease height but not weight, decrease time to foal standing
How can we shorten diestrus?
administering PGF2a promotes the regression of the CL and mares will ovulate 5-10 days after