Equine Breeding Programs Flashcards
What is a stallions book?
list of mares that will be bred to him in a given year
What is a cover
when a stallion breeds a mare naturally
what is a mount/phantom/dummy
fake mare that allows us to collect semen for AI when stallion mounts it
what is an artificial vagina
what we use to collect semen from a stallion
what are the four methods of mare breeding
-natural service
-on farm AI
-shipped fresh chilled AI
-frozen semen AI
what is the only approved method of breeding in thoroughbreds to obtain a registered foal?
Natural cover
advantages of natural cover breedings (5)
-Minimal equipment expenses (no lab etc)
-Obvious when mare is in heat
-No knowledge of semen handling required
-No semen shipments lost
-High conception rate
disadvantages of natural cover breedings (4)
-Risks of injury to horses and handlers
-One mare bred per ejaculation
-Mares must travel to stallion (often with new foal)
~assoc. risks and costs
-Some mares will not accept a stallion even when in estrus
What needs to be done in natural cover programs to assure no disease transmission occurs?
-Pre-breeding culture swabs
-Clean breeding practices
advantages of AI (5)
-Mare & foal stay at home
-Efficient
-Many mares can be bred with a single collection
-Fresh-chilled semen lasts about 48+ hours when diluted with semen extender
-Frozen semen - stallion continues performance career without interruption
disadvantages of AI (2)
-Increased expenses
◦ Laboratory costs
◦ Semen shipping cost
◦ Veterinary costs of mare management
-Considerable knowledge in semen handling
advantages of frozen semen (4)
-Permanent storage
-Semen available anytime
-Stallions continue performing
-Improved genetics – use of stallions around the world
disadvantages of frozen semen (1)
-Higher costs
◦ Semen collection, freezing, storage, transport
◦ Very intensive mare monitoring required
◦ Requires specialized equipment and expertise
characteristics of anovulatory season (dec-feb)
◦ Variable behavior
~Usually uninterested in stallion – “meh”
◦ Small ovaries, small follicles <10 mm
◦ Flaccid uterus, no edema
◦ Cervix – pale, tight or relaxed
levels of GnRH, FSH, LH, estrogen and P4 in winter anestrus
-decreased GnRH and FSH
-no LH, estrogen or P4
What environmental factor triggers the resurgence of ovarian activity?
Increased daylength
What hormone is released in response to increased daylength?
GnRH
What happens to FSH levels during the resurgence of ovarian activity?
it increases
What is notable about the follicles during spring transition?
Follicles start to grow but do not produce much estrogen
What is the status of LH during the resurgence of ovarian activity in spring transition?
There is low bioactive LH and no LH receptors, so ovulation does not occur
Describe the characteristics of the ovaries during the spring transition
The ovaries are large with multiple follicles
What changes occur in the uterus during spring transition?
The uterus is flaccid with variable edema
What is the typical state of the cervix during the resurgence of ovarian activity?
The cervix is usually relaxed and may appear pale to pink
when does ovulatory season occur
may to september
what signals the ovulatory season
the first ovulation of the year….. cyling then occurs every 21d after that
What are some characteristics of estrus (behaviour and what we see on ultrasound)
-Teasing – signs of estrus – receptive, winking of vulva, posturing, urination
-Follicles growing on ovaries
-Flaccid uterus, open, pink cervix on floor of vagina
-Uterine edema
what are the characteristics of diestrus (behaviour and ultrasound)
-Teasing – aggressively refuses
stallion
◦ Kicks, bites, pins ears, squeals
-Corpus luteum on ovary– high
progesterone
-Toned uterus
-No edema
what hormone is very high during diestrus
progesterone
when does the fall transition occur and why
october to november
due to decreasing daylength
what are autumn follicles
they are anovulatory follicles… or failed ovulations
what happens to LH and GnRH in the mare during the fall transition
decreased LH production (gene turns off)
decreased GnRH
what happens to the ovary during fall transition
decreased P4 levels, luteal failure, shortened luteal phase
what are some reasons to manipulate a mares cycle? (5)
-Out of season breeding
-Synchronize a group of mares for breeding
-Control timing of estrus (eg. For shipping semen)
-Induce ovulation (eg. Once semen arrives)
-Control unwanted estrous behavior (performance mares)
how do you implement standard method for photoperiod manipulation in mares?
-14.5 - 16 hours of light total
-Add light to end of day
what is the idea behind the standard method for photoperiod manipulation in mares?
-Idea is to stimulate earlier spring transition period
-Resume cycling 60-70 days after starting
-Start between Nov 15 – Dec 5 for Feb breeding
-Continue until days are 14 hrs long
what is the pulse lighting method of photoperiod manipulation in mares?
-Photosensitive period 8–10 hours after onset of darkness
-Usually 2 am – 4 am
-1.5-2 hours of “lights on”
-Must be high intensity light (100 Watt)
-Start between Nov 15-Dec 5 and continue until days are 14 hrs
-Saves energy!
Why won’t PGF2α be effective in treating anestrus mares?
PGF2α is ineffective because there are no active CL (corpora lutea) to regress, as anestrus mares lack sufficient ovarian activity.
Why won’t GnRH or hCG work in anestrus mares?
GnRH or hCG are ineffective because there is insufficient ovarian responsiveness and low levels of LH receptors, leading to no ovulation
What are dopamine antagonists used in treating anestrus mares?
Sulpiride or domperidone.
How do dopamine antagonists affect prolactin levels?
They increase prolactin levels, which can enhance follicular activity.
Are dopamine antagonists effective on their own for treating anestrus mares?
No, they are not very effective on their own and may need to be used in conjunction with other treatments
what is the frustrating part of spring transition for vets?
there is growth of dominant sized follicles that just fail to ovulate
what is used to induce first ovulation of the year
P4
combination of domperidone and estrogen
GnRH or hCG
What is the purpose of P4 therapy in mares
Mimics a functional CL – inhibits LH release; little effect
on FSH
Progesterone therapy; requirements
-Regumate = Synthetic progestin (Altrenogest)
-Give orally for 10-14 days
-Must have follicles >25 mm (mid transition)
-Give PGF2a on last day (just in case she ovulated during treatment)
Process for combination therapy in transitional mares
-One Initial 75 mg Estradiol Cypionate (ECP) injection I.M.
and 500 mg domperidone orally daily for 7 - 14 days
(addition of estrogen enhances LH receptors on the growing follicles)
are CIDRs used in north america? why?
No, results in nasty vaginitis
what is the most common way of prolonging the luteal phase
oral altrenogest (regumate)
why is hCG used in mares?
to induce ovulation
when do you give hCG to the mare?
Give to a mare in estrus with:
-Follicle > 35 mm and Strong uterine edema
when will a mare ovulate after you give hCG
-Most will ovulate within 48 hours
-Most at 36 hours after administration (85.1% by then)
what drug do you switch to if you have used hCG multiple times per breeding season?
gNRH
what is the age effect of hCG
repeated exposures = less effective
what is the effectiveness of GnRH
Over 95% of mares ovulate within 48 hours after injection when given in estrus with dominant follicle > 33 mm
is there any concern of reduced efficacy over time for GnRH
no
what happens to the follicles as ovulation approaches
softer, irregular in shape, larger
how much does a follicle grow per day on average
3-6mm per day
details about combination programs (P and E) for mares
-Combines daily progesterone and estradiol injections
-Estradiol suppresses FSH – control of follicle waves
-10 day treatment
-PGF2a on last day
-In estrus 7-9 days after last injections
-Predictable ovulation day 20-21 of program
what does the size of the follicle at ovulation depend on?
breed and mare history
