Therio - Mare Comparative Anatomy & Physio 1

drraythe's version from 2017-10-09 15:53

Anatomy/ Physiology

Question Answer
How does the shape of the uterus differ from a cows?More "T" shaped
How is a horses' ovary different?Theyre inside out (cortex on inside & medulla on outside) so have an ovulation fossa
What kind of cervix do horses have?Muscular cervix (not fibrous) so responsive to hormones (if estrogen soft & open so hard to feel..)
What are you able to palpate on a horse ovary?Bc theyre inside out, can only feel follicles on horses & cant feel CL
PROGESTERONE: Closed, Firm on palpation
PROGESTERONE: Firm – can palpate structure
What type of cycle do horses have?Seasonally polyestrous (LONG DAY breeders) estrus cycle will repeat until season is over
Explain how being a long-day breeder worksTheir cycle is controlled by the PHOTOPERIOD which affects MELATONIN production
So, there are photoreceptors on the retina which register the light. Melatonin is secreted at NIGHT so when there are LONGer days (more light) there is LESS melatonin. Melatonin inhibits GnRH secretion, so less melatonin → less inhibition → MORE GnRH secretion, mare starts cycling more.
Will MORE melatonin turn the horses cycle on or off?MORE MELATONIN = SWITCH OFF (remember melatonin secreted at night & horses are long day breeders so more night more melatonin not cycling)
What 2 endogenous chemicals are responsible for controlling the horses' cycle?Melatonin & Prolactin
What stimulates & what inhibits prolactin?Stimulated by Seratonin, inhibited by dopamine (inhibition/suppression = prolonged gestation & agalactia)
3 factors which affect the cycle of the horse?(1) Ambient temp (colder = wont cycle)
(2) Body condition/health (skinny = wont cycle) (need Leptin which is stored in fat)
(3) Nutrition
From around which mos is the mare's natural breeding season?From ~April-May to Sept-Oct
From around which mos is the mare's 2 transition periods?Fall transition in Oct-Nov & spring transition in Mar-Apr
From around which months is the mare's anestrus/anovulatory season?Dec-Feb
When is the "birthday" of all thoroughbred foals in the northern hemisphere?JAN 1st
Average length of estrOus cycle?About 21d
About how long is estrus?6d
About how long is diestrus?15d
When in the cycle does ovulation occur in mares?Last 24-48h of estrus
What type of ovulation do mares have?Spontaneous
Which parts of the estrOus cycle do mares not have?No proestrus or metestrus
3 main ways of monitoring the estrus cycle?Teasing scores
Rectal palpation
Follicles grow & regress throughout cycle...what is required for them to progress? Ovulate?Progression is czd by FSH
Ovulation is czd by LH
How many follicular waves are there per cycle?1-2
At what size of follicle can it be ready to ovulate?Ovulate from 3.5-6 cm in size! (vs cows which is like 18-20mm)
Can a horse have mult ovulations?Can get multiple ovulations - often repeatable & hereditary (Thoroughbreds twin a lot)
Who is prone to mult ovulations?Thoroughbreds (T is for Twins!!)
What do the hormones look like when going through the cycle? (pic)
What is a teasing score of 0 like?Not interested; kicks, squeals (Headache)
What is a teasing score of 1 like?Passive (Maybe... need flowers, chocolate & wine)
What is a teasing score of 2 like?Interested; ears pricked, winks (Need a little bit of effort...)
What is a teasing score of 3 like?Very interested; winking + intermittent urination (Keen)
What is a teasing score of 4 like?Winking, squatting, constant urination (Ready for the sex....)
What is a "foal heat" ?Go into estrus 9d after given birth... usually not fertile heat
What does a teasing score sheet look like? (pic)
What is the uterus, cervix, & ovary like during estrus? (Rectal palpation)Estrus = under influence of estrogen, so:
UTERUS: Low tone (doughy feeling due to edema)
CERVIX: Low tone & OPEN.
OVARY: You can palpate the follicles (v large- 3.5-6cm size), feel like large blisters, & have an ovulation fossa bc inside out so cant really feel much else
What’s the gross looking pink thing? The big pink thing is a follicle in the ovulation fossa
How does an ovary look like on U/S when in estrus?Can see a dominant follicle
How can you measure the size of a follicle on U/S?You take the AVERAGE of the perpendicular distances (average the length & height)
On U/S uterine edema is measured on a scale of...0-3, where 0 is no edema & 3 is max edema
What does uterine edema look like on a U/S?“Wagon wheel” or “Orange Segments"
What part of the uterus is actually edema-ing?Edema is w/in the ENDOMETRIUM
What does it mean if there is intraluminal uterine edema? What does it look like? (How can you Tx?)This is PATHOLOGICAL. BAD. (give Oxytocin to evac fluid).
How long is the CL refractory (not responsive) to PGF2α after ovulation?CL refractory to PGF2 until D5 post-ovulation
What is the uterus, cervix & ovary like during diestrus?Diestrus = Under influence of progesterone, so:
UTERUS: High tone
OVARY: You can't palpate the CL (but it's there)
What will you see on U/S on a horse in EARLY diestrus?See Corpus hemorrhagicum (looks like dense cobwebs) (remember, refractory to PGF2 for +/- 5d after ovulation)
What will you see on U/S on a horse ovary in diestrus (not early diestrus)See CL
What does vernal mean?During spring
During spring, there is transitional estrus...explain what is going on to cz this (why isn't it just full-blown estrus?)During spring there is starting to be inc daylight. Inc daylight → dec melatonin → inc GnRH → inc FSH → initiates follicular development (follicles then produce estrogen). However, during this time LH secretion is LOW (not really any "stores" built up/ need gene switched on) so dont really ovulate
How does spring transitional estrus differ from regular estrus from observation (& why?)Although there is follicular development, the follicles don't ovulate (not enough LH) Therefore, get prolonged "heat" signs + erratic "interestrous intervals" during spring w/ no ovulation - "Spring heat" or "Transitional heat". This is probably bc require a threshold of estrogen in order to cz LH surge & ovulation
How does the ovary feel during spring transition on rectal palpation?Feels like "bunch of grapes" bc of the mult follicles
How does the ovary appear on U/S during spring transition?Multiple follicles, None of ovulatory size (ie. 3.5-6cm) (bc of how it looks DDx is granulosa cell tumor)
What is happening to the ovary during Autumn transition?Ovary in the process of "switching off"
How does the ovary appear on U/S during autumn transition?See multiple anovulatory follicles (get all the way to 6 cm but dont ovulate & then fill w/ blood)
When during the yr does anestrus occur?Winter (short days!)
How does winter trigger anestrus & how is the ovary effected?Dec daylight → Inc melatonin → Dec GnRH (melatonin has an inhibitory effect) → Dec FSH + LH (dec mRNA & gene turned off)- → fxnl ovarian atrophy
How do ovaries feel on rectal palpation during anestrus?Ovaries small, smooth & inactive
What are estrogen (E2) & progesterone (P4) levels like during anestrus?Undetectable
What is the horse's hair coat like during winter, & why?Dry winter coat (no E2 aka estrogen)
What stage of her cycle was she in during the end of March/beginning of April? Spring transitional estrus

Controlling the estrous cycle- INDUCTION of ESTRUS

Question Answer
In order to use photoperiod to control the estrus cycle, you must provide light for how long each day, from what time calendar-wise?Fixed photo period (14.5-16h daylight) from 15 Nov - 1st Dec (Northern Hemisphere) until Mid-April (light must be bright enough for you to read a newspaper w/)
If you don't feel like doing the 14.5-16hr of daylight for roughly 60d (from 15nov to 1st dec), what other thing can you do to the photoperiod?1h light exactly 9.5h after sunset (admin)
What is the "lag period" of photoperiod manipulation? (Ie how long it starts to work after you start it)Lag period of 60-75d
No matter how much light you give the horses, what 2 things must you do in order for photoperiod manipulation to work?Good quality food + keep warm
(must be good BW & warm to go into estrus)
How bright must the light be when you are doing artificial photoperiod Tx?Light intensity: If you can read a newspaper in all areas where the mares are housed...Basically equivalent to 100W
If you don't wanna have super bright lights on all the time, someone figured out what kinda light works w/ the melatonin secretion?Recently discovered that low intensity blue light inhibits melatonin secretion-- so they developed a mask that lights up 1 eye w/ low intensity blue light
Can you use hormonal Txs to start estrus during anestrus?NOT ALONE - only when added to the end of the lighting regimen can advance the 1st ovulation
WHEN can you use hormones to advance 1st ovulation? (What follicle requirements are there?)Hormonal Tx added to the end of the lighting regimen can advance the 1st ovulation... Need 25-35mm follicles present before starting Tx.
Which drugs can you use (in supplement to photoperiod manipulation) to induce estrus? (6 choices) [*remember follicles must be at least 25-35mm](1) Progesterone (P4) alone
(2) P4 + Estradiol
(3) PGF
(4) hCG
(5) GnRH agonists (Deslorelin, gonadorelin ("Fertagyl"))
(6) Dopamine antagonists (Sulpiride, Domperidone) (bc dopamine antagonizes prolactin)
PROGESTERONE alone is usually given during what time of yr to horses? For how long? WHY is it given?Given in late spring transition for 14-18d in order to Suppress estrus – allows follicles to grow, therefore when you stop Tx, should come into estrus. (Can give IM or orally)
So you are giving progesterone for 14-18d to suppress estrus to allow the follicles to grow. You can give PGF on the last day of this Tx...why?In case there is a CL dont want any endogenous progesterone preventing the start of estrus when the Tx is stopped (this is also the case for why you can do it at the end of the 10d regimen of progesterone+estradiol)
What time of yr do you give Progesterone + estradiol? For how long? WHY is it given?Given in late spring transition for 10d. This is given bc it Suppresses estrus – allows follicles to grow, therefore when you stop Tx, should come into estrus
Why give progesterone & estradiol at the same time?1 suppresses LH & the other FSH
WHEN do we give hCG or GnRH agonists (Deslorelin) (during time of yr)? What must the follicle be like for this Tx? WHY do we give these drugs?Given in late spring transition when follicle >35mm, & we give bc Induces ovulation (hCG) or hastens (quickens) follicular growth & ovulation (GnRH) (given as 1 injxn)
Why do we give Dopamine antagonists to induce estrus?(Ex of drugs is Sulpiride, Domperidone) Dopamine is suppressive on prolactin (& prolactin czs estrus) antagonizing dopamine → inc prolactin → estrus
So these dopamine antagonists compete w/ dopamine, therefore removes neg-feedback on prolactin- → Induce follicular growth during transition (EXACT MECHANISM UNKNOWN!)
When exactly do you want to give the dopamine antagonists? (Relative to length of other Tx, & time of yr)10-35d after 2wks of Light Tx in January

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