When does puberty occur in a filly? When are mares in oestrous? When is the natural breeding season for horses in the southern hemisphere?
* 2nd spring of a filly's life
* Mares are seasonally polyoestrous- 21 days- anoestrous period every year
* October to March is the natural season in the Southern Hemisphere
How long is the average oestrous cycle for a mare? How long is the mean duration of dioestrus?
Duration of dioestrus: 15 days
When do you do a clitoral swab, what are you mostly testing for?
Pseudomonas aeruginosa, Klebsiella pneumoniae, Taylorella equigentitalis (all causing contagious equine metritis (CEM)
When should you take endometrial samples in horses? Why?
* because the uterus should be free of pathogens in dioestrous
* Exudates are easier to detect
* oedema should not be present (problem in oestrous: inflammatory or oestral oedema)
* Biopsy evaluation will be more meaningful with no oestral oedema or inflammatory cells
BUT DAY 5 or after... because the CL is responsive to PG2alpha so that you can clear out the uterus
Beware: uterus is very susceptible to infection in dioestrous
What does an endometrial sample tell us?
* Only comment on breeding soundness, not on fertility
* Helps describe mares chance of falling pregnant
* Determine if tubular or endocrine disorder present and if it can be treated
How might you induce oestrus earlier in season in a mare? How long is required until well into transition? How many hours per day?
* Artificial/ supplemental light
* Requires minimum of 60 days of stimulation (16 hours per day) until well into transition- may need 90 days to result in ovulation-- maintain under lights until diagnosed safely in foal
( same effect shown with 1 hour of light exactly 9.5 hours after sunset)
How do you suppress oestrous in a mare?
* Progesterone e.g. oral Regumate, long acting injectable
* GnRH vaccines (Equity); follicular activity may not return
* Marble in uterus (only 50% successful)
* Infusion of plant oils in uterus in dioestrous (delays luteolysis in 92% when administered at day 10)
How can you synch oestrous?
* Planned matings
* AI and embryo transfer
* Silent oestrous
* Persistent CL--> allows advanced planning
* If mare is in luteal phase, PGF2alpha- luteolysis after single dose-- standing oestrus after 3 to 6 days-- may take longer to come into heat if small/ atretic follicles, (Granulosa (theca) cell tumour), if they are in dioestrous but less than 5 days ago won't work, if they aren't in luteal phase (anoestrous, silent oestrous, transitional oestrus, >35 days pregnant)
* Combined oestrogen-progesterone treatment
How does combined oestrogen- progesterone treatment?
IM injection of 150 mg progesterone and 10 mg of oestradiol in oil for 10 days, PGF2alpha on day 10, progesterone stimulates dioestrous- small amount of oestradiol suppress growth of small follicles... at time of withdrawal all mares start with new follicular wave.... At start of treatment-- mares in heat: ovulate in first few days of treatment, mares in early mid-dioestrous will have responsive CL, mares in late dioestrous: will have undergone spontaneous luteolysis
Pros and Cons of PGF2alph, P& E, Regumate for synchronization of oestrous in mares?
Why would you induce ovulation in a mare?
* Accurately time OV in mares scheduled for breeding, AI
* Part of synchronization program
* Means of interrupting transitional oestrous
* Treatment of anovulation (extremely rare condition)
* Induced OV assumed to be as fertile as spontaneous one
How do you induce ovulation in a mare?
* Human chorionic gonadotropin (hCG): LH like function, IV injection of 1500 IU, results in antibody production (probably no interference with action), if given with a 35 mm follicle and some oedema 85% of mares ovulate between 36 and 42 hours--- Might not work in transition when lack of LH receptors
* GnRH analogues- deslorelin (ovuplant or injectable)- ovulation between 42 and 48 hours if given as soon as largest follicle is 30 mm, implant should be removed to prevent downregulation
How should you time your ovulation induction?
* Trade off between sperm longevity vs. uterine clearance of bacteria, debris introduced by AI
* Ideally to be done at a time of insemination/breeding (except frozen semen!)
* If semen stored more than 30 hours, induce OV 24 hours before AI
When should you re-examine the mare after OV induction?
* 48 hours later, if induced early enough
* 80% of mares follow the book
* Rest might not ovulate at all that cycle
* in that case discuss if more semen is to be invested (wasted)
What are tests that determine time for breeding a mare?
* Teasing, rectal exam: palpation and ultrasound, (vaginal exam)
How do you conduct teasing with a mare?
* Most important management tool for breeders (especially TB studs)
* Preferably done by same person every day
* Keep records
* Mares must be teased regularly (ideally daily) from 3 days post-partum until 60 days pregnant
When is the mare ready to be bred?
* Ovulatory follicle: usually +/- 5 mm of same size each cycle (individual differences are large)
* Increasing oedema
* Cervix relaxes in oestrus, open in ovulation, then it closes
Problems with natural breeding
* Stallions can only breed limited number of mares, mare and stallion same location, risk of disease, injuries, difficult to assess semen quality (dismount sample)
Advantages of AI over natural service
* more mares can be bred to a single stallion
* mare and stallion do not have to be in the same location
* limiting transmission of venereal disease
* in case of incompatibility (size, temperament, physical disability) breeding still possible
*minimum contamination breeding technique possible
* semen quality can be monitored
What is the avg AI dose in equine? How do you count? How do you assess motility?
500 million progessively motile sperm, haemocytometre, motility assessment (heated phase contrast microscope) done at 37C
Advantages and Disadvantages of raw semen?
* Minimize injuries
* Assess semen quality
* Breed multiple mares from same ejaculate
* dirtiest of all AI methods
* Risk of iatrogenic infection especially when done in early or late oestrous
* AI does not dilate cervix as stallion's penis would do (clearing contaminants)
How do you AI with raw semen?
* Collect, remove gel fraction, assess motility, deposit desired dose into uterus within 30 minutes
Fresh extended semen
* minimizes contamination for mares suscpetible to endometritis
* 1 part semen: 4 parts extender
* extend sample to a concentration of 25-50 million/ ml
* should be used within 3 hours at room temp
Cool extended semen
* Cooled extended semen: 75% first service conception
* not all stallions can have semen successfully shipped
* Stallion collection schedule: MWF or TTS
* Cooled to 5C
* Cooling rate critical 1C/ 3 minutes (commercially available shipping containser to cool at ideal rate)
Set time AI with ovulation induction schedule example
* Advantages: semen available without regard to stallion's racing/show schedule, can be shipped worldwide, even decreased stallion's semen can be used for breeding
* Disadvantages: 12 hours prior to 6 hours after ovulation; advanced planning, ability of stallion's sperm to survive freezing process, management more expensive* Management more expensive* Management more expensive
* Liquid nitrogen or vapor
* avg 30-35% success/ cycle-- increase success if mare is of ideal breeding health-- try on 3 successive cycles, if not by 3rd cycle switch to fresh or chilled
With AI, what should you do if the mare does not ovulate when expected?
* Owner makes the decision if that cycle has to be skipped or mare must be scanned every 6 hours to be inseminated again once ovulation is detected
* Mare should not be AI'd again until at least 18 hours after 1st AI (inflammatory uterine reaction)
Considerations with breeding a maiden mare
* Transrectal palpation, ultrasound
* If normal: vaginal check for hymen
* Uterine cylture: "true" maiden has a sterile uterus at start of season and can't infect the stallion unless/ until bred to infected horse and/or bred ith poor technique--> good candidate for all methods
Considerations with breeding a barren mare?
Bred in prior season(s); not currently pregnant
* Age > 13-14 years??
* Vulvar conformation?
Quick review on events after sperm deposited (where?) in equine
* Sperm deposited into uterus
* fertilization in ampulla of oviduct
* transport of conceptus into uterus (5 to 6 days after OV)
* Unfertilized ova remain in oviduct
* conceptus signals its presence by traversing whole uterus
* prostaglandin inhibitory factor produced (PIF)
* mobility phase until D 16
* then conceptus "get stuck" at the base of uterine horn