REPRODUCTION - Equine Breeding Management Flashcards
What is the mares ovulatory cycle?
Mares and seasonal polyoestrus long day breeders, meaning their oestrous cycles are during the summer months and they are anoestrus during the winter months. Each oestrous cycle is 21 days long, with a 7 day oestrus and a 14 day dioestrus. The first oestrus will usually start early April and continue until September
Be aware some mares will continue to cycle during winter
Which hormonal changes occur during the mare oestrous cycle?
The mare is brought into oestrus due to rising levels of oestrogen produced by the dominant follicle, medicated by LH. This rapid oestrogen production in the absence of progesterone induces the surge of gonadotropin releasing hormone (GnRH) which stimulates ovulation. The mare ovalutes 1-2 days before the end of oestrus (The LH surge occurs after oestrus in the mare), meaning oestrogen levels will decrease and in the absence of oestrogen, luteinisation can proceed and progesterone production can begin (which will have a negative feedback effect on LH). Mares have an FSH rise in late oestrus which triggers cohort emergence immediately after ovulation, where a dominant follicle can be selected. Mares also have a rise in FSH midcycle, which triggers cohort emergence and a dominant follicle can be selected and trigger ovulation
What are the signs of oestrus in the mare?
Raised tail
Tail moved to the side
Spraying urine
‘Winking’ (clitoral eversion)
‘Cartwheel’ appearance of the uterine horn on ultrasound (due to thickening and oedema)
What is ‘foal heat’?
Mares resume ovulation during lactation, and thus ‘foal heat’ is the first oestrous cycle after foaling, and the mares ovulate 7 - 10 days post party
Why is there reduced fertility during ‘foal heat’?
There is reduced ferility and conception rate and there is reduced uterine motility and oncomplete uterine involution
What is a northern hemisphere ‘foal Birthday’?
The northern hemisphere foal birthday is the 1st of January, meaning that no matter when during the year a foal is born, their official birthday is the 1st of January
Why is it beneficial to have foals born as close to the ‘foal birthday’ as possible?
Foals born earlier in the year often have an advantage in physical maturity when competing in age-restricted races
When do the thoroughbred breeding shed open?
The thoroughbred breeding sheds open on the 15th February
What can be done to try and identify the stage of the oestrous cycle in the mare?
Teasing
Rectal palpation
Transrectal ultrasound
Vaginal speculum examination
Breeding records
What is teasing?
Teasing is assessing the behaviour of the mare when she is presented with a stallion. If the mare is in oestrus, she will be receptive to the stallion
Which hormone mediates teasing behaviours in the mare?
Oestrogen and a lack of progesterone are key for the receptive teasing behaviours of the mare
Lack of progesterone is very important
What are the con of using teasing behaviours to assess the stage of the oestrous cycle in mares?
Maiden mares (never been mates before) may not exhibit oestrus behaviours when presented with a stallion as they can be unsure, and mares with foals at foot may not exhibit oestrus behaviours due to fear and uncertainty
How can you assess the stage of the oestrous cycle via rectal palpation?
Not as accurate as teasing
You can assess for follicular development, the cervix and the uterus via rectal palpation. Mares in oestrus will have soft uterine tone, a relaxed open cervix and you can palpate follicles. Mares in dioestrus will have prominent uterine tone and a closed cervix (you can’t palpate corpus lutea in mares)
What information can be provided by transrectal ultrasound?
Follicular size, shape and echogenicity
Endometrial oedema
Identify corpus lutea
Pathological changes
How does follicular size and shape change approaching ovulation?
Follicles will get larger, less rounded and the follicular walls will thicken leading up to ovulation. Mares typically ovulate follicles 4 - 5cm large
How does endometrial oedema vary during different stages of the oestrous cycle?
During oestrus, endometrial oedema will increase until is reaches a maximum and begins to reduce just prior to or after ovulation. There is no endometrial oedema during dioestrus or anoestrus
How can you distinguish endometrial oedema from pathological fluid accumulation?
Endometrial oedema is anechoic, if the fluid is more turbid/echogenic, it is cellular and more likely to be pathological
What is physometra?
Physometra is the accumulation of air in the uterus
How can a vaginal speculum exam be used to determine the stage of the oestrous cycle in the mare?
Vaginal speculum exam can be used to examine the cervx which will have a varying appearance during different stages of the oestrous cycle
How does the cervix appear during oestrus?
The cervix is more relaxed and sits on the vaginal floor, with a ‘wilted rose’ appearance
How does the cervix appear during dioestrus and anoestrus?
The cervis is tense and ‘pulled up’ in appearance with a visible frenulum
What can be done to manipulate the mare’s oestrous cycle?
Shorten the lifespan of the corpus luteum (short-cycling)
Ovulation induction (programming)
Oestrus suppression
Oestrus synchronisation
Manipulate spring transition
How can you shorten the lifespan of the corpus luteum?
Prostaglandin administration
When is it appropriate to administer a prostaglandin injection to ‘short cycle’ a mare?
You can administer prostaglandin to ‘short cycle’ a mare when the corpus luteum is at least 5 days old to lyse the corpus luteum
When will the mare go into oestrus following prostaglandin administration?
The mare will typically go into oestrus 2 - 4 days following prostaglandin administration, however, time of ovulation can very between 5 - 12 days after prostaglandin administration
What are the potential side effects of prostaglandin adminstration?
Sweating
Diarrhoea
Colic
Which key factors should you be aware of when carrying out ovulation induction in mares?
Drugs can be administered to induce ovulation in mares, however this will only work if there is a dominant follicle present, so these drugs realistically only bring ovulation forward by a few days. However, the predictability of the effects of these drugs can be very useful in terms of artificial insemination
Which drugs can be used to induce ovulation in the mare?
Human chorionic gonadotrophin (GnRH)
Deslorelin (synthetic GnRH)
How does human chorionic gonadotrophin and deslorelin induce ovulation in mares?
Human chorionic gonadotrophin and deslorelin have an LH like effect on the follicle to induce ovulation
When do mares typically ovulate following administration of human chorionic gonadotrophin?
36 hours post administration
When do mares typically ovulate following administration of deslorelin?
40 - 42 hours post administration
How can you synchronise oestrus in mares?
Progestrogen and oestrodiol injections for 10 days
Prostaglandin (2 injections 14 days apart)
Synchronising oestrus in mares is very challenging
What is the indicator for oestrus suppression in the mare?
Oestrus suppression is indicated to prevent unwanted oestrus behaviours
What should you always do prior to carrying out oestrus suppression in mares?
Detailed history
Clinical examination
Reproductive examination
Why is it so important to get a detailed history before beginning oestrus suppression in the mare?
Take a detailed history to try and determine why owners want oestrus suppression and to determine if any unwanted behaviours are definitely associated with oestrus. A 30 day treatment trial can be used whilst keeping a behaviour diary to determine if the behaviours are due to oestrus
What can be used to suppress oestrus in the mare?
Altrenogest
Intrauterine marble
Upod
Ovariectomy
What is altrenogest?
Altrenogest is a synthetic progesterone agonist which suppresses oestrus in mares
What are the benefits of oral altrenogest over injectable altrenogest?
Oral altrenogest is easier and cheaper to do, injectable altrenogest is more expenise, requires a veterinarian for administration and mares can get injection site reactions
How does an intrauterine marble suppress oestrus in mares?
An intrauterine marble can make mares think they are pregnant and thus their body will produce natural progesterone and suppress oestrus
What is the main disadvantage of an intrauterine marble?
Some mares will spontaneously expel the marble and go back into oestrus
What is a Upod?
A Upod is an intrauterine device made up of three plastic coated magnets which have the same affect as the intrauterine marble, however are less likely to be spontaneously expelled
What is spring transition?
The spring transition is a period of anovulatory receptivity where mares can exhbit erratic oestrus behaviour and appear as if they are standing to mate however, there is no associated ovulation of a dominant follicle. This can be very frustrating for breeders, so it can be best to advise to wait until there is evidence of ovulation (corpus luteum on ultrasound) before beginning breeding
How can you manipulate the spring transition?
You can carry out photostimulation through stabling the mare and turning the barn lights on so there is 14 - 16 hours of light per day to help stimulate ovulation, this has to be done for 8-10 days prior to when breeding commences. If you want to keep the mare out on pasture, you can do this using the equilume head mask which produces blue light
What are the different methods available for breeding mares?
Natural cover
Artificial insemination (fresh, fresh chilled, or frozen)
(T/F) You cannot use artificial insemination in racing thoroughbreds
TRUE. If you want to register the foal with Jockey club you cannot use artificial insemination, they must be produced by natural mating
What is pasture breeding?
Pasture breeding is where a stallion is turned out with a band of up to 15 - 20 mares for 2 to 3 months during the breeding season
What is hand mating?
Breeding in hand is when a stallion and mare are handled in such a way that they are both restrained, and the act of breeding is orchestrated in a controlled environment
Which form of semen has the best conception rates in terms of artificial insemination?
Fresh semen
When should you order fresh cooled semen?
You should order fresh, cooled semen when the dominant follicle has reached 30 - 35mm
How long is fresh cooled sperm viable once it has been inseminated?
Fresh cooled sperm is viable for approximately 24 - 48 hours after insemination, so be aware if the mare hasn’t ovulated before 48 hours after insemination, you may need to order in more semen
How do you thaw frozen semen?
Remove the semen straws from the liquid nitrogen and thaw in room temperature water. Inseminate as soon as the semen is at room temperature
Frozen semen can be VERY expensive
How long is sperm from frozen semen viable once it has been thawed?
12 - 24 hours
What is a post ovulation artificial insemination (AI) protocol in mares?
- Examine and scan the mare daily until a 30-35mm dominant follicle is present
- Administer an ovulating agent to stimulate ovulation
- Ultrasound scan the mare to monitor for ovulation ever 6-8 hour
- Inseminate within 6 hours of ovulation (as this is how long the oocyte will remain viable after ovulation)
This labour intensive but useful for single dose frozen semen
What is a timed artificial insemination (AI) protocol in mares?
- Examine and scan the mare daily until a 30-35mm dominant follicle is present
- Administer an ovulating agent to stimulate ovulation
- Inseminate with one dose at 24 hours post-ovulating agent
- Inseminate with a second dose at 40 hours post ovulating agent
What is a potential complication following breeding?
The semen can cause a reaction and infection in the mare’s reproductive tract
What should be done 24 hours post breeding?
Check to make sure the mare has definitely ovulated (scan to assess for development of a corpus luteum)
Check for any uterine fluid or debris that may need to be evacuated
Why is it important to evacuate any uterine fluid or debris 24 hours post breeding?
It is important to evacuate any uterine fluid or debris post breeding as if conception has been successful, the embryo will be travelling into the uterus within 6 days post conception so the uterine environment should be optimal
How can you evacuate uterine fluid?
Uterine lavage
Oxytocin
