REPRODUCTION - Equine Breeding Management

Question 1

What is the mares ovulatory cycle?

Answer 1

Mares are 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

Question 2

Which hormonal changes occur during the mare oestrous cycle?

Answer 2

The mare is brought into oestrus due to rising levels of oestrogen produced by the dominant follicle, mediated 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. 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

Question 3

What are the signs of oestrus in the mare?

Answer 3

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)

Question 4

What is ‘foal heat’?

Answer 4

Mares resume ovulation during lactation, and thus ‘foal heat’ is the first oestrous cycle after foaling, and the mares ovulate 7 - 10 days post partum

Question 5

Why is there reduced fertility during ‘foal heat’?

Answer 5

There is reduced ferility and conception rate and there is reduced uterine motility and incomplete uterine involution

Question 6

What is a northern hemisphere ‘foal Birthday’?

Answer 6

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

Question 7

Why is it beneficial to have foals born as close to the ‘foal birthday’ as possible?

Answer 7

Foals born earlier in the year often have an advantage in physical maturity when competing in age-restricted races

Question 8

When do the thoroughbred breeding shed open?

Answer 8

The thoroughbred breeding sheds open on the 15th February

Question 9

What can be done to try and identify the stage of the oestrous cycle in the mare?

Answer 9

Teasing
Rectal palpation
Transrectal ultrasound
Vaginal speculum examination
Breeding records

Question 10

What is teasing?

Answer 10

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

Question 11

Which hormone mediates teasing behaviours in the mare?

Answer 11

Oestrogen and a lack of progesterone are key for the receptive teasing behaviours of the mare

Lack of progesterone is very important

Question 12

What are the con of using teasing behaviours to assess the stage of the oestrous cycle in mares?

Answer 12

Maiden mares (never been mated 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

Question 13

How can you assess the stage of the oestrous cycle via rectal palpation?

Not as accurate as teasing

Answer 13

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)

Question 14

What information can be provided by transrectal ultrasound?

Answer 14

Follicular size, shape and echogenicity
Endometrial oedema
Identify corpus lutea
Pathological changes

Question 15

How does follicular size and shape change approaching ovulation?

Answer 15

Follicles will get larger, less rounded and the follicular walls will thicken leading up to ovulation. Mares typically ovulate follicles 4 - 5cm large. When the mare has ovulated, you will be able to detect a corpus haemorrhagicum on ultrasound

Question 16

How does endometrial oedema vary during different stages of the oestrous cycle?

Answer 16

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

Question 17

How can you distinguish endometrial oedema from pathological fluid accumulation?

Answer 17

Endometrial oedema is anechoic, if the fluid is more turbid/echogenic, it is cellular and more likely to be pathological

Question 18

What is physometra?

Answer 18

Physometra is the accumulation of air in the uterus

Note the reverberation and 'white speckles' of gas

Question 19

How can a vaginal speculum exam be used to determine the stage of the oestrous cycle in the mare?

Answer 19

Vaginal speculum exam can be used to examine the cervx which will have a varying appearance during different stages of the oestrous cycle

Question 20

How does the cervix appear during oestrus?

Answer 20

The cervix is more relaxed and sits on the vaginal floor, with a ‘wilted rose’ appearance

Question 21

How does the cervix appear during dioestrus and anoestrus?

Answer 21

The cervis is tense and ‘pulled up’ in appearance with a visible frenulum

Question 22

What can be done to manipulate the mare’s oestrous cycle?

Answer 22

Shorten the lifespan of the corpus luteum (short-cycling)
Ovulation induction (programming)
Oestrus suppression
Oestrus synchronisation
Manipulate spring transition

Question 23

How can you shorten the lifespan of the corpus luteum?

Answer 23

Prostaglandin administration

Question 24

When is it appropriate to administer a prostaglandin injection to ‘short cycle’ a mare?

Answer 24

You can administer prostaglandin to ‘short cycle’ a mare when the corpus luteum is at least 5 days old to lyse the corpus luteum

Question 25

When will the mare go into oestrus following prostaglandin administration?

Answer 25

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

Question 26

Give an example of a prostaglandin that can be used to shorten the lifespan of the corpus luteum

Answer 26

Closprostenol

Question 27

What are the potential side effects of prostaglandin adminstration?

Answer 27

Sweating Diarrhoea Colic

Question 28

Which key factors should you be aware of when carrying out ovulation induction in mares?

Answer 28

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

Question 29

Which drugs can be used to induce ovulation in the mare?

Answer 29

Human chorionic gonadotrophin (GnRH) Deslorelin (synthetic GnRH)

Question 30

How does human chorionic gonadotrophin and deslorelin induce ovulation in mares?

Answer 30

Human chorionic gonadotrophin and deslorelin have an LH like effect on the follicle to induce ovulation

Question 31

When do mares typically ovulate following administration of human chorionic gonadotrophin?

Answer 31

36 hours post administration

Question 32

When do mares typically ovulate following administration of deslorelin?

Answer 32

40 - 42 hours post administration

Question 33

How can you synchronise oestrus in mares?

Answer 33

Progestrogen and oestrodiol injections for 10 days Prostaglandin (2 injections 14 days apart) | Synchronising oestrus in mares is very challenging

Question 34

What is the indicator for oestrus suppression in the mare?

Answer 34

Oestrus suppression is indicated to prevent unwanted oestrus behaviours

Question 35

What should you always do prior to carrying out oestrus suppression in mares?

Answer 35

Detailed history Clinical examination Reproductive examination

Question 36

Why is it so important to get a detailed history before beginning oestrus suppression in the mare?

Answer 36

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

Question 37

What can be used to suppress oestrus in the mare?

Answer 37

Altrenogest Intrauterine marble Upod Ovariectomy

Question 38

What is altrenogest?

Answer 38

Altrenogest is a synthetic progesterone agonist which suppresses oestrus in mares

Question 39

What are the benefits of oral altrenogest over injectable altrenogest?

Answer 39

Oral altrenogest is easier and cheaper to do, injectable altrenogest is more expensive, requires a veterinarian for administration and mares can get injection site reactions

Question 40

How does an intrauterine marble suppress oestrus in mares?

Answer 40

An intrauterine marble can make mares think they are pregnant and thus their body will produce natural progesterone and suppress oestrus

Question 41

What is the main disadvantage of an intrauterine marble?

Answer 41

Some mares will spontaneously expel the marble and go back into oestrus

Question 42

What is a Upod?

Answer 42

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

Question 43

What is spring transition?

Answer 43

The spring transition is a period of anovulatory receptivity where mares can exhibit 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

Question 44

How can you manipulate the spring transition?

Answer 44

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

Question 45

What are the different methods available for breeding mares?

Answer 45

Natural cover Artificial insemination *(fresh, fresh chilled, or frozen)*

Question 46

(T/F) You cannot use artificial insemination in racing thoroughbreds

Answer 46

TRUE. If you want to register the foal with Jockey club you cannot use artificial insemination, they must be produced by natural mating

Question 47

What is pasture breeding?

Answer 47

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

Question 48

What is hand mating?

Answer 48

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

Question 49

Which form of semen has the best conception rates in terms of artificial insemination?

Answer 49

Fresh semen

Question 50

When should you order fresh cooled semen?

Answer 50

You should order fresh, cooled semen when the dominant follicle has reached 30 - 35mm

Question 51

How long is fresh cooled sperm viable once it has been inseminated?

Answer 51

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

Question 52

How do you thaw frozen semen?

Answer 52

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

Question 53

How long is sperm from frozen semen viable once it has been thawed?

Answer 53

12 - 24 hours

Question 54

What is a post ovulation artificial insemination (AI) protocol in mares?

Answer 54

1. Examine and scan the mare daily until a 30-35mm dominant follicle is present 2. Administer an ovulating agent to stimulate ovulation 3. Ultrasound scan the mare to monitor for ovulation every 6-8 hours 4. 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

Question 55

What is a timed artificial insemination (AI) protocol in mares?

Answer 55

1. Examine and scan the mare daily until a 30-35mm dominant follicle is present 2. Administer an ovulating agent to stimulate ovulation 3. Inseminate with one dose at 24 hours post-ovulating agent 4. Inseminate with a second dose at 40 hours post ovulating agent

Question 56

What is a potential complication following breeding?

Answer 56

The semen can cause a reaction and infection in the mare's reproductive tract

Question 57

What should be done 24 hours post breeding?

Answer 57

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

Question 58

Why is it important to evacuate any uterine fluid or debris 24 hours post breeding?

Answer 58

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

Question 59

How can you evacuate uterine fluid?

Answer 59

Uterine lavage Oxytocin