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oestrus cycle and preparing mares for breeding season

Terms in this set (23)

What kind of oestrous cycle do mares have and how long?
Seasonally polyoestrus (cycles from april to october naturally)
Oestrous cycle is 21 days- 2-4 days in oestrus (follicular phase) and 15-17 days in dioestrus (luteal phase)
What hormones control when a mare cycles and how?
Increased melatonin production by pineal gland in winter months (darker) which inhibits production of GnRH by hypothalamus. In spring/summer, with increased light, there is reduced melatonin thus reduce negative feedback on hypothalamus GnRH production
What are the 5 main environmental factors that influence cycling?
Describe the cycle of the mare- particularly what hormones are important and when?
To get a mare cycling in February when should you start implementing artificial controls including light, warmth, nutrition, GnRH implant and dopamine antagonists?
Mid-December- it takes about 6 weeks for these to take effect
What are the natural and official breeding seasons?
Natural- april- october
Official- 15th February-15th July (to aim for birth as close to 15th Jan as possible)
After foaling how long before the mare can be ready to cycle again?
7-9 days (quick recovery)
What is transitional oestrus? What is it characterised by? What drugs are given to shut the repro cycle down?
Coming out of anoestrus the mare is showing interest but not ovulating. She develops spring ovaries- looks like a bunch of grapes- no follicles become dominant.
IM progestagen and oestradiol is given followed by PGF2a
Behavioural oestrus can be induced in anoestrus mares by a single IM injection of what?
Oestradiol benzoate
What two drugs can be used to induce ovulation within 48 hours?
Human Chorionic gonadotrophin (hCG) as a single IV injection- LH-like in action
or
Desorelin (Ovuplant)- a GnRH analogue in implant form- causes LH release

Both can only be used when a follicle >3cm in size is present
When the mare is in dioestrus, luteolysis can be induced with a single injection of what?
PGF2a or one of its analogues (estrumate or prosolvin)
As part of a routine gynaecological examination, the mare needs to be screened for venereal disease. What 3 organisms must we make sure she is free of?
Where is the swab taken from and what media must be used for transport?
Taylorella equigentalis (CEM)
Psedomonas aeruginosa
Klebsiella pneumonia (1,2, and 5)

Take clitoral swab and use charcoal agar (sensitive to light)
What 3 seals of the mares reproductive system must be assessed?
1- vulval lips
2- vestibular seal (where vagina collapses on itself)
3- cervical seal
What is the perineal conformation and what is the ideal?

Sinking in of the anus is normal with age. What procedure is done to correct this?
The angle between the anus and the vulva. Ideally it should be a straight vertical line between the two so that the vulva doesnt get contaminated with faeces.
Caslicks operation
What will the entrance to the cervix look like in oestrus and dioestrus?
Oestrus- open/relaxed, red, wet

Dioestrus- pale pink, puckered, tacky
The following photos show cytology of endometrial lining of the cervix. Which is normal and abnormal and what indicates this?
Left photo is normal
- endometrial epithelial cells with whispy cytoplasm and large oval nuclei

Right photo shows some endometrial cells with neutrophils- infection present?
The following photo is a ultrasound cross section of two uterine horns. Which is in oestrus?
The left is in oestrus- can see orange segment pattern
Mares should be scanned 2 days after covering/mating. What might the presence of fluid in the uterus indicate?
Fluid is normal after mating- inflammatory reaction to presence of foreign ejaculate. But this should clear after 2 days
What are the signs of oestrus?
Ears forward
leaning towards the stallion
straddle stance
urinating
clitoral winking
How common are twin ovulations?
15-43%
An endometrial biopsy can be taken to diagnose CDE (chronic degenerative endometrial disease)/Endometrosis- collective term to describe the wide range of degenerative changes (gland nests, fibrosis, excessive lymphatic lacunae) of the endometrium of the uterus seen with age. How is endometrosis expected to vary with age?
- mare up to 9 yrs old should have no endometrosis
- 9-13 yrs- mild CDE- 90% foaling rate
- 13-17 yrs- moderate CDE- 70% foaling rate
- 17+ yrs- severe CDE- <10% foaling rate
Why is being able to predict ovulation crucial to breeding?
The ovum has the best chance of being fertilised between 12-24 hours after release. Mare needs to be covered as close to ovulation as possible and the mare should be covered only once to reduce inflammatory response
Where is the site of fertilisation? When does the embryo move to the uterine horns then the uterus and how?
Egg is fertilised in the oviducts/ fallopian tubes. An unfertilised egg remains locked in the oviducts. On day 4-6 the embryo is transported to the uterine horns by the oviduct, and around day 5 embryo releases PGE to stimulate movement into the uterus
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