Equine Flashcards
(168 cards)
What type of breeder is the mare?
Seasonally poyoestrus
Long-day breeders
When is the thoroughbred breeding season?
March through to July
When is a mare in cyclic oestrus in the northern hemisphere?
April to mid-August
What is the main thing that causes the change in seasonal cyclic activity?
Increasing daylight length
What are the three main things that control seasonal cyclic activity?
Reduced melatonin secretion by pineal gland
Reduced GnRH inhibition from hypothalamus
FSH and LH secreted by anterior pituitary gland
Describe how the pineal gland can affect seasonal cyclic activity in the mare
Gland interprets daylight length and regulates melatonin secretion
Melatonin nocturnally produced by pituitary gland
Inhibits Hypothalamic-Pituitary-Ovarian axis
Daylight increases then melatonin level decreases and inhibition of HPO axis downregulated
Leads to GnRH production by hypothalamus
What are some other factors in the mare that can play a role in the transition from anoestrus to normal cycling?
Nutrition
Age
Breed
What is needed for a mare to be able to return to cyclicity?
Large enough quantities of GnRH
Stimulate FSH and LH production by pituitary
What are the three functional seals between the uterus and exterior?
Vulva, cervix and vestibule
What happens to the perineal conformation with age and multiparity?
Abdomen sinks
Anus displaces cranially
Upper commissure of vulva dragged cranially - sloping vulva
What are older, multiparous mares more predisposed to due to their altered perineal conformation?
Pneumovagina
Cervicitis
Endometritis
Describe control of cyclic activity from FSH stimulation to luteinisation
FSH stimulates ovarian follicles
Follicles secrete oestrogen - behaviour change, tract changes, LH stimulation
Follicles secrete inhibin - inhibit FSH secretion
LH stimulates ovulation and luteinisation
Follicle collapses and luteinises - oestrogens and inhibin cease
Describe control of cyclic activity from corpus luteum formation to PGF2alpha secretion
Corpus luteum secretes progesterone - tract changes, behaviour changes
If conception maternal recognition occurs at 14 days post ovulation
Recognition causes blastocyst capsule oestrogens to be produced - prevent endometrial gland secretion of PGF2alpha
No recognition causes endometrial gland secretion of PGF2alpha
Describe control of cyclic activity from PGF2alpha secretion to FSH stimulation
PGF2alpha causes luteolysis of CL
CL stops progesterone secretion
Inhibition of: sexual behaviour, tract changes, LH secretion
Cervix opens
FSH secretion stimulates ovarian follicles
Describe a mares behaviour in oestrus
Submissive Ears forward Legs straddled Tail held high Urinating Everting clitoris
Describe a mare in dioestrus
Violent
Ears back
Screaming
Tail clamped down
Describe the change in each of the 5 hormone levels over one cycle in a mare
Oestrogen - starts to increase day 17, peaks day 3-5, decreases from day 5 until day 10
Progesterone - Increases rapidly from day 5, peaks at day 8 until day 14, drops until day 20
LH - maintains a low base level, increases from day 1, peaks at day 7, rapidly decreases from day 7 until day 12
FSH - maintains low base level, increases from day 3, peak at day 6, drop between days 6 and 8, increases to a higher peak on day 10, decreases on day 10 back to base level on day 14
PGF - maintains a low base level, increases from day 13, peaks at day 15, decreases from day 15 back to base level on day 17
What day of the cycle does ovulation occur?
Day 5
How long is oestrus in the mare?
5 days
Describe hormonal changes during equine pregnancy
Blastocyst capsule secretes oestrogens from day 14
2nd wave of ovarian follicles ovulate and produce progesterone
Chorionic girdle forms endometrial cups which secrete eCG from day 35-100
Foetal gonads secrete oestrone sulphate from day 100-term
What are the four layers of the scrotum?
Skin - sweat glands
Tunica dartos - smooth muscle raises and lowers the testes
Fascia - allows mobility for vertical and lateral movement
Vaginal tunic - abdominal cavity through inguinal canal to bottom of scrotum, watery fluid facilitating movement
What varies in the male horse from month to month?
Testicular function
Semen constituents
Hormone levels
What is the size of mature horse testicles?
80-100mm long
50-80mm wide
225gm weight
When does the pre-pubertal stage in the male horse begin?
Around 6 months of age