Oestrus cycle Flashcards
where is GnRH produced?
hypothalamus
where is FSH and LH produced?
pituitary gland
what triggers FSH and LH release?
GnRH
what does GnRH trigger to be released?
FSH and LH
what does FSH do?
stimulates the development of follicles in thew ovary (follicle stimulating hormone)
what does LH do?
causes the dominant follicle each cycle to ovulate and then has an effect on the follicle after ovulation to cause it to luteinize and create a corpus luteum
what is contained with a follicle?
fluid and an oocyte
what hormone does the follicle produce?
oestrogen
what effect does oestrogen have?
prevents further follicle stimulation (only get one primary follicle)
makes animal show signs of heat
what does the corpus luteum develop from?
the follicle
what hormone is produced by the corpus luteum?
progesterone
what is the function of progesterone?
prepares uterus for pregnancy and maintains the pregnancy
what are the stages of a follicle developing into a corpus luteum?
follicle
corpus haemorrhagicum
corpus luteum
how long before ovulation do the primordial follicles become responsive to FSH and LH?
3 months before ovulation
why is it important to know that primordial follicles become responsive to FSH and LH 3 months before ovulation?
health of cow three months prior to that ovulation can effect quality of oocyte/ovulation
how long is an ovulatory follicle present for?
around 24 hours
how does stress/poor nutrition effect LH release?
reduce the pulse quality/frequency meaning an animal won’t ovulate
what effect does oestradiol have on GnRH, FSH and LH?
negative feedback (prevents another follicle developing)
how soon after calving do dairy cows return to cycling?
within a couple of weeks
how long is the normal oestrus cycle of a cow?
21 days (+/- 2)
what effect does progesterone have on a follicle?
makes them bigger and produce more oestradiol
why is the first oestrus cycle after calving often silent?
the follicle hasn’t been exposed to progesterone as there hasn’t been a cycle before is, hence it will be smaller and not produce as much oestrodial meaning she may not show oestrus behaviour
what are the stages of a follicular cycle?
emergence
selection
dominance
atresia
what stage of the oestrus cycle follows oestrus?
metoestrus
how is metoestrus detectable?
blood in vaginal discharge
ovaries very small on rectal examination
what stage follows metoestrus?
dioestrus
what happens during dioestrus?
CL is the dominant structure on one of the ovaries and producing progesterone
what event causes dioestrus to turn into proestrus?
loss of CL
how often is a pulse of LH released during the normal cycle (baseline LH)?
low levels every 3 or 4 hours
how often is a pulse of LH released in the lead up to ovulation?
every hour
what allows the LH to surge?
drop in progesterone due to luteolysis allowing the LH to pulse more frequently
how do the number of waves per oestrus cycle in dairy heifers compare to that of high yielding cows?
dairy heifers have more (3) as they have more energy available
what does the success of AI depend on?
oestrus detection
operator and semen
what is the most reliable sign of oestrus?
standing to be mounted
what is the average length of oestrus?
18 hours
if a cow is sniffing another vulva, which one is in heat?
the cow sniffing
if a cow is chin resting, bunting or licking another, which one is in heat?
both of them or either of them
if a cow mounts another cow but at its head end, which one is in heat?
the cow mounting
if a cow mounts another cow, which is in heat?
the one standing to be mounted
when should AI be timed in relation to standing heat?
if she is seen standing in the morning serve her in the evening (AM/PM rule)
when should sperm be inseminated in relation to ovulation?
a few hours before ovulation
what can be done to improve heat detection?
mount detectors
record keeping (check cows 18-24 days after last heat)
teaser animals
milk progesterone
activity monitors
how can milk progesterone be used to aid heat detection?
check progesterone in milk everyday, when they come into oestrus the progesterone drops
how much does the activity have to change for it to be considered in heat by an activity monitor?
increased by 5 standard deviations from the mean activity level
how does rumen activity change when an animal is in heat?
decreases
how many sperm are in an AI straw compared to an ejaculation?
billions in an ejaculation
millions in a normal straw
million in a sexed straw
what should be considered if you are getting reduced pregnancy from AI?
has the flask thawed
thawed at right temperature and rate
dry thoroughly
staff training
test straws
