Oestrus cycle

Question 1

where is GnRH produced?

Answer 1

hypothalamus

Question 2

where is FSH and LH produced?

Answer 2

pituitary gland

Question 3

what triggers FSH and LH release?

Answer 3

GnRH

Question 4

what does GnRH trigger to be released?

Answer 4

FSH and LH

Question 5

what does FSH do?

Answer 5

stimulates the development of follicles in thew ovary (follicle stimulating hormone)

Question 6

what does LH do?

Answer 6

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

Question 7

what is contained with a follicle?

Answer 7

fluid and an oocyte

Question 8

what hormone does the follicle produce?

Answer 8

oestrogen

Question 9

what effect does oestrogen have?

Answer 9

prevents further follicle stimulation (only get one primary follicle)
makes animal show signs of heat

Question 10

what does the corpus luteum develop from?

Answer 10

the follicle

Question 11

what hormone is produced by the corpus luteum?

Answer 11

progesterone

Question 12

what is the function of progesterone?

Answer 12

prepares uterus for pregnancy and maintains the pregnancy

Question 13

what are the stages of a follicle developing into a corpus luteum?

Answer 13

follicle
corpus haemorrhagicum
corpus luteum

Question 14

how long before ovulation do the primordial follicles become responsive to FSH and LH?

Answer 14

3 months before ovulation

Question 15

why is it important to know that primordial follicles become responsive to FSH and LH 3 months before ovulation?

Answer 15

health of cow three months prior to that ovulation can effect quality of oocyte/ovulation

Question 16

how long is an ovulatory follicle present for?

Answer 16

around 24 hours

Question 17

how does stress/poor nutrition effect LH release?

Answer 17

reduce the pulse quality/frequency meaning an animal won’t ovulate

Question 18

what effect does oestradiol have on GnRH, FSH and LH?

Answer 18

negative feedback (prevents another follicle developing)

Question 19

how soon after calving do dairy cows return to cycling?

Answer 19

within a couple of weeks

Question 20

how long is the normal oestrus cycle of a cow?

Answer 20

21 days (+/- 2)

Question 21

what effect does progesterone have on a follicle?

Answer 21

makes them bigger and produce more oestradiol

Question 22

why is the first oestrus cycle after calving often silent?

Answer 22

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

Question 23

what are the stages of a follicular cycle?

Answer 23

emergence
selection
dominance
atresia

Question 24

what stage of the oestrus cycle follows oestrus?

Answer 24

metoestrus

Question 25

how is metoestrus detectable?

Answer 25

blood in vaginal discharge
ovaries very small on rectal examination

Question 26

what stage follows metoestrus?

Answer 26

dioestrus

Question 27

what happens during dioestrus?

Answer 27

CL is the dominant structure on one of the ovaries and producing progesterone

Question 28

what event causes dioestrus to turn into proestrus?

Answer 28

loss of CL

Question 29

how often is a pulse of LH released during the normal cycle (baseline LH)?

Answer 29

low levels every 3 or 4 hours

Question 30

how often is a pulse of LH released in the lead up to ovulation?

Answer 30

every hour

Question 31

what allows the LH to surge?

Answer 31

drop in progesterone due to luteolysis allowing the LH to pulse more frequently

Question 32

how do the number of waves per oestrus cycle in dairy heifers compare to that of high yielding cows?

Answer 32

dairy heifers have more (3) as they have more energy available

Question 33

what does the success of AI depend on?

Answer 33

oestrus detection
operator and semen

Question 34

what is the most reliable sign of oestrus?

Answer 34

standing to be mounted

Question 35

what is the average length of oestrus?

Answer 35

18 hours

Question 36

if a cow is sniffing another vulva, which one is in heat?

Answer 36

the cow sniffing

Question 37

if a cow is chin resting, bunting or licking another, which one is in heat?

Answer 37

both of them or either of them

Question 38

if a cow mounts another cow but at its head end, which one is in heat?

Answer 38

the cow mounting

Question 39

if a cow mounts another cow, which is in heat?

Answer 39

the one standing to be mounted

Question 40

when should AI be timed in relation to standing heat?

Answer 40

if she is seen standing in the morning serve her in the evening (AM/PM rule)

Question 41

when should sperm be inseminated in relation to ovulation?

Answer 41

a few hours before ovulation

Question 42

what can be done to improve heat detection?

Answer 42

mount detectors
record keeping (check cows 18-24 days after last heat)
teaser animals
milk progesterone
activity monitors

Question 43

how can milk progesterone be used to aid heat detection?

Answer 43

check progesterone in milk everyday, when they come into oestrus the progesterone drops

Question 44

how much does the activity have to change for it to be considered in heat by an activity monitor?

Answer 44

increased by 5 standard deviations from the mean activity level

Question 45

how does rumen activity change when an animal is in heat?

Answer 45

decreases

Question 46

how many sperm are in an AI straw compared to an ejaculation?

Answer 46

billions in an ejaculation
millions in a normal straw
million in a sexed straw

Question 47

what should be considered if you are getting reduced pregnancy from AI?

Answer 47

has the flask thawed
thawed at right temperature and rate
dry thoroughly
staff training
test straws