Bovine Oestrus Cycle Flashcards
Which oestrus related hormones are produced in the pituitary gland?
FSH
LH
What are the roles of FSH and LH?
FSH – stimulates follicle development in the ovary
LH – causes the dominant follicle to ovulate
Where is oestrogen produced?
From the follicle
What are the functions of oestrogen?
Stops further FSH production
Dictates signs of heat being shown
Describe once happens once a follicle ovulates?
Follicle bursts and the egg is released
Corpus luteum grows
Corpus luteum produces progesterone which prepares the uterus for pregnancy
Which hormone causes the pituitary gland to produce LH and FSH?
GnRH
Describe the ovaries post-ovulation
Large follicle has gone
Left with small residual follicles
Ovaries are small
Name the gland used in some species to influence reproduction that is involved in seasonality
Pineal gland
Where is GnRH released from?
The hypothalamus
Which hormones produced in the ovaries have +ve and -ve feedback on the brain?
Oestradiol
Inhibin
Describe the stages follicles go through before ovulation
- Primordial follicular pool
- Primary follicles initiated for growth
- Antrum formation
- Recruitment: some atresia of follicles occurring
- Selection and dominance of follicles: more atresia
- Single dominant follicle that ovulates
Name the 4 stages of a cows cycle
Oestrus
Metoestrus
Dioestrus
Proestrus
The levels of progesterone are high during which phase of the cycle?
Dioestrus
From ovulation, how many days does it take for the CL to reach maturity?
6 days - get a gradual increase in progesterone following ovulation
From day 6, for how many days is progesterone secreted at maximal levels?
Until around day 16 - then luteolysis occurs and the CL is destroyed
Describe the cycle following luteolysis
Sudden progesterone drop ready for the next ovulation
Describe follicular waves throughout the cycle
During the period of dioestrus (high progesterone levels) follicles do continue to develop in waves; however, hormone interactions prevent ovulation.
How does a high yield influence a cows cycle?
They are likely to have less follicular waves per cycle
Compare the return to cyclicity in dairy vs beef cows
Dairy cows will return to cyclicity very soon post calving but beef cows can be up to 3 months before cyclicity returns
How does the emergency of the 1st follicular wave (days post partum) differ in dairy vs beef cattle?
It doesn’t, tends to be between 5-10d post calving
How does the % of cows that ovulate the first dominant follicle differ in dairy vs beef cattle?
Dairy = 50-80%
Beef = 20-35%
How does the days to 1st oestrus differ in dairy vs beef cattle?
Dairy = 25-45
Beef = 30-130
- Nature of the first ovulation is silent in both
Success of AI depends on which two factors?
Use of proven/fertile sires
Reliable oestrus detection
List the signs of oestrus detection - describe which cow is in oestrus when these signs take place
- Sniffing of the vulva: cow sniffing the vulva is in oestrus
- Chin resting: both cows involved are in oestrus
- Licking: both cows
- Bunting: both cows
- Mounting head to head: cow mounting is in oestrus
Which sign has the shorting duration during heat?
Standing to the mounted
Which oestrus behaviours have the highest occurance?
Sniffing
Chin resting
Mounting
How can steps be used to monitor oestrus
Usually an increase in steps/hr when in oestrus
How long is the duration of standing heat?
Between 3-15hrs
High % only for 3 hours so easy to miss
What is the am/pm rule?
If you see a how standing to be mounted in the am, then serve in the pm. And vice versa
If more cows are in heat, what does this influence?
How obvious the signs are
Describe the use of mount detectors
- Paint / chalk or Kamar/Ambic
- A cow is detected only when stands to be mounted - not all animals show standing heat
- Threshold is important
- Easy to use, but maintancence can be time consuming
Describe some other possible aids for oestrus detection/monitoring
- Record keeping
- Teaser animals
- Chinballs
- Monitors milk progesterone - everyday for every cow
- Activity monitors
Describe ‘heattime’ as a method of oestrus monitoring
- Basal activity of each cow is calculated
- If her activity increases beyond the mean +5 S.D then it is noted that she is showing oestrus behaviour
- Same efficiency of farm staff (but still around 40% of heats not detected)
- Ideally used in combination
How many sperm are in the following:
1. ejaculate
2. in a normal straw of conventional semen
3. in a straw of sex sorted semen
- Billions
- 15-20 million
- 1 million
Where are sperm deposited?
in the body of the uterus or into one horn
Describe the AI routine
- Thaw @ 37 deg. for 40 seconds
- Dry thoroughly
- Load gun, snip off end of straw
- Disposable sheath
- Keep warm
- Chilling once thawed bad!
- Thaw one at a time!
- Get AI company to test some straws or do yourself
Things to consider if reduced pregnancy rates following AI =?
- Has flask become empty, and sperm thawed then refrozen?
- Have they used fingers rather than tweezers
Name the stages of initial oocyte and embryonic development
- First cleavage
- Embryonic genome activation
- Morula compaction
- Blastocyst formation
Which hormone is crucial for embryo growth?
Progesterone
Describe how luteolysis or maternal recognition of pregnancy occur
OT-R = oxytocin receptors – in the endometrium
- Prostaglandins destroy the CL if there is no embryo implantation
- If there is maternal recognition of pregnancy progesterone production continues and OT-Rs don’t develop. There is minimal PGF2a and there is no lysis of the CL
In a bovine pregnancy when is it visible on a scan/palpation
About day 27-28
The level of which hormone build up towards the end of the pregnancy?
Oestrogen
Calving is controlled by?
The calf
Which hormone produced by the calf triggers parturition
Cortisol
