Oestrus Manipulation Flashcards
(33 cards)
State reasons for Manipulating oestrus
- Poor oestrus detection
- Synchronisation (sheep flocks for short lambing period)
- Enable AI and ET (embryo transfer)
- Trigger post-partum resumption (pigs especially – to make sure once they have given birth they are good to go again – look at nutrition first, oestrus relies on LH which relies heavily on energy)
Recap HPO axis
Hypothalamus-pituitary ovarian axis!
1. Hypothalamus secretes GnRH which acts on Anterior lobe of pituitary, releasing FSH and LH which act on the ovary
2. FSH stimulated follicle recruitment and growth
3. LH stimulates maturation, ovulation, leutinisation of follicle, also maintains function CL once ovulation has occurred
4. The developing follicle secretes inhibin and oestrogen
5. CL secreted progesterone
6. Inhibin negative feedback to FSH,
Oestrogen adn progesterone neg feedback to LH and GnRH
List the relative concs of each hormone within the normal cycle
1. Dioestrus high progesterone as CL Oestrogen, LH and FSH low After no fertilisation, progesterone falls.... 2. Pro oestrus dec progesterone inc oestrogen Inc LH behing oestrogen inc FSH behind LH 4. Oestrus Peak Oestrogen LH surge behind peak Inc FSH OVULATION 5. metoestrus All low but progesterone rising as CL
How come FSH peak not as high as LH?
BEcuase dominant follicle secretes inhibin that negative feedbacks therefore suppresses FSH.
So FSH surge not as strong as LH
Why when cows have a few “waves” where follicles are selected before proestrus, in metestrus and diestrus, does ovulation not occur?
Because in metoestrus ad diestrus there is still a CL present which is secreting progesterone that inhibits LH and GnRH therefore FSH and LH can never get too high as are inhibited. MEaning follicles never actually reach full maturity.
Only when leutyolysis occurs and we no longer have progesterone in the system can follicles reach full mature size and ovulate.
Sometimes with cows and mares, confirm pregnancy and then owner reports oestrus signs. What does this mean?
Either:
1. lost pregnancy and back in oestrus
2. Follicles have started to grow and become large enough to just about secrete oestrogen.
May still be pregnant! so check
Oestrus detection in cows, what 2 means of measurement are there?
- Heat detection rate/ oestrus detection (HDR) = Rate means how many animals cycling can you detect in oestrus in dairy HDR = 60-80%
- Accuracy (HDA) = Rate and accuracy important. If fertility issues we asses BOTH of these
Why would you miss signs of oestrus in a cow?
- unaware of signs
- cows occupied otherwise e.g. not show sign in milking parlour
- one-third to one-half of cows start expressing oestrus after midnight
- General view has been that average duration of oestrus behaviour is 9-14 hours in cattle (with 10-14 mounts of 2 seconds each).
What are cow oestrus behavioural signs? and which is the most important?
- Stands to be mounted = only true sign
- if mounting others = approaching oestrus
- Inc activity
- chin pressing
- licking
- Sniffing
Oestrus in cows is 9-14 hr window!!
Cow physical signs of oestrus
- rising marks = usually late, may have already ovulated
2. Clean vaginal exam - clean vulva, gloved hand, insert and if thick mucus bulling string = in oestrus
Name oestrus detection aids
- Mount indicator – paint capsule will break if mounted.
- Pedometer – changes in walking activity = inc if in oestrus
- Tail paint will be rubbed off if she has been mounted
Mare - facts about oestrus
- Slightly more complicated as longer oestrus and need to predict when coming out
- Cycle on average 21 days, ranges 15 to 26 days of oestrus
- Oestrus lasts about 7 days
- Ovulate 24-48 hours before END of behavioural oestrus
- (i.e. typically 5 days after onset of oestrus)
What do we monitor when waiting fir mare oestrus?
FOLLLICLE using ultrasound:
- size
- shape
- Becomes softer
- Follicle wall thickens
- Oedema within uterus
Talk about the changes we see in mare follicle when comes into oestrus
- Size
a. Most likely to ovulate if above 35 mm diameter
b. Follicular growth about 3-5 mm / day; at ovulation; - Shape
a. change in follicular shape: teardrop shape adopted within 24 hours of ovulation in 85% of follicles - Become softer
a. within 6-12 hours of ovulation, i.e. slight indentation on manual or probe pressure - Follicle wall thickens
a. Slightly 24 hrs prior to ovulation - Oedema within uterus itself
What is the most useful mechanism to detect oestrus in the bitch?
Vaginal Cytology
• Take a smear from vaginal mucosa and look at cells present
• Di-oestrus/ anoestrys: abrupt change on Day 1 to 50% non-cornified
2. Proestrus - inc cornified cells 10% per day. The number of layers of the vaginal mucosal epithelium begins to increase in response to increased plasma oestrogen levels. These cells have a smaller and more triangular nucleus.
3. Oestrus = 100% cornified cells, no leucocytes present
4. Metoestrus =
number of vaginal mucosal epithelium layers decrease due to falling oestrogen levels and continually high progesterone levels. Cells are sloughing off and there will be an increased number of anuclear cells and presence of leucocytes is indicative of metoestrus.
Day 1 of metoestrus will de identifiable by an abrupt fall in cornified cells to only 50%
Oestrus cycle
Di oestrus/ anoestrus
Pro oestrus
Estrus
Metoestrus
What hormones shorten and lengthen cycle
- endrogenous admin progesterone lengthens cycle as it inhibits GnRH and therefore lifespan of CL - don’t come into eostrus as quickly
- Endrogenous prostaglandin F2 alpha shortens the cycle, bringing the animal into oestrus as luteolysis is driven by prostaglandin via utero-ovarian counter current
Oxytocin’s role in cycle
Secreted from posterior pituitary
binds to oestrogen receptors on endometrium
secretes prostaglandin f 2 alpha, passes v quickly to overian artery due to the utero-ovarian counter current
3. LEUTYOLYSIS
What hormone can you use to recruit follicles and make them grow?
- GnRH
- can use gonadotrophin (eCG or hCG)
GnRH would stimulate the pituitary to secrete more FSH and LH for us
Use eCG (also known as pregnant mare serum gonadotrophin PMSG) if don’t think pituitary as receptive to GnRH as we would like
What hormone can we use to make ovulate once follicles have been recruited and grown?
- GnRH
- Gonadotrophin (hCG)
NOT oestrogen as although oestrogen rises it does not cause ovulation. What causes ovulation is LH surge!
What hormone to STOP oestrus cycle
- progesterone - negative feedback on hypothalamus so nothing happens. only when remove progesterone do things start again!
What is fixed time AI used for in which cows? adn why use?
Used in beef (only if 50 days after pp as not cycling yet due to sucklers. AND dairy
Going in BLIND. Much quicker to inject than exmin
Describe Fixed time AI in DC and BC less than 50 days pp
BLIND - don’t knwo what part of cycle each is at
• Day 0 GnRH to synchronise new follicular wave:
o If already follicle, it will be triggered to ovulate and new follicular wave starts
o If no follicle it won’t do anything
• Day 7 – prostaglandin f 2 alpha to cause luteolysis
• Day 9 – GnRH as got rid of CL, triggered new wave of follicles, triggers new wave of follicles which should be ready to ovulate day 9
• Day 10 AI
Why is fixed (blind) AI different in heifers?
under less metabolic stress and demand so simpler system:
• 2X doses PGF2 alpha, 11 days apart
• Inseminate at 72 and 96 hrs after second dose
• Or inseminate after 84 hrs
—————————–
1st PGF2
• Heifer with CL: luteolysis new follicle ovulation & 11 days time, new CL
• Heifer with follicle: prostaglandin won’t do anything. Follicle continue growing. Ovulation & CL forms. But quicker to inject than examin
• 11 days time both groups will have CL
2nd PGF2
1) All have CL luteolysis new follicle ovulation, inseminate 3/4days later
