Repro Endocrinology LA Flashcards
How may oestrus/ovulation be induced in the anovulatory post-partum cow or seasonally anoestrus ewe biologically?
Sustained increase in LH pulse frequency
How may LH pulse frequency be affected?
- environmental factors eg. seasonal, day length, pheremones
- physiological factors eg. post partum, lactation, pre-pubertal
- pathological factors eg. uterine disease/endotoxins
What hormones has a negative feedback effect on pulsatile LH?
Oestradiol E2
What may be given artificially to impact LH pulse frequency?
GnRH in a pulsatile manner (2 hourly)
What should first be checked in an anovulatroy anoestrus/acyclical cow? What are the first steps in Tx?
- true anoestrus not just a case of inefficient oestrus detection
- correct underlying factors fisrt eg. negative energy balance, suckling/maternal bond, diseases eg. lameness, uterine infection
What hormonal based treatment of anovulatory anoestrus/acyclycity in cows can be implemented once underlying factors have been corrected?
- PRID or CIDR for 12d
+- 500 iu eCG on day of removal
What repro hormone based Tx can be used to induce oestrus/ovulation in seasonally anoestrus ewes?
- P4 sponge on day 0
- Remove P4 sponge on day 12
- PMSG/eCG injection 500 iu at
- > freq LH pulses ^
- add rams 24 hours later
What alternative Tx may be used to treat anoestrus ewes? Why is this not common? How else can this system be manipulated?
- manipulation of photoperiod [difficult practically] 16h dark: 8h light
- melatonin implants -> ear can also be used
Give egs of melatonin implants
Regulin
Melovine
What is the ram effect?
- sound, sight and smell, perception of male by females
(may be visual/physical contact, may be pheromones) - potential endocrine mechanism
-> ewes ovulating 3-4d later
What is important to do before addition of any hormonal treatment in sheep?
P4 priming with sponge for 12d
- otherwise CL likely to be defective
How is puberty induced in gilts? What else is this indicated for?
> PG600 IM - combination of PMSG+hCG
- to induce puberty given at 100kg BW or 6-7months
- prevention of delayed puberty given at 8mo
- prevention of anoestrus if given on day of weaning
- Tx of anoestrus at d8-10 post weaning
- prevention of anoestrus due to seasonal influence on day of weaning
How does Tx with PMSG/eCG differ in mechanism of action to giving GnRH?
- no increase in endogenous FSH/LH as PMSG/eCG/hCG mimic the action of LH/FSH themselves
What are the advantages of synchronising oestrus in dairy cows?
- avoid oestrus detection
- fixed time AI
- ^ preg rates
How is synchronisation of oestrus achieved in dairy cattle?
> control of luteal phase and/follicular growth
- PGF2a -> CL lysis and shortening of luteal phase
- Ovsynch - follicular wave synchrony (using GnRH) + PGF2a
- Follicular wave synchrony with exogenous P4 (PRID/CIDR) + PGF2a to extend luteal phase??!! LOOKO UP
What causes luteolysis in the cow?
- PGF2a synthesis by uterine endometrium released into uterine vein
- diffuses into uterine artery (counter-current exchange)
Which hormone is high in the luteal phase?
Progesterone
How does PGF2a function? What is its ultimate effect? Is it reliable?
- rapid decline of P4 due to CL lysis
- oestrus 3-5 (range 2-7) days later
- single injection not sufficient to synchronise whole herd as dependant on responsive CL presence.
- heat detection still necessary if single injection given
- pregnancy rates acceptable
How long is the cows oestrus cycle?
18-24 (21) d
What are potential reasons for poor synchrony when using PGF2a?
> failure of luteolysis
- non-responsive CL, luteolytic from d6 of oestrus cycle (Tx too early in luteal phase)
- incorrect injection technique
timing dependent on follicular wave stage
- late wave takes v time -> ovulation from time of injection cf. early follicular phase
How may injection of PGF2a techniques be improved to overcome synchrony problems?
- Dx CL, inject and observe
- 2 doses, 11 days apart to ensure responsive CL presence
+ fixed time AI [2+2 or 2+1 method]
What are the 2+2 and 2+1 methods?
> 2+1: 2 doses of PGF2a + fixed time AI @ 72 and 96hrs
> 2+2: 2 doses of PGF2a + fixed time AI @ 84hrs
What is ovsynch?
> follicle wave synchrony with GnRH + PGF2a
- GnRH on d0 [if dom follicle present -> ovulation, if immature -> attrition], PGF2a on d7 [-> luteolysis]
- GnRH again on d9 [induce LH surge and ovulation]
- AI on d10
What else may be used in lieu of GnRH for ovsynch?
P4 (PRID/CIDR) fro 8d pre PHF administration
How may establishment of pregnancy be affected?
- controlled by P4 (uterine secretions and endometrial structures)
- compromised by insufficient rise post-ovulation (result of a defective CL)
- ruminants: IFNt
- pigs: oestrogens
How may pregnancy be detected in the dairy cow? Problems with this?
P4 in the milk
- cannot differentiate between cyclic rise and pregnancy rise in the first 2 weeks after insemination
Is P4 supplementation effective to improve pregnancy rates?
- usually is effective
- variable effectiveness depending on when P4 started
- best when started <6d after AI (?)
When is P4 supplementation most effective?
- herds with low pregnancy rates
What can be given as an alternative to P4 supplementation?
- GnRH day 11 after AI (cows)
- GnRH day 9 after mating (sheep)
What is COD and why does it occour?
> cystic ovarian disease
- result of defect in ovulatory mechanism due to failure of pre-ovulatory LH surge
- contributing factors = stress, v oestradiol, v hypothalamic sensitivity to oestradiol, uterine infection, NEB
What is NEB?
Negatvie energy balance
What is the Tx of LUTEAL cysts?
PG
- in heat after 3-4d
What is the Tx of FOLLICULAR cysts?
NOT manual rupture!
- GnRH or hCG
- luteinises cyst or other follicles
[may secrete E2]
What is the Tx of pyometra?
PGF2a (pyometra due to persistent CL)
What is the Tx of pseudopregnancy in goats?
PGF2a (pseudopregnancy due to persisnt CL)
What are the objectives of induced parturition?
- synchronise calving with seasonal grazing
- ensure calving coincides with availability of labour
- therapeutic termination of pregnancies for various clinical reasons
How is parturition initiated in the cow, sheep, goat and sow?
- foetus initiates by stopping P4 production by CL or placenta
- foetal PA axis determines timing of onset of parturition - cortisol production in foetal adrenal
- > ^ oestrogen:progesterone ratio
how does cortisol affect onset of parturition differently in goat, cow and sow cf. sheep
> goat, cow and sow
- cortisol -> aromatising enzymes (placenta)
- DHA (from foetal adrenal) converted to oestrogens in placenta
-> ^PGF2a
- CL regression, v P4 and ^ E2
Sheep
- cortisol affects multiple enzymes in Progesterone -> oestrogen pathway itself
-> Prostaglandins -> cervical softening, ^ myometrial contractions
What 2 general ways may ovulation rate increase s be achieved?
- ^ follicular recruitment
- v atresia
What does ^ FSH case?
^ follicle recruitment
How may superovulation be achieved?
> Giving FSH analiogues
- recombinant FSH
- pFSH
- oFSH
- eCG (PMSG)
- purified porcine pituitary extract (PPPE)
What is flushing and what does it cause?
- ^ plane of nutiriton before mating
- ^ energy intake LOWERS oestradiol concentration and promotion of FSH
- > recruitment of follicles
Which 2 hormones may be controlled immunologically?
- Androstendione
- GnRH
How is immunisation against androstenedione effective? Give examples of these products.
- removed neg feedback on hypothalamus and pituitary -> ^FSH -> ^ follicles -> ^ ovulation rate in sheep
- commercial product (Fecundin) single injection
- androvax plus
- ovastim
How is immunisation against GnRH effective? Give examples of these products.
- inhibits production of gonadotrophins and gonadal steroids
- v testicular size and function
- controls aggression and v male-associated odours
- eg. vaxstrate (cattle)
- equity (horses)
- gonacon (white-tailed deer)
- IMPROVAC (control of boar taint)
- spayvac (multiple spp. including wild animals)
