Overview Flashcards
Role of the vet in reproductive management
Proactive
- Cycle manipulation/advancing breeding season
- Pre-breeding soundness examinations
- Use of estimated breeding values (EBVs)
Reactive
- Investigating infertility
- Abortion outbreaks
- Dystocia
Overall: to discuss targets and monitor progress
What are caruncles?
- dams placental attachment site
Shape of cow uterine horns
- curled caudally
- so that the ovary is closer to the body of uterus
- horns taper into uterine tube (oviduct) and are relatively long
The ovary: major structures
Follicle
- Contains oocyte (egg)
- Fluid filled (anechoic on ultrasound)
- Secretes oestradiol that drives oestrus
- Multiple stages of development
Corpus luteum
- Highly vascularised, transient endocrine gland
- Solid (homogenous, medium echogenicity )
- Progesterone production
Always need to visualise both ovaries when determining the stage of cycle
HPO axis
= hypothalamus-pituitary ovarian axis
melatonin works on the hypothalamus.
the hypothalamus produces GnRH, which acts on the anterior pituitary gland.
the anterior pituitary gland produces FSH which stimulates growth of the follicle and LH which triggers the release of the egg from the ovary -> ovulation.
the corpus luteum produces progesterone and oxytocin.
the astral follicle (what FSH works on) produces oestradiol
Oestrus cycle in the cow
21d oestrus cycle:
- 17 day luteal phase
- Falling progesterone = 3 days proestrus
- Standing oestrus lasts ~1 day
LH surge occurs mid-oestrus:
- Ovulation occurs 24 hours after LH surge
- Therefore, ovulation 12h after end of oestrus
Follicular phase
- large follicle(s) present with a smaller CL
Mid-luteal phase
- large mature CL present
- large follicle(s) can also be present
Oestrus in the cow (& importance for timing of insemination/mating)
Oestrous cycle length (days): 21-22d
Duration of oestrus : 5-18h
Time of ovulation: ~12h after end of oestrus
Relatively easy since oestrus is short and tightly regulated to time of ovulation
- Inseminate/mate at oestrus
- Problem: detecting oestrus
Oestrus in the ewe (& importance for timing of insemination/mating)
Oestrous cycle length (days): 17d
Duration of oestrus: 24-36h
Time of ovulation: 30-36h from beginning of oestrus (i.e. towards end of oestrus)
Not a problem since mated throughout oestrus by a ram
- AI: insemination is slightly delayed (c.f. Cow): 12h after onset of oestrus
- Key issue: correct ram:ewe ratio/identification of mated ewes
Oestrus in the sow (& importance for timing of insemination/mating)
Oestrous cycle length (days): 21d
Duration of oestrus: 48-72h
Time of ovulation: 35-45h from beginning of oestrus
Sows / boars housed separately with sow presented to the boar for mating.
- Oestrus detection is very important
- Mating and AI usually start on second day after the onset of standing oestrus. Usually, two inseminations
Return to cyclicity post-partum - mechanism of ovarian rebound
Re-initiation of HPO axis
- At parturition, pituitary isrefractory to GnRH, but
- FSH secretion initiated due to lack of negative feedback, this leads to emergence of an antral follicular wave
Resumption of full ovarian activity
- Increasing sensitivity of gonadotropes to GnRH, leading to
- Increased FSH-stimulation of oestradiol production
- Increased LH pulse frequency
- Ovulation, often accompanied by silent oestrus
- Expected time 18-25 days, but often delayed
- Short first oestrous cycle
What does anoestrus mean?
= without cyclicity
Physiological anoestrus occurs as a result of
- Gestation
- Lactation / presence of offspring (there are key species difference)
- Seasonality: Short or long-day breeders
Pathological anoestrus occurs as a result of
- Stress
– Metabolic
– Heat - Ovarian pathologies
– Cystic ovarian disorders
– Inactive ovarian activity
Ovarian rebound in the sow
Profound suckling effects:
- Early follicular activity but
- Prolactin suppresses LH secretion, thus no ovulation
- (presence of piglets suppresses final stages of follicular maturation
Return to oestrus
- Weaning ‘initiates’ oestrus and LH surge within 7 days (WOI)
- Weaning to oestrus interval (WOI) is affected by length of lactation / timing of weaning
Pharmacological control of cyclicity: key strategies
- stimulation of HPO axis
- control of oestrus/ovulation
- resolution of ovarian pathology
typically drugs are based on key endogenous hormones e.g. GnRH, PGF2a and progesterone
Gonadotrophin releasing hormone (GnRH)
- Short term action
- Hastens impending cyclicity/ return to oestrus (ie lactational anoestrus in cows, post weaning in gilts/sows)
- Hastens ovulation by inducing LH surge. It will also cause FSH release
- Part of synchronisation protocol (fixed-timed AI)
- “Force” ovulation/luteinisation of cystic structures
Gonadotrophins: FSH
Stimulates antral follicular growth
Products
- Few products are FSH specific
- Alternatively, use ECG which at low doses has mainly FSH-like activity
Clinical uses:
- Ovulation of more follicle than normal (superovulation)
- Must administer early in follicular wave for superovulation1
- Often, requires repeated doses
- Responses are varied
Gonadotrophins: LH
Stimulates final maturation of follicles, luteinisation and provides luteal support
Products
- No LH specific product
- Could use HCG which binds to LH receptor and has LH-like activity. It also can induce an immunological reaction. Thus, HCG rarely used in farm animals
Potential clinical uses: exact effect influenced by dose
- Induce ovulation when animals are in oestrus
- To force ovulation when there has been repeated failure of conception in cattle
- Treatment of cystic ovaries in cows and heifers
Exogenous progestogens:
Progesterone has a negative feedback effect upon the hypothalamus and anterior pituitary
Clinical use of exogenous progestogens (also termed ‘progestogens’)
- Will be administered for 7-14 days
- Suppress the hypothalamic-gonadal axis thus:
- Used as method of inducing/synchronising oestrus following withdrawal of the product
Vaginal
- Vaginal sponges (Flugestone [Chronogest]; ewes)
– Oestrus induction / synchronisation upon withdrawal (often in combination with eCG)
- Vaginal devices (Progesterone [PRID/CIDR]; cows)
– Oestrus induction / synchronisation (in combination with GnRH/PGF2A)
Oral
- Oral liquids (Altrenogest [Regumate]; sows)
– Oestrus suppression / induction / synchronisation in mares/sows
Prostaglandin F2ɑ
Endogenous prostaglandin F2α causes
- Lysis of the mature CL, causing progesterone to decline
- Smooth muscle contraction i.e. ecbolic effect on uterus
Thus, exogenous prostaglandin F2α causes CL regression although early CLs are usually not responsive
- Termination of luteal phase to synchronise oestrus
- Induction of abortion or parturition
- Ecbolic effect
– Treatment of chronic metritis
– Treatment of pyometra (if CL is present)
Control of oestrus and ovulation in sheep
Stimulate earlier onset of cyclicity around start of breeding season:
- Melatonin, or
- Progestogen sponges for ~14 days in combination with eCG/GnRH, or
- Ram effect
Synchronisation of breeding for management purposes
Control of oestrus and ovulation in pigs
Synchronisation of a group of sows or gilts
Enables batch of animal to farrow at similar times
- Progestogen (oral) 14-18 days with or without eCG just before P4 removal
- Limited hormonal use after weaning
- Do not use two doses of PGF as CL only responsive day 11-16
