Endocrinology Flashcards
What are the two objectives in reproductive endocrinology in farm animals?
Optimize fertility or reinstate normal reproductive activity by - overcoming natural limitations, overcoming disease limitations
Increase reproductive efficiency to improve overall production performance
What are the eight ways endocrinology is applied to farm animals?
Reinstating reproductive activity in healthy animals Induction of puberty in gilts Synchronization of oestrus/ovulation Enhancement of embryo survival Treatment of reproductive diseases Control of parturition Increasing the number of gametes Immunological control of reproduction
What two things could intervention for artificial reproductive control in large animals be?
Stimulatory
Inhibitory
What do the problems and methods with manipulation of reproduction in large animals need to be?
Problem clearly defined - e.g. true anoestrus vs insufficient oestrus detection
Methods specific and ideally reversible - e.g. castration vs immunisation against GnRH
What are the two times we want to reinstate reproductive activity in farm animals?
Induce oestrus/ovulation in anovulatory post-partum cow
Induce oestrus/ovulation in seasonally anoestrus ewe
What is the main way of reinstating reproductive activity in adult healthy animals?
Have a sustained increase in LH pulse frequency
What does an increase in estradiol cause in farm animals?
Negative feedback effect on pulsatile LH
How do you treat anovulatory anoestrus/acyclicity in the cow?
Ensure true anoestrus not inefficient oestrus detection
Correct underlying factors first
PRID or CIDR for 12 days
PRID or CIDR for 12 days with 500 iu eCG on day of removal
How is oestrus/ovulation induced in seasonally anoestrous ewes?
Pulsatile GnRH
Manipulation of photoperiod
What are some examples of melatonin implants for farm animals?
Regulin
Melovine
What would an injection of PMSG/eCG at P4 sponge removal cause in ewes?
Increase in LH pulse frequency
Induction of ovulation
What is the ram effect?
Introducing a ram to induce ovulation
What is the indication for PG600 (PMSG and hCG) in prepubertal gilts? When is it administered?
Puberty induction - at 6-7 months of age, 100 kg bodyweight
Prevention of delayed puberty - 8 months or over
What is the indication for PG600 (PMSG and hCG) in first litter sows? When is it administered?
Prevention of anoestrus - on day of weaning
What is the indication for PG600 (PMSG and hCG) in multiparous and first litter sows? When is it administered?
Treatment of anoestrus - at day 8-10 after weaning
What is the indication for PG600 (PMSG and hCG) in multiparous and first litter sows (seasonal anoestrus)? When is it administered?
Prevention of anoestrus due to seasonal influences - on day of weaning
How can oestrus synchronisation be achieved in farm animals?
Control of luteal phase
Control of follicular growth
What three things does synchronisation of oestrus allow in farm animals?
Avoidance of oestrus detection
Fixed time AI
High pregnancy rates
What are the three ways to synchronise oestrus in farm animals?
Prostaglandin F2alpha - shortening of luteal phase
Ovsynch (follicle wave synchorny with PGF2alpha - follicular wave synchrony with GnRH and shortening of luteal phase
Exogenous progesterone with PGF2alpha - follicle wave synchrony with P4 and extension of luteal phase
What is seen with application of PGF2alpha in farm animals?
Rapid decline of progesterone with oestrus 3 to 5 days later
What are the possible reasons for poor synchrony using PGF2alpha to synchronise oestrus in farm animals?
Luteolysis fails - non-responsive corpus luteum, treated too early in luteal phase, incorrect injection technique
Timing dependent on follicular wave stage
What methods can be used to overcome problems using PGF2alpha for oestrus synchronisation in farm animals?
Diagnose corpus luteum, inject and observe
Two doses 11 days apart - ensure responsive corpus luteum presence
How does “Ovsynch” work in farm animals?
Use GnRH to synchronise new wave emergence
Apply PGF2alpha to cause luteolysis
GnRH used again to control ovulation time
AI
What four things does establishment of pregnancy affected by?
Depends on communication between mother and embryo
Controlled by progesterone
Compromised by insufficient rise in post-ovulatory progesterone - defective corpus luteum
Ruminants (interferon tau) and pigs (oestrogens)
What can be provided to farm animals with luteal deficiency or poor maternal recognition of pregnancy?
Progesterone supplementation
GnRH - day 11 in cows, day 9 in ewes
What does cystic ovarian disease occur as a result of in farm animals?
Defect in the ovulatory mechanism due to failure of the pre-ovulatory LH surge
What factors contribute to COD in farm animals?
Stress Lower oestradiol concentrations Lower hypothalamic sensitivity to oestradiol Uterine infection Negative energy balance
What is the treatment for luteal cysts in farm animals?
Prostaglandin
What is the treatment for follicular cysts in farm animals?
NOT manual rupture
GnRH or hCG - luteinises cyst or other follices
What is the treatment for pyometra in farm animals and psuedopregnancy in goats?
PGF2alpha
What are the objectives of induced parturition in farm animals?
Synchronize calving with seasonal grazing
Ensure calving coincides with availability of labour
Therapeutic termination of pregnancies for clinical reasons
What intiates parturition in the cow, sheep, goat and sow?
Foetus
How is parturition started in the cow, sheep, goat and sow?
Progesterone production stopped by the corpus luteum or placenta
What determines the timing of onset of parturition in the cow, sheep, goat and sow?
Foetal pituitary-adrenal axis
What does foetal stress lead to in the cow, sheep, goat and sow?
Rise in foetal ACTH
Induces increase in cortisol
What does a rise in foetal cortisol lead to in farm animals?
Increased oestrogen:progesterone ratio
What is flushing?
Rising plane of nutrition before mating in farm animals
How does flushing work?
High energy intake lowers oestradiol concentrations
Promotes FSH release
What does immunisation against androstenedione cause in farm animals?
Removes negative feedback effect on hypothalamus and pituitary
What does immunisation against GnRH cause in farm animals?
Inhibits production of gonadotrophins and gonadal steroids
Reduces testicular size and function
Control aggressionand reduce male-associated odours
What is the dominant hormone in the follicular phase of the oestrus cycle? Luteal phase?
Oestrogen in follicular phase
Progesterone in luteal phase
What is the dominant hormone in each stage of the oestrus cycle based on vaginal cytology?
Pro-oestrus - oestrogen
Oestrus - oestrogen
Metoestrus - transitional
Dioestrus - Progesterone
What is the difference between the bitch and queen in regards to reproductive physiology?
Bitch - mono-oestrus, non-seasonal, polytocous, spontaneous ovulator
Queen - seasonally polyoestrus, polytocous, induced ovulator
What is follicular development regulated by in the bitch?
FSH and LH
Act to synthesise oestradiol
What is LH and FSH secretion regulated by in the bitch?
GnRH from the hypothalamus
Steroids from the ovaries
When does the bitch ovulate?
Spontaneously at the end of a variable follicular phase
What is the length of each stage of the bitches oestrus cycle?
Anoestrus - more than 90 days
Proestrus - 9 days
Estrus - 9 days
Pregnancy/diestrus - 60 days
Describe the endocrine events that occur with LH in the follicular phase in the bitch
Mid/late anestrus - low LH levels, <1 ng/ml, occasional LH pulses
1 week before proestrus - frequency increases with pulses, occur every 60-90 minutes, levels also increase
Proestrus - LH levels become lower, pulses become less detectable
Late proestrus - LH reach peak levels, 8-15 ng/ml
Describe the endocrine events that occur with FSH in the follicular phase in the bitch
Mid/late anestrus - FSH levels are high, FSH levels increase throughout anestrus
1 week before proestrus - modest increases in FSH
Proestrus - FSH levels are low
Late proestrus - peak occurs roughly 1 days after LH surge, modest increase in mean level
Describe the endocrine events that occur with oestradiol in the follicular phase in the bitch
Mid/late anestrus - levels remain low
1 week before proestrus - levels remain low
Proestrus - increase throughout proestrus, go from roughly 10 pg/ml to 120 pg/ml
Late proestrus - peak levels are reached 1-3 days before LH surge
Diestrus - some secretion og oestradiol
What can be a good measure of impending ovulation in the bitch?
Progesterone measurement
Describe the endocrine events that occur with progesterone in the follicular phase in the bitch
Mid/late anestrus - progesterone levels are low
1 week before prosestrus - levels remain low
Proestrus - levels increase slowly, 0.2 to 0.8 ng/ml
Late proestrus - 2-4 ng/ml at time of LH surge, 4-10 ng/ml at time of ovulation
Diestrus - peak values of 15-90 ng/ml are reached post ovulation
When does the LH surge occur in the bitch?
Immediately after peak levels of oestradiol
When does estrus sex behaviour occur in the bitch?
Immediately after peak in oestradiol
What are both LH surge and sex behaviour suggested to be initiated by in the bitch?
Decrease in oestrogen:progesterone ratio
When does ovulation occur in the bitch?
Roughly 2 days after LH surge
Oocytes are immature
What could be the signal for completion of 1st meiotic division in the bitch?
Rising levels of progesterone
What happens to progesterone during the luteal phase in the bitch?
Increases and plateaus
Declines rapidly at luteolysis
What is the only source of progesterone during pregnancy in the bitch?
Corpora lutea
Describe the endocrine events that occur in the luteal phase in the bitch
LH - regulates progesterone secretion, GnRH agonist leads to luteolysis, GnRH antagonist leads to luteolysis
Progesterone - regulates CL’s ability to secrete progesterone, PR antagonist causes luteolysis, inhibits luteal PGF2alpha secretion, inhibits PGF-R
PRL - regulates progesterone secretion from day 25
What does premature luteolysis result in?
Early abortion
How can luteolysis be induced in the bitch?
PGF2alpha at high doses Progesterone receptor antagonist GnRH antagonist Continuous GnRH agonist PRL lowering doses of dopmine agonist
What is essential for the onset of parturition in pregnant bitches?
Rapid pre-partum luteolysis due to feto-placental PGF2alpha release
Describe prolactin endocrine events in the bitch
Pregnant bitches levels of PRL are 4x greater than in non-pregnant animals
Blocking PRL release causes functional demise of the CL and abortion
Pseudopregnancy clinical signs are associated with an increase in PRL levels
When are circulating levels of relaxin elevated in the bitch?
21-24 days after the LH surge
What is the sole source of relaxin in the bitch?
Placenta
Reaches 5 ng/ml in late pregnancy
What is the only specific, pregnancy associated protein identified in the dog?
Relaxin
What is increase in relaxin coincidental with?
Rise in PRL
Why is not practically possible to use progesterone to control oestrus in the bitch?
Not active orally
Short duration of action when given parenterally
What do first generation progestagens have a problem with when using to control oestrus in the bitch?
Inducing GH secretion
Leads to increased risk of acromegaly, mammary tumours and diabetes mellitus
What is a synthetic progestagen designed for oestrus prevention in queens and bitches?
Proligestone
Why is proligestone particularly suitable for controlling oestrus in companion animals?
Strongly anti-gonadotrophic
Weakly progestagenic
Antioestrogenic
What is the disadvantage of using testosterone to control osestrus in bitches?
Affects subsequent fertility
Causes protrusion of clitoris
Enlarges vulva
What is normal in bitches showing clinical signs of pseudopregnancy?
Duration of luteal phase
Concentrations of progesterone
When do non-pregnant bitches exhibit signs of pseudopregnancy?
45 days after the end of oestrus
What are the clinical signs of pseudopregnancy in the bitch?
Weight gain
Mammary development
Occasional lactation
What behavioural changes can bitches exhibit in pseudopregnancy?
Nest making
Nursing of inanimate objects
False parturition
What are the clinical signs of pseudopregnancy associated with in bitches?
Rise in plasma PRL
Noted 6 weeks after the end of oestrus
What usually potentiates the development of pseudopregnancy in bitches?
Any event leading to fall in progesterone
What is the treatment for pseudopregnancy in bitches?
Synthetic progestagens to suppress PRL release
Oestrogens and androgens in combination
Dopamine agonists to inhibit PRL release
What phase of the oestrus cycle do queens not have?
Proestrus
What occurs with oestradiol in the follicular phase in the queen?
Concentrations are relatively high but variable
What occurs with LH upon copulation in the queen?
Rapid release from pituitary
Multiple copulations required to produce sufficient LH to induce ovulation
Describe progesterone events in the queen
Stay at baseline levels till after LH surge
Increase with ovulation and peak after 30 days
Non-pregnant animal the levels decrease
In pregnant levels maintained for a further 25-28 days
Queens that have ovulated don’t return to oestrus until progesterone levels return to baseline
What changes in PRL levels occur in the queen?
Elevated for the last 20 days of pregnancy
Elevated throughout lactation
No changes in PRL in pseudopregnancy
What is the approximate length of the interoestrus interval in the queen?
21 days
What may the interoestrus interval be a useful guide to in the queen?
Whether ovulation or conception has failed to occur
How long is the interoestrus interval of queens that ovulate but don’t conceive?
Roughly 50 days
How long is the luteal phase of mated queens that become pregnant?
Roughly 65 days
What is described as pseudopregnancy in the queen?
Non-pregnant luteal phase
When can pseudopregnancy occur in the queen?
After mating
After spontaneous ovulation
What are the clinical signs of pseudopregnancy in the queen?
Absence of oestrus
How can hCG be used to control oestrus in the queen?
Induces ovulation
Delays subsequent calling
Induces false pregnancy
How can androgens be used to control oestrus in the queen?
Postpone calling
Induces masculinization
Give daily oral doses roughly 30 days before oestrus
How can progesterone be used to control oestrus in the queen?
Prevention - give as soon as calling, suppress call, prevents conception
Temporary postponement - give during anoestrus, postpone what follows
Permanent postponement - repeat doses during anoestrus
