Pharmacological control of reproduction Flashcards
Fill in the female reproductive control diagram
What can be used to suppress cycle in females?
Progesterone (but would cause mammary gland development)
Testosterone (not widely used)
Oestrogen (but has effect on bone marrow)
GnRH
All would cause a negative feedback effect
What does FSH trigger in females & males?
Females: follicle development
Males: spermatogenesis
Fill in the male reproductive control diagram
What is the primary negative feedback mechanism controlling male reproduction?
Testosterone (from Leydig cells) inhibits GnRH release from hypothalamus & LH/FSH release from pituitary
What happens when exogenous androgens (e.g. testosterone injections) are given to males?
They suppress GnRH, LH & FSH production, leading to reduced testicular function & sperm production
What are the effects of administering progestogens to males?
Decrease testosterone levels
Suppress spermatogenesis
Reduce libido
Why are oestrogens not commonly used for hormonal control?
They can cause bone marrow suppression, anaemia & thrombocytopenia
What is “Durateston,” and why does its use affect testicle size?
Durateston is testosterone depot that suppresses endogenous testosterone production via negative feedback, leading to testicular atrophy
Why are male dogs with perianal adenoma treated with a depot progestogen (Delvosteron)?
Perianal adenomas are testosterone-dependent, so reducing testosterone levels (via negative feedback loop) shrinks tumour
(Wouldn’t use androgen (testosterone) in this situation, as this would stimulate anal adenoma despite endogenous testosterone falling)
Why can male dogs with high libido be given a GnRH agonist (Deslorelin, Suprelorin)?
Despite initial stimulation of GnRH receptors it would lead to down-regulation of receptors with prolonged use –> temporary suppression of testosterone & spermatogenesis & thus libido
(so they actually act as GnRH antagonists)
How can hormonal testing confirm the presence of testicular tissue in a cryptorchid animal?
hCG (LH-like hormone) or GnRH stimulation test
If functional testicular tissue is present, testosterone levels will rise post-injection
Can giving exogenous LH, FSH, or GnRH improve semen quality in males?
No, because natural hormone pulses regulate sperm production & we can’t mimic this rhythm artificially
What are the common reasons for hormonal control of female reproduction?
Stimulation of the HPO axis
Control of oestrus/ovulation
Resolution of ovarian pathology
Treatment of pseudopregnancy/termination of pregnancy
Parturition and lactation
What are the main methods for controlling oestrus and ovulation?
Influencing photoperiod – manipulating light exposure for seasonal breeders
Mimicking gonadotropin release – GnRH for stimulation or suppression
Modifying luteal phase:
- Lengthen/mimic – maintain pregnancy-like state
- Block progesterone – disrupt luteal function
- Shorten luteal phase – PGF2α or prolactin inhibitors to return to oestrus faster
Why might we want to control oestrus and ovulation in animals?
Induce ovulation – precisely time mating or AI
Hasten return to cyclicity – after parturition or seasonal anoestrus
Synchronize breeding – e.g. ewes bred in August/September instead of October/November
Prevent breeding – esp. in companion animals
How can gonadotropins be used in oestrus control?
Stimulation – Administer GnRH to induce ovulation
Suppression – Long-term GnRH agonists for reproductive downregulation
How can oestrus be stimulated earlier in sheep?
Melatonin – stimulates GnRH release & early resumption of HPO axis activity
Progestogen sponges + ECG/GnRH – mimics luteal phase, resets cycle & induces cycling upon removal
Ram effect – induces oestrus earlier when introduced to females
Why is synchronising oestrus in sheep useful?
It synchronises lambing, making management easier & ensuring staff are available to assist at right time
What are the main hormonal protocols used to control oestrus in cows?
Ovsynch (with or without P4)
Progestogen + PGF
2 doses of PGF ~12 days apart
Why are two doses of PGF ineffective for oestrus synchronisation in pigs?
Because corpus luteum in pigs is not consistently responsive to PGF like it is in cattle
How is oestrus synchronisation used in pigs?
Progestogen (oral) for 14-18 days ± ECG before P4 removal – used for batch farrowing
Limited hormonal use after weaning – pigs typically resume cycling naturally
Why is progesterone used in hormonal protocols for cattle?
Maintains luteal phase & prevents early ovulation
Needs to be administered for at least 7 days (often 7-14 days)
Upon removal, rapid progesterone drop triggers follicular phase
What is the P4 + PGF protocol for oestrus synchronisation in cattle?
- Insert PRID or CIDR (progesterone device)
- Leave for 7-9 days
- Administer PGF2α at least 24 hours before removal
- Ensures any residual luteal tissue is lysed
- Allows for rapid progesterone drop, which is crucial for oestrus induction - Remove PRID/CIDR
- AI at 56 hours (single AI) or perform double AI.
What is the Ovsynch protocol in cattle?
Day 0 – GnRH injection (induces new follicle growth)
Day 7 – PGF2α injection (causes luteolysis)
50-60 hours later – 2nd GnRH injection (induces ovulation)
16-20 hours later – Fixed-time AI
How can progesterone be incorporated into the Ovsynch protocol?
Progesterone device (PRID/CIDR) can be added after first GnRH injection
Ensures sufficient progesterone levels before luteolysis
Leads to more predictable ovulation & improves synchronisation
What are the main approaches to controlling oestrus in companion animals?
Prevention of oestrus – Stop heat cycles before they begin
Suppression of oestrus – Temporarily halt reproductive activity
Induction of oestrus – Used when oestrus is delayed or absent due to an issue
How can oestrus be suppressed in horses for training and performance?
Repeated progestogen treatments for 10-15 days prevent cycling
How can cyclicity be stimulated in early breeding season in horses?
Increasing daylight exposure (most common method)
Oral progestogen for ~10 days to mimic luteal phase
What hormonal treatments help manage AI/mating in horses?
Progestogen – Used to regulate cycling
PGF2α – If active CL is present, it induces luteolysis
HCG or GnRH – To hasten ovulation & improve AI timing
What are the methods for preventing or suppressing oestrus in dogs?
Progestogen depots (last 6+ months, but increase pyometra risk if used in pro-oestrus)
GnRH agonist implant (takes time to act)
Testosterone (Greyhounds)
When would we induce oestrus in dogs and how?
Only in cases of delayed puberty or prolonged lactational anoestrus
Methods:
- Prolactin inhibitors (2-5 weeks) – Removes prolactin’s inhibitory effect
- GnRH agonist implant – Stimulates FSH/LH release
- HCG – Directly induces ovulation
What methods are used for preventing or suppressing oestrus in cats?
GnRH agonist implants – Long-term suppression
GnRH antagonists – Short-term suppression
Melatonin implants – Alters seasonality
How can oestrus be induced in cats?
Increased daylight exposure – Stimulates natural cycling
HCG injection – Induces ovulation
What is anovulatory anoestrus in cattle?
Condition where ovaries lack follicles or functional CL
Ovaries appear small with no active structures
Leads to delayed or absent oestrus, affecting fertility & calving intervals
What factors contribute to anovulatory anoestrus?
Nutritional state – Energy balance & body condition
Lactation stage – High milk production can delay return to cyclicity
Hormonal imbalances – Lack of gonadotropin stimulation
What are the main treatment goals for anovulatory anoestrus?
Ensure animals are in breeding window for timely conception
Stimulate follicular development to ensure mature ovulatory follicle
Control ovulation timing for fixed-time AI
Ensure induced CL is functionally normal
How does the Ovsynch protocol help treat anovulatory anoestrus?
Ovsynch = GnRH → PGF2α → GnRH
First GnRH → Induces follicular growth or ovulation
PGF2α → Lyses CL (if present)
Second GnRH → Induces ovulation
What modifications to Ovsynch improve treatment success for anovulatory anoestrus?
Ovsynch + Progestogen – Ensures controlled luteal phase before ovulation induction
Progesterone + eCG
- Progesterone → Mimics luteal phase, resets cycle
- eCG (low dose) → Stimulates FSH-like activity, enhancing follicular growth
What is Cystic Ovarian Disease (COD) in cattle?
Condition where follicular structures persist longer than normal
Can be follicular or luteal cysts
Leads to irregular or absent oestrus, affecting fertility
Why is diagnosis of COD challenging?
Difficult to differentiate between follicular & luteal cysts
Progesterone testing useful—high progesterone suggests luteal cyst
Monitoring over time improves accuracy
What are the key principles of treating COD?
Resolve predisposing factors – Otherwise, new cysts may form
Accurate diagnosis is critical – Misdiagnosis can lead to ineffective treatment
Luteinise follicular structures if present
Suppress hypothalamus-pituitary axis to stop gonadotropin stimulation
Stimulate luteolysis if luteal tissue is present
How are follicular cysts treated?
GnRH to induce luteinisation, followed by PGF2α (e.g. Ovsynch protocol)
Progestogen-based therapy to suppress gonadotropins & reset cycle
How are luteal cysts treated?
PGF2α to induce luteolysis & regression of cyst
What is a persistent corpus luteum (CL)?
CL that remains beyond normal luteal phase, delaying oestrus
Difficult to diagnose – Looks identical to normal CL on ultrasound
Requires history & clinical signs for diagnosis
What causes a persistent CL?
Lack of endometrial PGF2α production, preventing normal luteolysis
Pregnancy must be ruled out before treatment, as prolonged CL is normal in pregnancy
What is the treatment for a persistent CL?
PGF2α injection to induce luteolysis
Cows should return to oestrus within 2-5 days
What is immuno-contraception?
Vaccine-based method to prevent reproduction in animals
Targets key reproductive proteins to block fertility
Aimed at reducing need for surgical sterilisation
What are the two main types of immuno-contraception vaccines?
Zona Pellucida Vaccines – Prevents fertilisation
Anti-GnRH Vaccines – Suppresses reproductive hormone production
How do Zona Pellucida (ZP) vaccines work?
Targets ZP proteins surrounding the oocyte
Prevents sperm from binding, blocking fertilisation
How do Anti-GnRH vaccines work?
Induce immune response against GnRH
Prevents release of LH & FSH, suppressing fertility
What is pseudopregnancy in dogs?
Physiological condition where non-pregnant female shows pregnancy-like signs
Due to hormonal changes after oestrus, even without mating
Most cases don’t require treatment unless signs are severe
What are the treatment options for pseudopregnancy?
Prolactin inhibitors – Reduce prolactin levels, stopping symptoms
PGF2α (Prostaglandins) – Induce luteolysis but have significant side effects in dogs, so not commonly used
What drugs are used for early pregnancy termination in dogs and cats?
Progesterone receptor antagonists – Block progesterone, preventing pregnancy maintenance
What drugs are used for late-stage pregnancy termination?
Corticosteroids – Mimic fetal stress signals to induce parturition
PGF2α (Prostaglandins) – Cause luteolysis & uterine contractions (often combined with corticosteroids)
