Pharmacological control of reproduction

Question 1

Fill in the female reproductive control diagram

Answer 1

Question 2

What can be used to suppress cycle in females?

Answer 2

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

Question 3

What does FSH trigger in females & males?

Answer 3

Females: follicle development
Males: spermatogenesis

Question 4

Fill in the male reproductive control diagram

Answer 4

Question 5

What is the primary negative feedback mechanism controlling male reproduction?

Answer 5

Testosterone (from Leydig cells) inhibits GnRH release from hypothalamus & LH/FSH release from pituitary

Question 6

What happens when exogenous androgens (e.g. testosterone injections) are given to males?

Answer 6

They suppress GnRH, LH & FSH production, leading to reduced testicular function & sperm production

Question 7

What are the effects of administering progestogens to males?

Answer 7

Decrease testosterone levels
Suppress spermatogenesis
Reduce libido

Question 8

Why are oestrogens not commonly used for hormonal control?

Answer 8

They can cause bone marrow suppression, anaemia & thrombocytopenia

Question 9

What is “Durateston,” and why does its use affect testicle size?

Answer 9

Durateston is testosterone depot that suppresses endogenous testosterone production via negative feedback, leading to testicular atrophy

Question 10

Why are male dogs with perianal adenoma treated with a depot progestogen (Delvosteron)?

Answer 10

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)

Question 11

Why can male dogs with high libido be given a GnRH agonist (Deslorelin, Suprelorin)?

Answer 11

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)

Question 12

How can hormonal testing confirm the presence of testicular tissue in a cryptorchid animal?

Answer 12

hCG (LH-like hormone) or GnRH stimulation test

If functional testicular tissue is present, testosterone levels will rise post-injection

Question 13

Can giving exogenous LH, FSH, or GnRH improve semen quality in males?

Answer 13

No, because natural hormone pulses regulate sperm production & we can’t mimic this rhythm artificially

Question 14

What are the common reasons for hormonal control of female reproduction?

Answer 14

Stimulation of the HPO axis

Control of oestrus/ovulation

Resolution of ovarian pathology

Treatment of pseudopregnancy/termination of pregnancy

Parturition and lactation

Question 15

What are the main methods for controlling oestrus and ovulation?

Answer 15

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

Question 15

Why might we want to control oestrus and ovulation in animals?

Answer 15

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

Question 16

How can gonadotropins be used in oestrus control?

Answer 16

Stimulation – Administer GnRH to induce ovulation

Suppression – Long-term GnRH agonists for reproductive downregulation

Question 17

How can oestrus be stimulated earlier in sheep?

Answer 17

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

Question 18

Why is synchronising oestrus in sheep useful?

Answer 18

It synchronises lambing, making management easier & ensuring staff are available to assist at right time

Question 19

What are the main hormonal protocols used to control oestrus in cows?

Answer 19

Ovsynch (with or without P4)

Progestogen + PGF

2 doses of PGF ~12 days apart

Question 20

Why are two doses of PGF ineffective for oestrus synchronisation in pigs?

Answer 20

Because corpus luteum in pigs is not consistently responsive to PGF like it is in cattle

Question 21

How is oestrus synchronisation used in pigs?

Answer 21

Progestogen (oral) for 14-18 days ± ECG before P4 removal – used for batch farrowing

Limited hormonal use after weaning – pigs typically resume cycling naturally

Question 22

Why is progesterone used in hormonal protocols for cattle?

Answer 22

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

Question 23

What is the P4 + PGF protocol for oestrus synchronisation in cattle?

Answer 23

1. Insert PRID or CIDR (progesterone device)
2. Leave for 7-9 days
3. 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
4. Remove PRID/CIDR
5. AI at 56 hours (single AI) or perform double AI.

Question 24

What is the Ovsynch protocol in cattle?

Answer 24

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

Question 25

How can progesterone be incorporated into the Ovsynch protocol?

Answer 25

Progesterone device (PRID/CIDR) can be added after first GnRH injection Ensures sufficient progesterone levels before luteolysis Leads to more predictable ovulation & improves synchronisation

Question 26

What are the main approaches to controlling oestrus in companion animals?

Answer 26

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

Question 27

How can oestrus be suppressed in horses for training and performance?

Answer 27

Repeated progestogen treatments for 10-15 days prevent cycling

Question 28

How can cyclicity be stimulated in early breeding season in horses?

Answer 28

Increasing daylight exposure (most common method) Oral progestogen for ~10 days to mimic luteal phase

Question 29

What hormonal treatments help manage AI/mating in horses?

Answer 29

Progestogen – Used to regulate cycling PGF2α – If active CL is present, it induces luteolysis HCG or GnRH – To hasten ovulation & improve AI timing

Question 30

What are the methods for preventing or suppressing oestrus in dogs?

Answer 30

Progestogen depots (last 6+ months, but increase pyometra risk if used in pro-oestrus) GnRH agonist implant (takes time to act) Testosterone (Greyhounds)

Question 31

When would we induce oestrus in dogs and how?

Answer 31

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

Question 32

What methods are used for preventing or suppressing oestrus in cats?

Answer 32

GnRH agonist implants – Long-term suppression GnRH antagonists – Short-term suppression Melatonin implants – Alters seasonality

Question 33

How can oestrus be induced in cats?

Answer 33

Increased daylight exposure – Stimulates natural cycling HCG injection – Induces ovulation

Question 34

What is anovulatory anoestrus in cattle?

Answer 34

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

Question 35

What factors contribute to anovulatory anoestrus?

Answer 35

Nutritional state – Energy balance & body condition Lactation stage – High milk production can delay return to cyclicity Hormonal imbalances – Lack of gonadotropin stimulation

Question 36

What are the main treatment goals for anovulatory anoestrus?

Answer 36

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

Question 37

How does the Ovsynch protocol help treat anovulatory anoestrus?

Answer 37

Ovsynch = GnRH → PGF2α → GnRH First GnRH → Induces follicular growth or ovulation PGF2α → Lyses CL (if present) Second GnRH → Induces ovulation

Question 38

What modifications to Ovsynch improve treatment success for anovulatory anoestrus?

Answer 38

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

Question 39

What is Cystic Ovarian Disease (COD) in cattle?

Answer 39

Condition where follicular structures persist longer than normal Can be follicular or luteal cysts Leads to irregular or absent oestrus, affecting fertility

Question 40

Why is diagnosis of COD challenging?

Answer 40

Difficult to differentiate between follicular & luteal cysts Progesterone testing useful—high progesterone suggests luteal cyst Monitoring over time improves accuracy

Question 41

What are the key principles of treating COD?

Answer 41

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

Question 42

How are follicular cysts treated?

Answer 42

GnRH to induce luteinisation, followed by PGF2α (e.g. Ovsynch protocol) Progestogen-based therapy to suppress gonadotropins & reset cycle

Question 43

How are luteal cysts treated?

Answer 43

PGF2α to induce luteolysis & regression of cyst

Question 44

What is a persistent corpus luteum (CL)?

Answer 44

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

Question 45

What causes a persistent CL?

Answer 45

Lack of endometrial PGF2α production, preventing normal luteolysis Pregnancy must be ruled out before treatment, as prolonged CL is normal in pregnancy

Question 46

What is the treatment for a persistent CL?

Answer 46

PGF2α injection to induce luteolysis Cows should return to oestrus within 2-5 days

Question 47

What is immuno-contraception?

Answer 47

Vaccine-based method to prevent reproduction in animals Targets key reproductive proteins to block fertility Aimed at reducing need for surgical sterilisation

Question 48

What are the two main types of immuno-contraception vaccines?

Answer 48

Zona Pellucida Vaccines – Prevents fertilisation Anti-GnRH Vaccines – Suppresses reproductive hormone production

Question 49

How do Zona Pellucida (ZP) vaccines work?

Answer 49

Targets ZP proteins surrounding the oocyte Prevents sperm from binding, blocking fertilisation

Question 50

How do Anti-GnRH vaccines work?

Answer 50

Induce immune response against GnRH Prevents release of LH & FSH, suppressing fertility

Question 51

What is pseudopregnancy in dogs?

Answer 51

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

Question 52

What are the treatment options for pseudopregnancy?

Answer 52

Prolactin inhibitors – Reduce prolactin levels, stopping symptoms PGF2α (Prostaglandins) – Induce luteolysis but have significant side effects in dogs, so not commonly used

Question 53

What drugs are used for early pregnancy termination in dogs and cats?

Answer 53

Progesterone receptor antagonists – Block progesterone, preventing pregnancy maintenance

Question 54

What drugs are used for late-stage pregnancy termination?

Answer 54

Corticosteroids – Mimic fetal stress signals to induce parturition PGF2α (Prostaglandins) – Cause luteolysis & uterine contractions (often combined with corticosteroids)