Non-Surgical Population Control

Question 1

Where is GnRH secreted and what is its purpose?

Answer 1

(Released from the hypothalamus and causes gonadotropin (LH and FSH) secretion)

Question 2

During which phase is FSH dominant and what is its purpose?

Answer 2

(Dominant during follicular phase, purpose is to grow follicles)

Question 3

Estrogen has a negative feedback on the hypothalamus and pituitary which affects which two other hormones?

Answer 3

(GnRH and FSH, decreases their secretion)

Question 4

During which phase is progesterone dominant?

Answer 4

(Luteal phase)

Question 5

Megestrol acetate (MGA) is a synthetic form of what hormone?

Answer 5

(Progesterone)

Question 6

Megestrol acetate needs to be started how long before expected proestrus at a minimum to appropriately skip the expected cycle in a dog that is in anestrus?

Answer 6

(MGA needs to be started a minimum of 1 week prior to proestrus and is then given for 32 days → goal is to stop or prevent follicular development by prevent the bitch from going into proestrus)

Question 7

If an owner messed up when they suspected their dog was going to go into proestrus and so they were unable to start MGA prior to their dog going into proestrus, how many days into proestrus can MGA be given?

Answer 7

(Within the first 3 days of proestrus, given for 8 days, will still attract males until clinical signs of proestrus are gone)

Question 8

What is the mechanism of action of megestrol acetate?

Answer 8

(Since it is a progestin, it will have negative feedback on the HPO axis therefore reducing the amount of GnRH, FSH, and LH in the body)

Question 9

When should megestrol acetate not be used?

Answer 9

(Prior to pubertal heat, for more than two consecutive cycles (risk of CEH +/- pyometra if used more), if there is reproductive tissue disease, liver disease, or in pregnant or older bitches)

Question 10

Mibolerone (a synthetic weak androgen) has what effect on the HPO axis?

Answer 10

(Suppresses HPO axis through negative feedback on the hypothalamus)

Question 11

Mibolerone should not be used for any longer than how many years and not used at all in which breed?

Answer 11

(Should not be used for any longer than 2 year and not used in Bedlington terriers)

Question 12

What is the mechanism of action for deslorelin?

Answer 12

(Deslorelin is a GnRH superagonist so it desensitizes and downregulates the gonadotropin receptors in the pituitary which decreases secretion of FSH and LH)

Question 13

What are some of the side effects of deslorelin implants that are particularly more common in older bitches?

Answer 13

(Persistent heat, CEH, and pyometra)

Question 14

What type of drug is cabergoline and what are the suspected mechanisms of actions that make it useful for induction of heat cycles in bitches?

Answer 14

(Cabergoline is a dopamine agonist that is thought to either increase FSH concentrations to help folliculogenesis (not sure how, weren’t given a reason) or stimulate GnRH by blocking prolactins negative feedback on the hypothalamus)

Question 15

What are the side effects of cabergoline?

Answer 15

(Nausea, vomiting, ant coat color change)

Question 16

Deslorelin implants can be used for both preventing and triggering estrus, how are they used to trigger estrus?

Answer 16

(Once an animal with the implant starts to show signs of estrus, you remove the implant so you don’t reach the point where the pituitary gland becomes desensitized to GnRH and estrus can occur normally, if you leave it in too long it will suppress their cycle)

Question 17

Use of a deslorelin implant is associated with ovulation in 75% of cases it is used in and one of the possible issues is an anovulatory heat cycle, how can this risk be minimized?

Answer 17

(By using the implant at least 4-4.5 months after the last cycle the bitch has and avoided using it in early anestrus (the uterus will not be ready for ovulation), if you wait until the body is more primed (so later in anestrus), she is more likely to respond the way you want her to)

Question 18

(T/F) The corpus luteum that is produced by using a deslorelin implant is just as hardy as a CL formed naturally by the body.

Answer 18

(F, they are not as hardy and can sometimes fail to function for the whole diestrus which can translate to pregnancy failure)

Question 19

What is the mechanism of action of aglepristone aka alizin?

Answer 19

(It is a progesterone receptor antagonist so it will complete with progesterone for progesterone receptors → progesterone levels will decline over time and CLs will fail to function)

Question 20

What is the mechanism of action of prostaglandins such a dinoprost?

Answer 20

(Causes luteolysis, smooth muscle contraction (both throughout the body and in the uterus), and opening of the cervix (why it is useful for medical tx of pyos))

Question 21

In which breeds should the use of prostaglandins, especially natural prostaglandins, be avoided because of the side effects (tachypnea, tachycardia, GI upset, drooling, colic like signs)?

Answer 21

(Brachycephalics)

Question 22

How does cabergoline work to prevent pregnancy though it is always combined with other medications because it is too weak to achieve prevention alone?

Answer 22

(It reduces prolactin which is the main luteotropic hormone in the second half of pregnancy so the CL will not longer be supported and there will also be reduced progesterone production (which you can track with bloodwork))

Question 23

What type of drug can be used in cats to suppress estrus by taking advantage of them being long day breeders?

Answer 23

(Melatonin implants, can make their body think its short day still, can also try light therapy (works for both prevention and induction))

Question 24

What are the benefits to allowing cats to have an anestrus cycle for a few months if using light therapy to induce them to be in estrus?

Answer 24

(If you use light therapy to keep them in estrus for a long time, you will see a decline in fertility so if you give them a break, you will see better fertility and better litter sizes)

Question 25

(T/F) Use of a GnRH agonist for chemical castration in male dogs is a temporary, reversible suppression of testicular function.

Answer 25

(T)

Question 26

When is the use of GnRH agonists for chemical castration indicated?

Answer 26

(In cases of benign prostatic hyperplasia and/or testosterone related behavioral issues in which the dogs cannot be neutered)

Question 27

How long can it take to restore the fertility of a dog who was chemically castrated with a GnRH agonist?

Answer 27

(6-7 months, check a BSE prior to trying to breed)

Question 28

The anestrus period is a minimum of what months in dogs?

Answer 28

(4 months → allows for appropriate level of repair (involution, desquamation of endometrium, etc.) to occur in the uterus after completion of a heat cycle)