MEDICINAL TERMINATION OF PREGNANCY IN BITCHES

PREPARED BY: Burhan-ud-din Shafi

Mismating also known as misalliance refers to situations in which an animal is bred in contrast to the wishes of the owner.

Unwanted mating or mismating is a common clinical problem in veterinary practice which may arise because dog owners are not aware that their pet is “in heat” or the owner may be aware of estrus but underestimated the will of a stud or bitch that wants to encounter the opposite sex. Therefore, even the best educated and most careful owners will end up with mismating problems in their bitches.

To determine whether mating has indeed occurred is to examine a vaginal smear.

If the dog was bred , one can almost always find sperm on the smear without much difficulty.

We can have the bitch ultra-sound scanned 35-40days after mating.

04/18/23

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MEDICINAL TERMINATION OF PREGNANCY

Modification of estrogen-progesterone ratio by administration of estrogen/synthetic estrogen derivatives /glucocorticoids.

Induction of functional luteal arrest or luteolysis by substances that act directly (prostaglandins) or indirectly on the CL by inhibiting luteotrophic support.

Blockage of progesterone secretion by inhibiting steroidogenesis (epostane)

Blockage of progesterone action at the receptor levels (anti progesterone (mifipristone / algepristone).  

Stage 1: Canine Fertilization to Implantation

Occurs 18 days from the LH

Changes in estrogen:progesterone ratio or decline in corpus luteum progesterone secretion can lead to impaired implantation or abortion.

Drugs used to terminate pregnancy at this stage include:

estrogens: Estradiol benzoate, estradiol valerate

prostaglandins: inhibitors of progesterone secretion (epostane)

progesterone antagonists (mifeprestone, aglepristone).

Stage 2: Implantation to Fetal Ossification

Fetal ossification occurs at 40 to 42 days from the LH peak

Drugs used to terminate pregnancy at this stage include:

prostaglandins,

dopamine agonists/antiprolactinic agents (bromocriptine, cabergoline), antiserotoninergic (methergoline),

steroids (dexamethasone),

progesterone-secretion inhibitors (epostane)

progesterone antagonists (mifeprestone, aglepristone),

Stage 3: Fetal Ossification to Parturition

Prostaglandins reduce corpus luteum blood supply and luteal steroidogenesis. Abortion induction at this stage is likely to result in premature parturition and delivery of live pups.

Administration of Estrogen

• Estrogens exert their action by causing

• closure of the uterotubal junction,

• alter the transport time of zygotes

• exert direct embryotoxic effect resulting in implantation failure or embryonic death.

• Estradiol benzoate

• 0.5-3 mg/kg for one injection within 4 days of mating

• Estradiol valerate@3.0-7 mg once for 3-4 days

Estradiol benzoate @ 0.5 - 3.0 mg every other day for a total of three injections beginning 4 - 10 days after misalliance.

Estradiol valerate @ 3.0 - 7.0 mg administered once 4 to 10 days after mismating.

Contd

Risk after administration of estrogen

Pyometra

Metritis

Ovarian cysts

Aplastic anemia, bone marrow suppression

Alopecia,skin hyperpigmentation

Prolongation of estrus Clinically, > 60% bitches after an unwanted mating are not

pregnant

Prostagladins

Prostaglandins cause lysis of corpora lutea and decrease in plasma concentrations of progesterone.

Prostaglandins also produce contraction of smooth muscle having an ecbolic effect thereby inducing abortion

The bitches must be healthy and less than 7 years of age. Pregnancy must be confirmed using ultrasonography

Corpus luteum of the bitch are highly resistant to prostaglandins than those of other species.

Repeated therapy is necessary to achieve complete regression of the corpus luteum

Dinoprost ( lutalyse) :20-30µg/kg b.i.d for 4-7 day

Cloprostenol@2.5µg/kg for 4-7 days at alternate days

Given after 30 days of pregnancy

Contd:

Side effects

vomiting, diarrhea, pupil dilation, hyperpnoea, salivation, urination, anxiety and ataxia

Side effects can be reduced by concurrent

administration of anticholinergic drugs like atropine @ 0.5 mg/kg SC or IM, 15 minutes before prostaglandin administration

. Walking the animal for 30 minutes following PGF2 α injections would help to reduced intensity of side effects

Dopamine agonist

Prolactin is the major luteotropic hormone throughout the luteal phase in both pregnant and non pregnant bitches

Antiprolactin agents, with strong dopamine D 2 receptor agonist activity, have been used to induce abortion, from 30-40 days after LH surge.

Contd

Bromocriptine@20µg/kg b.i.d for 6 days

Cabergoline(cabgolin , camforte)@5µg/kg once daily for 5 days

PGF2 + Dopamine agonist

A combination therapy of oral cabergoline at 5 µg/kg per day and low dose of cloprostenol (PGF 2 α analogues) injection of 1 µg/kg SC every other day for upto 9 days terminated pregnancy in dogs when administered starting around day 28 of pregnancy.

The regression of the CL is achieved by double mechanism of action, Direct local effect of PG on CL steroidogenesis Indirect effect due to withdrawal of pituitary prolactin

Advantage: safe for the bitch

terminating pregnancy by resorption rather than by abortion

effective as early as 25 days after the 1st mating

All the treated bitches returned in heat and become pregnant and had normal litters. Thus, this treatment did not compromise the fertility of the treated animals.

Progesterone receptor antagonist

Mifepristone@2.5 mg/kg, sc, bid for 5 days after 32 daysMifepristone@2.5 mg/kg, sc, bid for 5 days after 32 daysAglepristone@10 mg/kg, sc, for 2 days 30 days after ovulationAglepristone@10 mg/kg, sc, for 2 days 30 days after ovulation

abortion within 4-7 daysabortion within 4-7 days

CORTICOSTEROIDS:

Dexamethasone when administered beginning at mid gestation can terminate pregnancy in dogs by activating endogenous mechanisms similar to those involved in parturition.

Injectable Dexamethasone (5 mg twice daily IM for 10 days)

oral Dexamethasone (0.1 to 0.2 mg twice daily at a decreasing dose for 5 to 10 days

Side effects: polydipsia , polyuria , vaginal discharge, restlessness, anorexia or vomition

Miscellaneous drugs…

Epostane :

A steroid molecule that inhibits steroid synthesis at the level of the hydroxy steroid – dehydrogenase isomerase enzyme system, thereby inhibiting the formation of progesterone from pregnanolone .

It terminates pregnancy when given orally at 2.5 to 5 mg/kg for 7 days starting any time after diestrus