Sex hormones

By | 2011-08-18

Oestrogens

Oestrogens are responsible physiologically for initiating behavioural signs of oestrus, preparing the female reproductive tract for fertilisation and developing the secretory tissue of the mammary gland. They also have anabolic activity.

Oestrogens are used in the treatment of misalliance in the bitch. They act by inhibiting the transport of the fertilised ova down the oviducts, in addition to causing hypertrophy of the uterine mucosa. Urinary incontinence in the spayed bitch may also be controlled with oestrogens.

In males, oestrogens are used in the treatment of excess libido, anal adenoma, and, with caution, for prostate hyperplasia.

The use of stilbenes, such as diethylstilbestrol (with the following exception), is prohibited in food-producing animals because they have been found to be carcinogenic in humans under some circumstances. Administration is allowed, if prior steps are taken to ensure that the treated animal and its products are not available for human or animal consumption. This exemption allows the administration of authorised-human products to farm animals for research purposes and also to companion and laboratory animals. Oestrogens may cause aplastic anaemia in dogs and cats and cystic endometrial hyperplasia in bitches. Overdosage can cause severe inhibition of pituitary function and cystic ovaries, particularly in cattle and pigs; repeated administration to treat misalliancee can cause coagulopathy in bitches.

DIETHYLSTILBESTROL

(Stilboestrol)

Indications. See under Dose; urinary incontinence; behavioural modification

Contra-indications. See notes above

Warnings. Overdosage may cause severe inhibition of pituitary function, anaemia and thrombocytopenia, squamous metaplasia of the prostate, cystic endometrial hyperplasia

Dose:

Dogs: prostatic hyperplasia, anal adenoma, by mouth, up to 1 mg daily, reducing to maintenance dose

Prescription-only medicine: © Diethylstilbestrol (Non-proprietary) UK

Tablets, diethylstilbestrol 1 mg, 5 mg

ESTRADIOL

(Oestradiol)

Indications. See Dose under preparation details; urinary incontinence

Contra-indications. Cats

Warnings. Oestrogens, particularly if used repeatedly, may cause aplastic anaemia, coagulopathies, increased risk of cystic endometrial hyperplasia, and pyometra in bitches; owners should be warned that pregnancy may not be terminated in 5% of treated bitches

Dose:

Dogs: misalliance, by subcutaneous or intramuscular injection, 10 micrograms/kg administered on day 3, day 5, and (if required) day 7 after mating

Prescription-only medicine: Mesalin (Intervet) UK

Injection (oily), estradiol benzoate 200 micrograms/mL, for dogs

ETHINYLESTRADIOL

(Ethinyloestradiol)

Indications. See notes above and under Dose

Side-effects. Feminisation

Warnings. Overdosage may cause severe inhibition of pituitary function, anaemia and thrombocytopenia, squamous metaplasia of the prostate, cystic endometrial hyperplasia

Dose: By mouth.

Dogs. Males: prostatic hyperplasia, anal adenoma, 50-100 micrograms daily. If feminisation occurs, cease treatment. Recommence therapy at half original dose

Prescription-only medicine: @ Ethinylestradiol (Non-proprietary) UK

Tablets, ethinylestradiol 10 micrograms, 50 micrograms, 1 mg

Progestogens

Antiprogestogens

Antiprogestogens are used to terminate pregnancy in bitches. They act in a number of different ways. Dopamine receptor agonists, such as bromocriptine and cabergoline exert their effect by reducing prolactin levels, and hence progesterone secretion by the corpora lutea. Some enzyme inhibitors such as epostane prevent the conversion of pregnenolone to progesterone. Both these groups reduce plasma-progesterone concentration, which is necessary for the maintenance of pregnancy. Aglepristone is a progesterone receptor antagonist, which blocks the effect of progesterone on the target tissues; progesterone concentrations in the peripheral circulation are not affected. Aglepristone is used to terminate pregnancy in bitches up to 45 days after mating. Termination of pregnancy should be confirmed by examination of animals 10 days after treatment and at least 30 days after mating. A partial abortion may occur in some bitches with retention of one or more puppies, which may become macerated. In animals treated after day 20 of gestation, abortion is accompagnied by physiological signs of parturition such as fetal expulsion, slight anorexia, and mammary congestion. An early return to oestrus is seen in animals treated with aglepristone with the oestrus to oestrus interval being shortened by one to three months.

AGLEPRISTONE

Indications. Pregnancy termination in bitches

Contra-indications. Hypersensitivity to aglepristone

Side-effects. Transient pain at injection site

Warnings. Owners should be warned that partial abortion may occur in 5% of bitches; early return to oestrus after treatment; physiological signs of parturition seen in bitches treated after day 20 of gestation; may cause abortion in humans and women should take care to avoid accidental self-injection

Dose:

Dogs: by subcutaneous injection, 10 mg/kg. Repeat after 24 hours

Prescription-only medicine: Alizin (Virbac) UK

Injection, (oily), aglepristone 30 mg/mL, for dogs

Accidental self-injection with oil-based injections can cause severe pain and intense swelling, which may result in ischaemic necrosis and loss of a digit. Prompt medical attention is essential. A copy of the warning given in the package leaflet or data sheet should be shown to the doctor (or nurse) on duty.

Androgens

Compound hormonal preparations

A combination of hormones is used to induce a preseasonal ovulation, synchronise oestrus in a group of animals, or enable prediction of the time of oestrus. Some compound preparations are also used in the treatment of ovarian cysts or for the control of clinical signs of pseudopregnancy. Their use is unlikely to produce satisfactory results in animals in deep anoestrus, immature animals, animals with genital-tract abnormalities, or when breeding problems have resulted from severe nutritional deficiency or other stresses.

Prescription-only medicine: PG 600 (Intervet) UK

Injection, powder for reconstitution, chorionic gonadotrophin 200 units, serum gonadotrophin 400 units, for pigs more than 5 months of age

Withdrawal Periods.

Pigs: slaughter withdrawal period nil

Contra-indications. Injection into subcutaneous fat

Side-effects. Anaphylactic reactions

Dose: Sows, gilts: anoestrus, suboestrus, by intramuscular injection, 5 mL of reconstituted solution

Sows, post weaning: to promote early postpartum oestrus, by intramuscular injection, 5 mL of reconstituted solution within 2 days of weaning Note. Gilts more than 5 months of age, a single dose normally results in fertile oestrus within 5 days

Prescription-only medicine: Prid (Ceva) UK

Intravaginal device, progesterone 1.55 g, estradiol benzoate 10 mg, for cows, mature heifers

Withdrawal Periods.

Cattle: milk withdrawal period nil

Note. For 24 hours after insertion, animals must not be sent for slaughter and at all times the intravaginal device should be removed at least 6 hours before slaughter

Contra-indications. Immature heifers; cows calved less than 30 days except when using at 21 days onwards for late calving herds where, in healthy cows, early service is required; pregnant cattle; genital tract infections

Dose:

Cattle: anoestrus, suboestrus, synchronisation of oestrus, by intravaginal administration, 1 device. Remove after 12 days, and follow by insemination either 2 times, at 48 hours and 72 hours, or once at 56 hours, after removal. May be used in conjunction with serum gonadotrophin and prostaglandin For analogues