Human Chorionic Gonadotropin (hCG)

Human chorionic gonadotropin is a glycoprotein hormone with predominantly luteinizing-hormone-like activity. Veterinary therapeutic uses include induction of ovulation and treatment of selected reproductive disorders. It acts directly at gonadal receptors, distinguishing it from GnRH analogues that stimulate pituitary gonadotropin release. Diagnostic gonadal-response testing is a separate application.

Group

Gonadotropin; predominantly LH-like activity

Mechanism of Action

hCG activates luteinizing-hormone receptors in ovarian or testicular tissue. In responsive follicles it promotes final maturation, ovulation and luteinization, followed by luteal progesterone production. In Leydig cells it stimulates testosterone synthesis. These direct gonadal effects explain the therapeutic reproductive response and the hormone changes used in gonadal stimulation testing.

Dose Rates

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Ovarian cysts	10000 IU/animal	IM	Once	Deep IM; may repeat after 14 days if examination indicates persistent disease.
Ovarian cysts	2500–5000 IU/animal	IV	Once	Separate IV alternative; reassess before repeating after 14 days.

Horses

Use / stage	Dose	Route	Schedule	Instructions
Ovulation induction	2000–3000 IU/animal	IV	Once	Mares in early oestrus with a dominant follicle over 35 mm; source suggests treatment about 6 hours before mating.

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Persistent follicular cyst luteinisation	500 IU/animal	IM	Once	May repeat after 48 hours; source anticipates conversion to oestrus in 1-2 days if effective.
Functional ovarian tissue test	100–1000 IU/animal	IM	Once	During apparent oestrus; measure progesterone 5-7 days later. A value above 1 ng/mL supports functional ovarian tissue.
Ovulation failure-associated infertility	500 IU/animal	SC	Once	Next cycle, give on heat days 10-11 or when cytology indicates breeding readiness; breed two days later.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Functional ovarian tissue test	50–100 IU/animal	IM	Once	Queens in apparent oestrus; measure progesterone in 5-7 days.
Confirmed ovulation failure	100–500 IU/animal	IM	Once
Artificial insemination-associated ovulation	50–75 IU/animal	IM	Every 24 h	Give immediately after insemination; repeat insemination and injection once after 24 hours.

Ferrets

Use / stage	Dose	Route	Schedule	Instructions
Persistent oestrus	100 IU/animal	IM	Every 168 h	Repeat in one week only if needed; source reports best response 14 days after oestrus begins.

Guinea pigs

Use / stage	Dose	Route	Schedule	Instructions
Ovarian cysts	1000 IU/animal	IM	Every 168–240 h	Repeat after 7-10 days if required.

Birds

Use / stage	Dose	Route	Schedule	Instructions
Feather-plucking adjunct	500–1000 IU/kg	IM		Empirical use, especially females. Repeat after 3 days only if no response; if two injections fail, further escalation is unlikely to help. Repeated responders may require 4-6 week intervals.

Indications

Treatment of selected bovine follicular ovarian cysts associated with infertility or persistent estrus.
Induction of ovulation in mares with a suitable mature follicle.
Induction of ovulation in selected ferrets with prolonged estrus to address sustained estrogen exposure.
Induction of fertile estrus in selected prepubertal gilts or delayed-return weaned sows when used in a corresponding eCG–hCG combination product.

Contraindications

Hypersensitivity; use cautiously with androgen-dependent neoplasia.
Avoid inappropriate administration in early equine pregnancy.

Interactions

Repeated administration may induce neutralising antibodies and diminish efficacy.

Adverse effects

Hypersensitivity, injection pain and variable ovarian response.
Early pregnancy loss has been reported in mares.

Toxicity

No established veterinary overdose antidote; manage hypersensitivity and reproductive complications.

Preparations

Preparation	Form	Strength	Route
Chorulon 10000 IU vial Vial content only; final mL concentration is not inferred. Reconstitute using the supplied product instructions.	Injection	10000 IU / vial	IM, IV

Monitoring and Administration

Select treatment using cycle stage, follicular size and reproductive examination.

Express potency in IU, not mass: source hCG challenge tests printed in micrograms are not automatically interchangeable with IU-labelled products.

Reconstitute the cited Chorulon product with the supplied diluent and use immediately; other products have different storage limits.