Gonadorelin (GnRH): veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

GnRH, Cystorelin, Factrel, Fertagyl

Species with doses

Dogs, Cats, Cattle, Goats and Ferrets

Routes

IM

Last reviewed

1 October 2026

Indications

• Bovine cystic ovarian disease (follicular cysts) — luteinisation/ovulation
• Ovulation synchronisation programmes (Ovsynch/timed AI) in cattle
• Improving conception rates when given at/after breeding (cattle)
• Ovulation induction and diagnostic GnRH-stimulation testing (mares/small animals)

Gonadorelin (GnRH) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• GnRH-stimulation test (castrated vs cryptorchid): Plumb’s p.592: 50 µg IM with a sample 2–3 h later (Pinto); 2.5 µg/kg IM with a sample at 60–90 min (Freshman). Castrated dogs stay below 0.1 ng/mL testosterone.
• Reproductive therapy (cryptorchidism, libido, ovarian cysts): Papich 5e: 50–100 µg/dog/day q24–48h IM. Plumb’s p.592: testicular descent 50–100 µg SC or IV, repeat in 4–6 days (Cox); libido 50–100 µg IM weekly for 4–6 weeks (anecdotal); cystic ovarian disease 3.3 µg/kg IM once daily for 3 days, confirm with progesterone >2 ng/mL 1–2 weeks later (Purswell).

Cats

• Ovulation induction / ovarian-remnant test: Papich 5e: 25 µg/cat once IM. Plumb’s p.592: after mating to induce ovulation (Morgan); ovarian remnant — progesterone >1 ng/mL 1–2 weeks later confirms ovarian tissue (Purswell). Male infertility/testicular descent 1 µg/kg every 2–3 days (Verstegen).

Cattle

• Cystic ovaries / Ovsynch / conception: Papich 5e: 100 µg per cow IM or IV once (about 2 mL of the diacetate tetrahydrate product); lactating dairy cows 100–200 µg IM. Plumb’s p.592 (Cystorelin, Factrel labels): ovarian cysts 100 µg IM or IV. Dosed per animal, not per kg.

Horses

• No reference dose for this species: Neither Papich 5e nor Plumb’s gives a gonadorelin dose for mares; deslorelin or hCG are the referenced ovulation inducers.

Goats

• Out-of-season ovulation induction (does): Plumb’s p.592 (Smith 1986). Follow local label/FARAD guidance for withdrawal.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Cystic ovaries / Ovsynch / conception: Papich 5e: 100 µg per cow IM or IV once (about 2 mL of the diacetate tetrahydrate product); lactating dairy cows 100–200 µg IM. Plumb’s p.592 (Cystorelin, Factrel labels): ovarian cysts 100 µg IM or IV. Dosed per animal, not per kg.

Ferrets

• Terminate oestrus (induce ovulation): Plumb’s p.592 (Williams 2000): most effective about 14 days after the onset of oestrus.

Contraindications

Known hypersensitivity. Pregnancy where disruption is undesirable (though GnRH is used within repro protocols). Use outside an appropriate reproductive protocol/timing (ineffective). Observe any food-animal considerations.

Adverse effects

• Very well tolerated — minimal side effects
• Transient behavioural change (LH/testosterone surge in males)
• Occasional local injection-site reaction

Drug interactions

• Prostaglandins (PGF2α/cloprostenol): sequential partners in synchronisation protocols (Ovsynch)
• Progesterone devices (CIDR): combined in timed-AI programmes
• No major adverse pharmacologic interactions

Pregnancy and lactation

Used within reproductive protocols; not for disrupting a wanted pregnancy. Generally safe as a single physiologic-hormone dose.

Monitoring

• Ovulation/luteal response (ultrasound/progesterone) and conception outcomes
• Cyst resolution (ovarian ultrasound/rectal palpation) in cystic ovarian disease
• Protocol timing (the key determinant of success)

Toxicity and overdose

Very wide safety margin — a single physiologic hormone dose is well tolerated with minimal adverse effects. No characteristic organ toxicity. The main "failure" is incorrect protocol/timing (no ovulatory response) rather than toxicity.

Management: Supportive only; no specific antidote needed (wide margin, short-acting hormone).

Clinical pearls

• The LH-surge trigger — a single GnRH dose ovulates a follicle or luteinises a follicular cyst, and it is the "GnRH" step of Ovsynch/timed-AI programmes in cattle
• Timing within the protocol is everything — GnRH → PGF2α → GnRH → timed AI (Ovsynch)
• A physiologic, well-tolerated hormone (dosed in micrograms per animal); also useful for GnRH-stimulation testing
• Remember the paradox: a single/pulsatile GnRH dose STIMULATES, whereas continuous GnRH-agonist exposure (deslorelin implant) SUPPRESSES the reproductive axis

Mechanism of action

Gonadorelin is identical to natural GnRH; a single dose acts on pituitary gonadotroph GnRH receptors to trigger a surge of luteinising hormone (LH) release (and some FSH). The LH surge induces ovulation of a mature follicle or luteinises a follicular ovarian cyst, and initiates/supports corpus-luteum formation — the basis of its use in ovulation synchronisation, cyst therapy and improving conception. (Continuous GnRH-agonist exposure, by contrast, down-regulates the axis — the principle behind deslorelin implants.)

Formulations and products

• Injection 50 mcg/mL (Cystorelin/Fertagyl)
• Injection 100 mcg/mL
• Cystorelin / Fertagyl / Factrel (Boehringer Ingelheim / MSD / Zoetis) — 50 / 100 mcg/mL, Injection

Storage

Injection: 15–30 °C (some refrigerated), protect from light; do not freeze.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other hormones, emergency drugs, supplements and other drugs

• Fluticasone (Inhaled)
• Fomepizole (4-MP)
• Glipizide
• Glycopyrrolate
• Heparin (Unfractionated)
• Hetastarch (Hydroxyethyl Starch)
• Human Chorionic Gonadotrophin (hCG)
• Hydrocortisone (Cortisol)

Frequently asked questions