# Gonadorelin (GnRH): veterinary dose and monograph

> Gonadorelin (GnRH) is a veterinary drug. Synthetic gonadotrophin-releasing hormone (GnRH) — a reproductive hormone that stimulates the pituitary to release LH (and FSH), triggering ovulation and supporting luteal function. Indications include 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). This monograph lists 6 reference doses for dogs, cats, cattle, goats and ferrets, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/gonadorelin · Last reviewed: 2026-10-01

## 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

*Gonadorelin (GnRH) doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| GnRH-stimulation test (castrated vs cryptorchid) | 50 µg per dog IM (or 2.5 µg/kg IM; 25 µg for very small dogs), testosterone before and 60–180 min after | IM | single dose | — |
| Reproductive therapy (cryptorchidism, libido, ovarian cysts) | 50–100 µg per dog IM/SC q24–48h, or ovarian cysts 3.3 µg/kg IM daily for 3 days | IM | per indication | — |

- 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

*Gonadorelin (GnRH) doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Ovulation induction / ovarian-remnant test | 25 µg per cat IM once | IM | single dose | — |

- 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

*Gonadorelin (GnRH) doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Cystic ovaries / Ovsynch / conception | 100 µg per cow IM or IV (lactating dairy cows 100–200 µg IM) | IM | once, or per synchronisation protocol | — | no slaughter withdrawal |

- 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

*Gonadorelin (GnRH) doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| No reference dose for this species | Not established in Papich 5e or Plumb’s 10e — do not extrapolate from another species | — | — | — |

- 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

*Gonadorelin (GnRH) doses for goats*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Out-of-season ovulation induction (does) | 100 µg per doe daily for 4–5 days | IM | q24h × 4–5 days | — | Withdrawal NOT established — treat as extra-label |

- 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.

*Gonadorelin (GnRH) doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Cystic ovaries / Ovsynch / conception | 100 µg per cow IM or IV (lactating dairy cows 100–200 µg IM) | IM | once, or per synchronisation protocol | — | no slaughter withdrawal |

- 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

*Gonadorelin (GnRH) doses for ferrets*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Terminate oestrus (induce ovulation) | 20 µg per ferret IM; repeat in 1 week if needed | IM | once, repeat in 7 days | — |

- 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

> **Caution:** 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.

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## Frequently asked questions

### What is the dose of Gonadorelin (GnRH) for dogs?

Reference doses for Gonadorelin (GnRH) in dogs: 50 µg per dog IM (or 2.5 µg/kg IM; 25 µg for very small dogs), testosterone before and 60–180 min after IM single dose (GnRH-stimulation test (castrated vs cryptorchid)); 50–100 µg per dog IM/SC q24–48h, or ovarian cysts 3.3 µg/kg IM daily for 3 days IM per indication (Reproductive therapy (cryptorchidism, libido, ovarian cysts)). Confirm against the label and the patient before use.

### What is the dose of Gonadorelin (GnRH) for cats?

Reference doses for Gonadorelin (GnRH) in cats: 25 µg per cat IM once IM single dose (Ovulation induction / ovarian-remnant test). Confirm against the label and the patient before use.

### What is the dose of Gonadorelin (GnRH) for cattle?

Reference doses for Gonadorelin (GnRH) in cattle: 100 µg per cow IM or IV (lactating dairy cows 100–200 µg IM) IM once, or per synchronisation protocol (Cystic ovaries / Ovsynch / conception). Confirm against the label and the patient before use.

### What is the withdrawal period for Gonadorelin (GnRH)?

Cattle, IM (Cystic ovaries / Ovsynch / conception): no slaughter withdrawal; Goats, IM (Out-of-season ovulation induction (does)): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Gonadorelin (GnRH) not be used?

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.

### What are the side effects of Gonadorelin (GnRH) in animals?

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

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.