Twinning Hormone for Sheep: What It Does, Risks and Alternatives

What farmers call the "twinning hormone" is not a single drug that makes a ewe carry twins. It is a hormonal programme designed by a veterinarian: heat synchronisation with vaginal sponges carrying a progesterone-like hormone (a progestagen), sometimes combined with a gonadotropin such as eCG (also called PMSG) that raises the number of eggs released. It can increase twins, but only in healthy ewes in good body condition, and only under vet prescription.

The question comes up again and again in farmer groups: "What is the injection for twins?" The honest answer is that an injection on its own does not create twins, and careless use can cost you ewes and lambs. This guide explains what actually happens inside the ewe, what a hormonal programme can and cannot do, the real risks, the natural alternatives, and how to judge the result with numbers rather than feelings.

What farmers mean by the "twinning hormone"

Litter size depends on how many eggs a ewe releases at ovulation. One egg gives one lamb; two eggs can give twins. The so-called twinning hormone usually combines two different tools:

• Heat synchronisation: a vaginal sponge with a progestagen stays in place for some days and is then removed, so most ewes in the batch come into heat within a day or two. This tool controls timing; by itself it does not raise the number of eggs. The general steps are covered in our guide to sponge oestrus synchronisation.
• Gonadotropins (such as eCG / PMSG): the vet may decide to give one at sponge removal. Its role is to stimulate the ovaries to release more eggs, and this is where the "twins" effect comes from.

The whole programme is therefore a veterinary prescription. The product, amount and timing are decided by the vet according to breed, age, season and flock condition. Rules for these products differ from country to country, and in most places they are available only on prescription.

What a hormonal programme can and cannot do

Response also varies a lot. Some ewes still release a single egg, others release more than is good for them, and the outcome for a batch cannot be predicted precisely.

The real risks nobody puts in the advert

• More lambs than the ewe can raise: triplets and quadruplets happen, and most ewes rear two well at most. Extra lambs need bottle feeding or fostering, or losses rise.
• Small, weak lambs: the bigger the litter, the lighter each lamb at birth, and the weaker its defence against cold, hunger and first-week disease.
• Ewe exhaustion: multiple pregnancies raise the risk of pregnancy toxaemia late in gestation, difficult births, and a sharp drop in body condition after lambing.
• Cost: hormones, sponges, vet visits, more rams because ewes come into heat together, more feed for the ewes and milk replacer for extra lambs.
• Unlawful or unsafe supply: products bought without prescription or from unknown sources may be fake or unsuitable, can break local rules and can harm the animal. Any waiting period before slaughter or milk sale is set by the vet only.
• Repeated use without review: running the programme every season on the same ewes without evaluation may reduce response over time; the decision belongs to the vet.

Why it fails without body condition and good feeding

The hormone sends the signal, but the ovary needs energy to answer. Thin ewes respond poorly; very fat ewes gain nothing and may become less fertile. Many vets want ewes at a medium body condition score, about 2.5 to 3.5 on a 1 to 5 scale, before any programme.

What happens before the programme matters more than the programme itself:

1. Flushing: raising energy gradually for a few weeks before mating already increases ovulation in medium-condition ewes. See flushing ewes before mating.
2. Ewe health: deal with worms, lameness and mastitis before the season, and vaccinate according to your local vet or ministry schedule.
3. Steady feeding after mating: a sudden feed cut in early pregnancy can lose embryos that were already there.
4. Heat stress: mating at the hottest time without shade and cool water lowers fertility in rams and ewes alike.
5. Rams: after synchronisation many ewes are in heat at once, so you need more sound rams, checked well before the season.

Natural ways to raise the twinning rate

Before thinking about hormones, these tools raise twins at lower cost and lower risk, and their effect builds season after season:

• Breed and prolific genetics: some breeds are known for large litters, others mostly give singles. Planned crossbreeding with a more prolific breed raises the ceiling itself.
• Ram choice: a ram born to a ewe that regularly has twins passes the trait to his daughters.
• Replacement policy: keep ewe lambs born as twins to dams with a repeated twin record, and cull ewes that have singles season after season.
• Ewe age: first-time lambers have more singles; twinning peaks in the middle productive years and drops with old age.
• Flushing and body condition: the cheapest tool you can use in the same season.

For a deeper look at these six factors, read how to increase the twinning rate in sheep.

How to measure the result with records

Whether you use a hormonal programme or only flushing, you will only know if it was the right decision by counting. For every ewe, record the mating date, the ram or artificial insemination, the scan result, the type of birth (single, twins, triplets) and the number of live lambs at weaning.

Then compare two batches: one that went through the programme and one that did not, or the same ewes in two seasons. Calculate:

• Lambs born per ewe lambed.
• Percentage of twins, and of triplets or more.
• Lambs weaned per ewe, because a twin that dies in its first week adds nothing.
• The extra cost of the programme against the extra lambs weaned.

In Throf, each stage sits on the ewe's record: natural or artificial insemination, pregnancy, birth including twins and triplets, miscarriage and weaning, and you can change the stage for a whole group at once. Insemination, pregnancy and births/twins reports show results per batch and per ram, while recorded expenses give you the cost per head. The question "should we repeat the programme?" then gets answered with your own flock's numbers.