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Other lamb castration methods
Information about lamb castration methods that are not common in England.
As well as common lamb castration methods there are a couple of new methods that can be used in England:
- Castration with a crush clip (e.g ClipFitter)
- Castration with use of anaesthetic simultaneously (e.g Numnuts®)
The following methods are not currently approved for use in England:
- Immunocastration
- Chemical/hormonal castration
There is less evidence about the impact of these practices on animal welfare, productivity, profitability and/or environmental sustainability, compared with the more common methods.
Castration clip (ClipFitter)
This technique combines aspects of both rubber ring castration and the clamp technique.
It uses a clip that is clamped around the scrotum. The clip must be applied using a specialised tool, similar to a set of pliers.
The clip crushes the nerve and spermatic cords almost instantly, and the blood supply is subsequently cut off.
The ClipFitter method is authorised by the Scottish government for use in lambs up to three months of age without anaesthetic, as it is seen to be equivalent to burdizzo clamping.
The law is different In England and Wales, where the ClipFitter method can be used in lambs up to 7 days of age, as it is seen by Defra and the Welsh Government to be equivalent to rubber ring castration.
You apply the clip in a similar position to a rubber ring/clamp, and it remains on the animal until it is shed with the wasted scrotum from around three weeks after application.
In this way, it is similar to combined castration with rubber ring and Burdizzo clamping, but in one step.
A range of applicators and clips are available to accommodate lambs of different sizes (5–20 kg). It is very important that the appropriate size of clip is used for each lamb.
Care must be taken to ensure that clips are applied across the scrotum rather than pointing ‘head to tail’ to prevent trapping the penis in the clip.
The ClipFitter method was trialled by Scotland’s Rural College (SRUC) in 2022 and the results of this study indicate that young lambs (less than seven days old) castrated with ClipFitter expressed similar behaviour to uncastrated handled lambs, and showed a significantly lower pain response compared to rubber ring castration.
In older lambs (4–5 weeks old), ClipFitter caused an increased pain response shortly after application compared with the clamp method plus pain relief.
However, after 18 minutes, there was no significant difference seen between lambs which were castrated with ClipFitter, the clamp method plus pain relief, and uncastrated handled lambs.
Castration with anaesthetic (Numnuts®)
Numnuts® aims to blocks the acute pain that follows castration of lambs with rubber rings. It consists of a rubber ring applicator, combined with an injector that dispenses local anaesthetic.
This method was developed in Australia and has been in use there since 2019. It was launched in New Zealand in 2021. Numnuts® was launched in the UK in 2024.
The method is approved for use in Scotland for lambs up to three months of age due to the addition of local anaesthetic.
However in England (and Wales) it is only approved for lambs up to seven days of age due to the Mutilations (Permitted Procedures) (England) Regulations (2007) which currently prohibit the use of rubber rings, with or without anaesthetic, on animals older than seven days.
The method was trialled by Scotland’s Rural College (SRUC) in a Defra-funded study in 2022. This study assessed the use of Numnuts® for castration and/or tail docking in lambs under seven days of age
The results suggest that the Numnuts® technique was effective at eliminating the pain response associated with tail docking.
However, there was no reduction in pain-related behaviours seen in lambs castrated with Numnuts® (using a 1 ml dose of procaine local anaesthetic) compared with rubber ring castration.
In Scotland, Numnuts® can be used to castrate lambs up to 3 months of age.
Studies from Australia report that in lambs aged between 4 and 10 weeks, Numnuts® appeared to be an effective way to deliver lidocaine (a local anaesthetic) and improve the welfare outcomes during the acute pain phase (5 and 20 minutes post application) but did not eliminate pain behaviours completely.
Further research found the effects of the local anaesthetic procaine to last longer than lidocaine, and bupivacaine was slower to take effect but appeared to provide longer-lasting relief.
This study also noted that, in general, the effect of local anaesthetics in sheep is relatively short. Currently (June 2025), procaine is the only local anaesthetic which is licensed for use in sheep in the UK.
Immunocastration
Immunocastration is a non-surgical, painless method of castration that uses a protein injection (vaccine) to reduce reproductive hormones in animals.
Two injections are needed:
- Primary dose
- Booster
Rams need gonadotrophin-releasing hormone (GnRH) to reach sexual maturity.
The vaccine prevents GnRH from being released, making ram lambs infertile.
Castration via this method is reversible and the duration of infertility will depend on the interval between the primary and booster vaccination.
In the UK, immunocastration is licensed for pigs and has also been used on cattle; it cannot, however, be used on sheep.
International trials have highlighted the potential for immunocastration to improve the welfare, performance and meat quality of ram lambs.
Immunocastration provides similar fertility control and behavioural management to other castration methods but with productivity levels more akin to entire males.
In countries where immunocastration is permitted, the vaccine can be safely used on lambs from six weeks of age.
There is a risk that should the procedure fail, alternative castration methods may be limited due to the age of the animal.
Potential advantages over traditional castration methods:
- Easier management
- Less labour
- Improved welfare, e.g. reduced injuries
- Flexibility in timing
The flexibility would lend itself to being used across a range of systems, including those that do not routinely handle young lambs.
It could also enable you to make the most of the improved growth rates of entire lambs until reaching sexual maturity.
Chemical castration
Chemical castration involves injecting chemicals into the testes to reduce testosterone production.
Examples of the chemicals used on other species include lactic acid, zinc gluconate and zeranol implants.
These cause inflammation and destroy testicular function, resulting in infertility.
Serious side effects have been reported, including muscle wastage, anaemia and osteoporosis.
The lack of research and evidence for the use of chemical castration in sheep, and the reported side effects seen in other species, makes this method unlikely to be approved as a viable alternative to existing and/or emerging techniques.