Understanding split sexing and why the standards require it

From 3 March 2026, pigs must be ‘split-sexed’, i.e. male and female pigs should be moved into separate pens, by the time they reach an average weight* of 50kg. This has been reduced from 110kg in the 2016 version of the standards.

This is an important change because females in mixed-sex groups are frequently subjected to aggression and mounting by males - and a large number of pregnant gilts are being slaughtered in abattoirs. Continuous mounting by males causes various welfare issues:

• Stress: they can’t escape. Males will also constantly nudge the female, prior to mounting.
• Pain: as males are heavier, mounting causes damage to the females’ joints, particularly cartilage.
• Injuries: in severe cases, sows can suffer fractured limbs or back. Males can also be injured when mounting females.

An EFSA (European Food Safety Authority) report said:

“The proportion of gilts pregnant at slaughter in the UK is significant. Reports from vets working in abattoirs indicated pregnancy prevalence of at least 10% and up to 40% in extreme cases. These gilts are likely to be in early pregnancy in most cases because age at puberty will typically be 170–180 days and with current UK slaughter weights most gilts will be 160–180 days at slaughter. If entire males are kept in countries where slaughter weight and age is higher, this prevalence could increase, but would be easily avoided by split‐sex rearing.”

Although there is no conclusive evidence on whether foetuses feel pain, split-sexing of pigs will mean fewer pregnant gilts will be slaughtered, reducing the potential for suffering.

There are no legal protections for livestock foetuses at slaughter and legislation on stunning doesn’t make any special provisions for pregnant animals.

Split-sexing also allows producers to tailor their pigs’ diet. Male and female pigs need slightly different diets to grow efficiently - and by tailoring diets, muscle growth can be improved.

Will it cost producers lots of time and money to change their systems and the way they work?

We know that approximately half of RSPCA Assured members already practise split-sexing.

We acknowledge other members may need to change the set-up of their facilities and ways of working in order to achieve this standard. For this reason, the standard doesn’t come into force until 2026 to allow producers time to plan and adjust.

Producers rarely have an equal number of male and female pigs - won’t this make splitting them up difficult?

The number of male and female pigs is rarely equal, and on most farms, the pens pigs are kept in are a set size - so there may be too many of each sex to fit in the available pens and still meet the standards in relation to space requirements.

The RSPCA wants to avoid producers running out of pens or having to house pigs on their own. For this reason, the standards allow up to 5% of the herd to be kept in mixed sex pens to help with pen allocation management. So on a unit with 200 pigs, up to 10 pigs could be kept in a mixed-sex pen.

Any ‘smalls’ can also be put into mixed sex pens, but these mixed groups of smalls mustn’t make up more than 10% of the herd. ‘Smalls’ are smaller pigs that are less robust and need separating from other pigs in the main herd to avoid unfair competition from stronger pigs. Farms don’t usually have many extra pens for smalls, so it might be difficult to split-sex them.

If more than 10% of a herd is made up of smalls, the RSPCA considers this to be a high number. It indicates there may be a reason why increased numbers of smaller, weaker pigs are being born - and this needs to be addressed.

The hospital pen (a warm, comfortable area where sick pigs receive treatment and recover) can also contain both sexes at the same time - also because most farms don’t have many hospital pens, so split-sexing could be difficult to achieve.

It’s a big step forward for pig welfare for a minimum of 85% of pigs on RSPCA Assured farms to be split-sexed - and whilst in an ideal world it would be 100%, the RSPCA has made these allowances in the hope it will make the new standard more practical and achievable for RSPCA Assured members.

If you need any support in meeting this standard, or have any questions, please reach out to our farming engagement team.

If you want to find out more about split sexing, we’ve listed some great research resources for you below:

1. Rydhmer, L., Zamaratskaia, G., Andersson, H. K., Algers, B., Guillemet R., & Lundström, K. (2006). Aggressive and sexual behaviour of growing and finishing pigs reared in groups, without castration. Acta Agriculturae Scandinavica, Section A — Animal Science, 56(2), 109-119.
2. Kritas, S. K., & Morrison, R. B. (2004). An observational study on tail biting in commercial grower-finisher barns. J Swine Health Prod. 12(1):17-22.
3. Vanheukelom, V., Van Beirendonck, S., Van Thielen, J., & Driessen, B. (2012). Behavior, production results and meat quality of intact boars and gilts housed in unmixed groups: A comparative study. Applied Animal Behaviour Science, 142(3–4), 154-159. https://doi.org/10.1016/j.applanim.2012.10.004.
4. Hartnett, P.; Boyle, L.; Younge, B.; O’Driscoll, K. The Effect of Group Composition and Mineral Supplementation during Rearing on Measures of Cartilage Condition and Bone Mineral Density in Replacement Gilts. Animals 2019, 9, 637. https://doi.org/10.3390/ani9090637
5. Hartnett, P., Boyle, L. A., & O’Driscoll, K. The effect of group composition and mineral supplementation during rearing on the behavior and welfare of replacement gilts. Translational Animal Science, Volume 4, Issue 2, April 2020, Pages 1038–1050. https://doi.org/10.1093/tas/txaa002
6. Björklund, L., & Boyle, L. A. (2006). “Effects of Finishing Boars in Mixed and Single Sex Groups and Split Marketing on Pig Welfare.” Acta Veterinaria Scandinavica 48 (1):P2.