What is the long-term effect of neutering age on weight and body condition score in cats?

7 July 2025

Although it’s well established that neutered cats are more predisposed to obesity, there has been limited research on whether age at neutering influences body condition score (BCS) and bodyweight through different life stages. Lack of long-term clinical research on the risks and benefits of prepubertal neutering has been highlighted as a barrier to neutering uptake by some veterinary surgeons.

A new study, conducted as part of the Bristol Cats Study and published in Vet Record, has explored associations between age at neutering and age-related increases in bodyweight and BCS in cats¹.

Using longitudinal clinical records of BCS and bodyweight, paired with age at neutering and other owner-reported auxiliary information, the researchers assessed factors that influence BCS and bodyweight as cats age.

The final dataset included 584 individual cats, with BCS recorded at 2410 veterinary visits, and bodyweight at 2073 visits. Of these, 21% were neutered at 4 months or under, 36% at 5 months, 33% at 6 months, and 9% between 7 and 12 months. A BCS of 3 (ideal) was recorded at 67% of veterinary visits, while a BCS of 4 (overweight) was recorded at 26%, a BCS of 5 (obese) at 9%, and 2 (underweight) at 4%. The mean bodyweight recorded across all visits was 4.73 kg.

Consistent with other studies, age was a significant predictor of BCS and bodyweight, with both increasing in earlier life until 9 years of age, and then beginning to decrease.

Cats neutered prepubertally showed no difference in bodyweight or BCS, compared to cats neutered at 5 or 6 months, with all three age groups having similar bodyweight trajectories throughout their lifetime. There were differences between cats neutered at 6 months old or younger and those neutered between 7 and 12 months old. Cats neutered between 7 and 12 months didn’t experience such a rapid rate of increase in bodyweight and BCS as those neutered at 6 months or under.

It’s not yet clear why cats neutered at an older age may show size differences post-neutering, compared to cats neutered before 7 months old, although it’s possible that neutering later may be protective against excess weight gain later in life.

Sex was an important factor, with female cats having a lower bodyweight and BCS than males. This was associated with season, with bodyweight and BCS differences more pronounced in the summer and autumn, which may be due to variation in food intake throughout the year.

Hair length was predictive of BCS only, potentially due to the subjective nature of BCS measurements, with longhaired cats having a lower BCS than shorthaired cats.

These findings contribute to the increasing evidence indicating that cats neutered prepubertally are not at higher risk of becoming obese compared to those neutered at around six months old. Therefore, when considering weight management, proactive dietary management and other lifestyle approaches should be encouraged for all cats neutered at 6 months old or younger.

Limitations of the study include possible inaccuracies of owner-reported date of birth for their cat, and therefore the calculated age at neutering and at each BCS and bodyweight measurement, and use of the five-point BCS scale rather than the nine-point scale, which may result in vets routinely rounding down in scores. It also wasn’t possible to assess welfare impacts or incorporate diet and lifestyle measurements into the study.

Take home message

Cats neutered prepubertally do not experience increased weight gain and are at no greater risk of developing obesity, compared to cats neutered at the historically recommended 6 months. Cats neutered between 7 and 12 months had the lowest risk of future increases in BCS and bodyweight. Post-neutering weight management advice is recommended for all cats, and monitoring should include both BCS and bodyweight, particularly for longhaired cats.

Reference

¹Foreman-Worsley R et al. (2025) Long-term effect of neutering age on body condition score and bodyweight in domestic cats. Vet Record. https://doi.org/10.1002/vetr.5433