Evidence for seasonal reproduction in UK domestic cats.

Objectives: The aims of this study were to analyse a large body of data obtained by the Royal Society for the Prevention of Cruelty to Animals (RSPCA) Greater Manchester Animal Hospital on the breeding pattern of owned domestic cats in the UK, and to provide clear statistical evidence of whether seasonal variation remains present in temperate climates.

Methods: The total number of cats spayed and the number of cats found to be pregnant were recorded on a monthly basis from December 2005 to July 2014 by the RSPCA Greater Manchester Animal Hospital. The percentage of cats found to be pregnant was calculated for each month and the 8.5 years of data were binned into calendar months. The mean and SD of the monthly pregnancy rate was calculated for each calendar month bin, as was the difference between the mean percentage of detected pregnancies and the global mean. The Z score for each month's difference was then calculated.

Results: Data were available for 5414 cats neutered during the 8.5 consecutive years of this study. A global average of 8.9% of cats spayed were found to be pregnant. The mean calendar month pregnancy rate exhibited a very significant variation, with the highest positive deviation being in April (Z score +2.9) and the highest negative deviation being in November/December (Z score -4.5). When aggregated into 3 month averages, an extremely significant difference between 'spring' and 'winter' months of >7 SE (P <<0.01) was found.

Conclusions And Relevance: This study provides clear statistical evidence, from a large data set, that seasonal breeding patterns are still present under UK temperate conditions. We discuss the impact that this has on charity rescue shelters and propose that a campaign targeted at clients of animal welfare charities encouraging autumn neutering will be the most cost-effective method of cat population control, and help relieve the demand on welfare charity resources.