Researchers at the University of Guelph evaluated the mean body weight over the lifespan of more than 19 million cats. They reviewed the medical records from veterinary clinics in the United States and Canada from 1981 to 2016. The results of the study showed that 52% of cats only had one body weight noted in the records. The mean body weight of the 4 most common recognized breeds (Siamese, Persian, Himalayan, and Maine Coon Cat) peaked between 6 and 10 years of age and then declined. Mean body weight of short, medium, long haired domestic cats peaked at 8 years. These cats weights were significantly higher when they were neutered as compared to sexually intact cats. Not surprisingly, the mean body weight of neutered 8-year-old domestic short, medium, or long haired cats increased between 1995 and 2005 but was steady between 2005 and 2015.

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Investigation of relationships between body weight and age among domestic cats stratified by breed and sex