- Post-mortem examinations were performed on 29 deceased Persian kittens from 13 different litters, and 30 deceased Devon Rex kittens from 18 different litters in order to identify gross anatomical abnormalities. Fifteen kittens were stillborn (8 Devon Rex, 7 Persian), 17 kittens died during the first day of life (16 Devon Rex, 1 Persian), 14 kittens died later in the first week of life (5 Devon Rex, 9 Persian), and 13 kittens died during the second week of life (1 Devon Rex, 12 Persian). The average age at death excluding stillborn kittens was 5.2±4.7 days for both breeds, 1.8±2.0 days for Devon Rex kittens, and 8.5±4.2 days for Persian kittens. The most common sign reported by the cat breeders before death was dyspnea, with 12 kittens affected (11 Devon Rex, 1 Persian). Postmortem examination findings included pyothorax (9 Devon Rex kittens), pigmenturia (4 Devon Rex, 2 Persian kittens). It is estimated that at least 22.0% (13/59) of neonatal mortalities were due to infectious etiologies, at least 6.8% (4/59) were due to noninfectious etiologies, (n=7), and up to 71.2% (42/59) were classified as idiopathic.