Common causes
Soft stools are common around weaning and after the move to a new home, when stress and new food come at the same time. Other common causes are overeating, roundworms and the parasites coccidia, giardia and tritrichomonas, as well as bacterial and viral infections. Panleukopenia and feline coronavirus can also start with diarrhoea. In a cattery several causes often occur together, which is why a single test rarely gives the whole answer and why a kitten that seems to recover can relapse when it is stressed.
When it is urgent
Contact a vet the same day if a kitten has bloody or watery diarrhoea, vomits, stops eating, seems lethargic or feels cold, or if several kittens fall ill at once. Small kittens can become dehydrated within hours. Weigh the kittens every day: a kitten that stops gaining or loses weight needs attention even if the stool only looks a little soft. You can check hydration by gently lifting the skin over the shoulders. It should spring back straight away, and dry, sticky gums are a warning sign.
Testing and treatment
Bring fresh stool samples, ideally collected over three days, since many parasites are shed on and off. The vet can test for worms, coccidia and giardia and run a PCR panel that also covers tritrichomonas and viruses. Treatment depends on the cause: for example fenbendazole for giardia and worms, toltrazuril or ponazuril for coccidia, and ronidazole for tritrichomonas, which is only used under close veterinary supervision. Avoid antibiotics without a diagnosis, since they rarely help and can make things worse. Probiotics and a bland, easily digested diet support recovery.
Hygiene and prevention
Giardia cysts and coccidia survive for a long time and reinfect kittens from litter and paws. Scoop litter boxes at least twice a day, clean and dry them thoroughly, and wash bedding often. Bathing the hindquarters at the end of a giardia treatment removes cysts from the coat. Change food gradually over a week, and give the new family a bag of the food the kitten is used to. Deworm according to your vet's plan, test new cats before they join the cattery, and note stool quality and weight in the litter log so you spot changes early.