A television advert that shows a guinea pig drinking Heinz tomato ketchup has been criticised by the RSPCA.
Guinea pigs should eat ketchup only as a rare treat, the RSPCA says
The commercial features a guinea pig in a cage drinking ketchup instead of water and finishes with the slogan "You can't eat without it".
The RSPCA says it sends out the wrong message to pet owners because water is an essential part of the animals' diet.
Heinz insisted the advert was a joke meant to imply that everything tastes better with its tomato ketchup.
The advert appears during commercial breaks for Emmerdale, as part of Heinz's sponsorship of the ITV1 soap.
A spokeswoman for the RSPCA said the charity was "bemused" by the advert.
She said: "Water is an essential part of a guinea pig's diet and we wouldn't recommend replacing it with ketchup.
"A small amount of ketchup as a treat now and again shouldn't do any harm as long as there is plenty of water available.
"We recommend feeding guinea pigs a diet of hay and grass and good quality cereal mix."
A Heinz spokesman said: "The advert is about exaggerating the fact that all foods taste better with Heinz Tomato Ketchup and in no way is Heinz encouraging families to copy the adverts."