Scientists in Sweden have found evidence that the breeding of pedigree dogs for appearance has led to a dramatic decline in the animals? intelligence.

The author of the report, Kenth Svartberg, from Stockholm University, tested 13,000 dogs across 31 different breeds on various characteristics.

He said: ?Modern breeding practices are affecting the behaviour and mental abilities of pedigree breeds as well as their physical features.?

The worst affected working breeds are smooth collies and Rhodesian ridgebacks.