Plot: In this, the 900th edition, John Craven pays a lighthearted tribute to the unsung heroes and heroines of the British countryside - its animals. Ben Fogle reports on how pigs are the unlikely saviours of the ponies of the New Forest, Michaela Strachan meets the Newfoundland dogs which save lives at the sea, while Charlotte Smith finds out what is being done to safeguard the future of water vole