The disinfected hay and Keep Out notices at the entrance to Balsdean Farm are a stark reminder of the foot-and-mouth crisis.

There is an eerie silence surrounding the remote farmhouse. Normally, cars have to slow down for at least one horse-rider on the long road up to the farm, which leads to the bridle paths over the Downs towards Lewes.

But there are no riders, as responsible owners are heeding the warnings not to ride on the Downs for fear of spreading the highly contagious disease.

With the latest count of the outbreak in Britain reaching 168, it seems the majority of cases have been spread by movements through Longtown Market in Cumbria and by a dealer in Devon.

It is by luck, rather than judgement, that movements of sheep and cattle to and from Sussex have not involved these areas.

John Carr said the current outbreak was worse than the one in 1967.

He said: "We could take lambs to the abattoirs then but now nothing is moving.

"The reason we have no foot-and-mouth in Sussex is because none of the sheep movements have involved the Longtown Market or Devon. It is just lucky no Sussex sheep farmers have been dealing with these areas."

There is also a school of thought that believes foot-and-mouth does not spread so easily on chalk soil.

John and Martin are among the biggest sheep farmers in the South of England and they cannot move the 10,000 sheep they have on grassland across the south and east of the country.

Most of their flock is grazing on environmentally-sensitive areas of the South Downs and the Carrs and their staff are on a constant lookout for foot-and-mouth.

Martin said: "It's difficult to spot in sheep. Normally, the first sign is a sheep hanging behind the rest of the flock but there are also many other reasons why it might do that.

"If in doubt, you have to check the hooves for small blisters but often these are difficult to spot as well.

"It's not much fun being a sheep farmer at the moment."

As soon as the first case of foot-and-mouth was announced in Britain, the Carrs took immediate action and brought 1,700 breeding ewes they had in the South back to land near their farm.

This was before the Ministry of Agriculture announced any restrictions on the movement of livestock.

John said: "We knew there would be restrictions so we had to get them back as quickly as possible, particularly before the lambing season started."

With so many lambs in a restricted place, it creates another problem at this time of year. There is not enough grass so they have to be fed special fodder, which increases the cost.

Already, the price of lambs going to the slaughterhouses has decreased. Before the outbreak it was £48 now it is £38 and could fall further.

John warns, if the crisis continues and feeding costs escalate, there could come a time when the cost of feeding each lamb would outweigh the price at which it could be sold.

John said: "It is horrendous. We are shelling out hundreds for feeding and getting nothing back. At the moment, we have no cash flow.

"Then there is the problem of imported lamb that is coming into the country via the supermarkets.

"At the same time, the price of meat in the shops is increasing and people think it's going to the farmers but it's not."

The Carrs also have 2,500 sheep stranded in Suffolk, which they were hoping to bring back to Sussex but a lorry on that farm was found to have visited another farm where there had been a foot-and-mouth case.

John said: "The Ministry of Agriculture said this was a very small risk but we don't know how long they will be there."

The restrictions on movement are costing the Carrs thousands of pounds a week.

When sheep cut their first two teeth they lose about half their value.

With hundreds of sheep coming to the age when their first main teeth come through, the value of the flocks across the South is going down daily.

The lambing season is also approaching and this too will present problems.

Normally, lambing is done in a huge barn at Piddinghoe, between Lewes and Newhaven but restrictions mean they will only be able to lamb a small proportion of their flock there.

More lambing will have to take place in the open fields, which will see the weakest of the newborn die.

It will also be more labour intensive and already, they are having to employ more staff.

Martin, 25, said he was angry the Plumpton race meeting went ahead yesterday. He said: "We are doing everything we can to prevent the spread of foot-and-mouth and have told all horse owners on our land not to move away from the farm.

"Yet we find horses being brought to Sussex from all over the country.

"It seems there is one rule for horse racing and another for the horse owners of this country.

"We are just hoping everything will get back to normal soon but that will only happen with the public's help and understanding."