National Sheep Association chief executive Phil Stocker said ‘the decimation of breeding flocks on some farms is going to be a real problem’.
Mr Stocker added: “Individual businesses will have difficult decisions to make about whether they buy-in replacement stock.
“Even if cash flow allows such an option, for some farmers, such as those running hefted flocks in upland areas, it will not be possible to replace like-for-like.
“I worry many poorer breeding ewes which would normally have been culled will be kept for next breeding season. This will impact efficiency and profitability well into the future.”
Gareth Wyn Jones, who farms in the Conwy Valley, Wales, said it was now a case of ‘salvaging what is left’.
He said: “Just in our small farming community here we have had hundreds of sheep deaths.”
Farmer Frank Jackson, who lost dozens of sheep in snow drifts up to six metres (20ft) near Marton, Cumbria, said many of the ewes were pregnant.
He said: “This is the first time ever we have lost this amount of sheep. It has been the worst weather for the end of March for at least 15 years.”
Stuart Mactier said one of his sheep had a lucky escape when it was trapped in drifts for 11 days.
Mr Mactier, who runs 1,800 ewes at Newton Stewart, Dumfries and Galloway, said he was ‘flabbergasted’ when he and his brother found the in-lamb sheep alive.
Farm chiefs said the lack of grass was a major concern and fear the financial burden of buying-in additional feed will be ‘overwhelming’ for some businesses.
The Met Office said there is a good chance temperatures could begin to return towards seasonal average next week.
NFU fodder banks are now open. For NFUS fodder bank, call 0131 472 4059. In England and Wales, contact your local NFU.