Farmers in the Peak District, Cumbria, Yorkshire and parts of Scotland struggled to get to their stock at a time when many are still lambing.
Heavy drifting snow over the weekend has placed many ewes and lambs in peril and severely disrupted the delivery of vital feed and fuel stocks.
In Dumfries and Galloway and parts of Argyll and the Islands, the daily collection of milk has also been badly affected with several farmers having to pour away overflowing tanks.
Many roads are still impassable, with the Met Office issuing severe weather warnings for snow and ice.
Thousands of homes in Scotland and Northern Ireland have been left without power since the weekend, after snow and strong winds damaged cables.
NFU Scotland Dumfries and Galloway regional chairman Andrew McCornick, who farms at Barnbackle, Lochfoot, Dumfries, said: “We are well through our annual lambing so the snow couldn’t have hit at a worse time.
“We have managed to dig our way around most of the fields with ewes and lambs in them. We managed to get feed to those that we have found and we have been digging many of them out of the snow.
“The drifting snow is so bad that there are still many vulnerable sheep that we are still battling to get to and we know that we are likely to face losses when the snow has cleared.”
NFU Vice President Adam Quinney said: “These are unusual conditions and are totally out of character for the time of year. Farmers are resilient and are working around the clock to look after the welfare of their animals.
“It has put an extraordinary strain on the industry after what has been a torrid 12 months of extreme weather, compounded by the fact that many farmers’ sheep are lambing at the moment.
“You will find farmers up and down the country helping to ensure roads are clear so feed deliveries can make it onto farm, and in many cases bringing animals inside to protect against the elements.”