Farming leaders said sheep farmers were facing a "war of attrition" from the weather after a severe winter followed a wet summer and autumn.
And they warned that it could affect productivity for the rest of the year.
Gary Mitchell, vice-president of NFU Scotland, said spring lambs were having a "really tough time".
He told BBC Radio Scotland's Newsdrive programme: "One woman contacted me to say one afternoon she'd lost 17 lambs due to the cold weather. It's really severe."
Farmers in most parts of Scotland are forbidden from burying their fallen stock and must instead pay approved companies to collect the carcasses.
The collectors are reportedly experiencing high levels of demand.
One farmer in Aberdeenshire told BBC Scotland said he had been waiting three days for a dead sheep to be collected.
Poor harvest
The National Fallen Stock Company said the turnover of dead sheep and lambs stood at £373,000 in March - up by almost 40% on the same period last year.
John Fyall, of the National Sheep Association, said the wet weather last year made cutting silage and hay difficult and it led to a poor harvest.
The prolonged cold spell this spring means the grass is not growing for the animals to eat.
He said that was leading to nutritional problems in lambs - some are not getting enough disease-fighting colostrum from their mothers.
Although they were surviving the first couple of weeks of life, Mr Fyall said large numbers were dying at two to three weeks old.
"It's harder to take the losses when they're a few weeks old as you think the hard work is done by then," he said.
He said farmers were enduring a "war of attrition" from the prolonged period of difficult weather.
They are spending more on feeding their livestock, and many are having to shell out further to have their dead animals taken away.
More machinery is suffering wear-and-tear, breaking and getting stuck in muddy conditions.
'Significant watershed'
And some farmers are feeling demoralised, working in energy-sapping wet conditions for little financial reward.
Mr Fyall said the price of lamb was good at the moment, but the farmers who were putting in the hard work now received a poor price for their stock last autumn.
He warned that unless farmers were paid fair prices, some would leave the industry altogether.
He said: "We've got to have a good price for our product. If we don't, we could see a significant watershed in the industry.
"People are really getting fed up. They know they will get paid more for planting trees."
And he added that the poor start to spring was likely to have a knock-on effect for the rest of the year.
"An awful lot of land has not even been ploughed yet," he said. "If there's less growing time, there's lower yields."
A Scottish government spokesman said:"We appreciate the challenges that Scottish farmers have faced due to the recent weather conditions and are working with relevant partners to support them.
He added: "We will continue to engage with the farming community and local authorities, and are always open to dialogue."
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