Yesterday Brian Hosie, of the Scottish Agricultural College Veterinary Services, warned sheep farmers to keep their livestock away from these toxic shrubs.
"Sheep will usually avoid rhododendron bushes if other sources of food are available but in winter it is not unusual for sheep to break into ornamental gardens and woodland and nibble on green leaves as the heavy snow bends rhododendron branches within reach."
He confirmed that the SAC Disease Surveillance Centres had already dealt with several cases of poisoning since the snow began. "In most cases little can be done to treat the sheep," Hosie said.
"Rhododendrons contain a poison which, among other things, slows the heart and lowers blood pressure. The symptoms sheep show include drooling, vomiting, pain and distress. They stagger and collapse before dying."
Other plants such as azaleas, a relative of rhododendrons, and pieris are also toxic, as is the yew tree, which can be problematic in severe winters.
Sheep are not alone in suffering from rhododendron poisoning as the toxins can also affect cattle and even humans. Hosie pointed out that one of the earliest human cases recorded involved Greek soldiers who, around 400BC, were reputedly killed by rhododendron honey.
Hosie recommended that shepherds and hobby farmers who keep sheep inspect their field boundaries and move sheep from fields where there is a danger they will eat rhododendrons or any other poisonous plants.
l NFU Scotland has welcomed the "crucial concession" in extending driver working hours with a spokesman saying the number of transport-related problems was growing rather than easing.
Milk collection from some farms had been disrupted and some producers had to pour out milk because there was no collection service. Animal feed deliveries were "problematic" and fuel supplies erratic. One Aberdeenshire farmer visited five filling stations before finding one with diesel.
The extension of the permitted driving hours up to ten hours runs to midnight on Saturday.