(Severe) winter clearly has its influence on the energy 'household' of the calf. However, difference in temperature is smaller compared to the research.
In practice the energy need will increase with about 10 - 15%. This can be completed by providing 0.5 litre calf milk replacer extra per meal or by raising the Sprayfo dosage of 125 grammes per litre to 140 grammes.
In practice this means a change in the dissolving ratio of 1 kg powder on 7 litres of water to 1 kg powder on 6 litres of water.
If calves are fed with a drinking machine, it is best to raise the amount of litres with 1 litre.

Attention: a change of the dissolving ratio can run the risk of diarrhoea, therefore it is preferred to raise the amount of litres.

Point of attention is the temperature of the milk that will be supplied. This should be warm; about 39°C. Research shows that feeding cold milk (5°C) growth will decrease with 10-15%. This, in comparison with warm milk of 39°C.
Cause: the milk does not need to be 'warmed up' by the calf, by which the animal needs to consume less energy. 
 
In short: when outside temperatures are around or far below freezing point, it is important to raise milk supply with 10-15%, preferably by raising the amounts of litres per day.
Also mind the temperature of the supplied calf milk replacers.