Have you turned cows out onto pasture yet or are you looking out on either snow covered or sodden soils.Not only are some soils still very wet but the soil temperatures across the UK, Northern Ireland & Brittany in France are all below average for this time of year. Soil temps are between 2 & 4 degrees C when they are often 5-6 degrees C by now.
Whatever your situation you need to do a farm walk & not only measure the grass but assess how the pastures look. The winter kill caused by frost & snow damage has been substantial on many UK dairy farms this winter. Some dismiss winter kill as an inevitable consequence of winter frosts & wind.
However as everyone starts to measure the pasture covers now....we are starting to get some idea of the magnitude of the losses. Many farms are reporting average pasture covers this spring that are 3-400kgs DM/ha less than the closing covers last autumn. A bale of silage is approx 200 kgs DM. So some farms have lost the equivalent of two bales of silage per hectare. This is approx £20-50 per hectare....so a farm loss of feed amounting to say £3000-7500. No small loss! . 
Most of the damage was caused by the January snow & the cold spell where frosts were common in most areas of the UK. Older pastures (low fertility species) & those not recently fertilized with nitrogen seem to be more susceptible.
Many pastures on organic farms seem relatively unscathed compared to their conventional neighbours (maybe the soil N is high due to summer clover N). 
Winter kill is a mix of physical damage mainly to older leaves & some fungal or mould development which seems to kill off the leaves. The roots & crowns seem to recover. Pastures less affected are just showing the "purpling colour" of frost damage.
So how bad is the damage? Pasture plate meter readings at the end of autumn 2009 on many farms were very high. Instead of the normal 2000-2100 kgs DM per hectare average farm cover, some farms had say 2500 average with individual paddocks well above 2800kgs. These are the pastures that appear most affected by winter kill. Many of the farms that are being monitored regularly were the ones with extraordinary covers in November. Why? Do we have short memories about winter kill of pastures? Was the money invested in monitoring during the year completely lost when you assess the pasture DM losses due to winter kill? Or did these farms take their eyes off the ball not fully realising the potential for losses?
What do you need to do now? I think the worse affected fields need to be grazed asap with either stale cows or dry cows.
It's not great feed but it is better to be grazed early. A grazing minimises the plant disease risks & then allows N fertilizer or muck to be applied depending on your NVZ status. The worst affected pastures may need reseeding but let's hold off on that decision until you view the recovery after grazing.
What are the lessons?
Graze all fields at least once after the first week of October.
Aim to close grazing with an average cover of between 2-2100 with the longest pastures not exceeding 2600 kgs DM/ha.
Don't use grazing recipes taken from a different country with a different winter climate. i.e. a third of the farm must be grazed by a certain date etc. etc.
Use N as late as you are allowed (NVZs) to get good fresh growth in late autumn & to take advantage of any "anti Freeze" affects of N fertilizer.
It's important to get good residuals i.e.1500 on that last grazing....often this is difficult if it turns wet.
I guess this experience this year does also questions the need for a pasture wedge after the last grazing? It's not common practice on some of the best farms in Brittany!
What do you think?
Lastly!
Don't try to use a plate meter to plan & arrange grazing management until say mid March. The plate readings are usually very unreliable!
Instead use the 'Spring Rotation Planner' a highly effective but very simple excel spreadsheet. If you don't have a copy email me.
The second reason I think calf rearing is so important is that there is very good evidence that the weaning weight has a huge influence on heifer weights at mating & at first calving.The Heifer Liveweight Targets need to be set at 90% of mature cow liveweight at first calving. Calves that struggle during the milk feeding stage prior to weaning seem to struggle up to 15 months & often calve down under weight.These heifers then under produce in the first lactation as they are still growing....the risk of not getting back in calf is substantial.
