In the depths of winter there have been 20 consecutive days with at least 20degC frosts.
Trevor Heaney, who farms Ben Nevis Station, told last week's Federated Farmers' South Island high country committee two-yearly field day in the Central Otago valley, that while the country was clean and wool bright white, production tended to be lower.
The Ben Nevis pastoral lease at the northern end of the valley covers 14,500ha, from 500m above sea level to 2000m on the Remarkables.
Of that, Mr Heaney said 7000ha was above the snow line and not grazed.
Winters tended to be long and spring could be slow, with average annual rainfall of 750mm.
Pioneer Generation bought Ben Nevis and the neighbouring Craigroy Stations in 1997, for the possibility of building a hydro-electric plant in the valley.
It was in the process of taking the properties through tenure review.
Mr Heaney said under the proposal, 10,500ha would go to the conservation estate and 4000ha to freehold, 2000ha of that oversown and topdressed.
Don Clarke, from the neighbouring 9600ha Carrick Station, said other issues facing valley and surrounding hills farmers were rabbits, keas and open gates from tourists travelling wherever they liked.
As a result of the keas, he vaccinated wethers annually.
The confident, inquisitive birds land and ride on the back of sheep and to encourage the sheep to move, they peck their back.
This can spread sheep-killing disease, especially if keas have eaten carrion.
Carrick Station ranges from about 800m to a top of 1750m close to the point where Carrick, Nokomai and Glenary stations meet.
Mr Clarke runs 10,500 merino sheep, 500 deer and 230 cows, producing 45 tonnes of fine wool, of which 26 tonnes went under contract to Icebreaker.
His 3000 wethers mostly lived on the hills and faces overlooking the Nevis Valley.
Mr Clarke ran 70 cows on the faces.
He put 4500 ewes to the ram each year, with ewes mated for the first time as four-tooths.
The balance of Carrick means Mr Clarke left his ewes on the hill until June or July when they were brought down to paddocks around the homestead and fed baleage.
Mr Clarke said the property was going through tenure review, which could see 3000ha going to conservation, land on which he grazes his wether flock.
At the valley's southern end, the 6000ha Kingston Station reaches from the Kingston township, over the Hector Mountains and into the Nevis, where the Taylor family runs 3500ha.
Tim Taylor said they ran halfbred and Wairere Romney ewes and Hereford and Angus cattle, but the valley was vital to allow land nearer to the homestead to be spelled before winter.
Mr Taylor said not having access to the Nevis would mean reduced stock numbers and selling lambs as store at weaning.
Kingston Station rises to 1600m above sea level.
In winter the Taylors open it to heliskiing and a snow cat operator, but the valley road gave trampers and hunters easy access to the mountains at other times.
Mathew Taylor, of the 5500ha Lorne Peak Station, relies on the station's 2000ha in the valley to spell lower country and to allow lambs to be finished on other parts of the property.
Lorne Peak runs 9000 halfbred and Romney ewes, 350 cows and 1000 rising one- and two-year cattle.
They winter-graze 3000 dairy cows.
Mr Taylor estimated that without access to the valley, stock ewe numbers would be back by 1000, with 50 to 60 fewer cows.
The 150th anniversary of settling Nokomai Station is next month.
Owner Brian Mr Hore said the rest of the 38,000ha property was vital to its future.
Over the years, 20,000ha was oversown and topdressed, an example of how most of the property was utilised.
Mr Hore said the farm had undergone a natural area protection survey which found rare bogs.
Mr Hore would never drain them and had excluded cattle and motorcycles.
He was happy to protect those areas with a covenant.
He had previously run 16,000 wethers, but dropped them due to the cost of replacement, low returns and a kea problem in the Nevis.
Mr Hore said in a two-year period he lost 700 wethers to keas.
Mr Hore now runs just under 20,000 ewes and 8000 other sheep on Nokomai, with numbers fewer than traditionally were run, due to restructuring which had seen two properties previously run as part of the main block being split off as separate units.