In New Zealand cows are kept outside 365 days of the year.  During the winter when the grass growth is very slow we have to conserve as much pasture/grass as possible for the coming spring when the cows calve.  In order to do this the cows are given an alloted  feed allowance that meets only the needs of their maintenance, pregnancy & any liveweight gain that they might require.  At the moment we have our cows split into 3 "mobs" , 2 of the mobs are on a ration of swedes and grass and the other on a ration of silage and grass.  This picture shows one of the mobs  on their daily grass "break" (a break is an alloted part of a paddock sectioned off by temporary electric fences)