I have just bought my first 150kg bale yesterday. They told me that a 225kg bale will last 3 horses 1 week and once opened in cold weather will last 2 weeks or 1 week in warmer weather. They said the 225kg bale is the equivilent of 10- 11 shop bought bales. I'm feeding two on it, 1 pony and one very picky horse mixing it with hay to begin with but i should think this 150kg bale should last me 2 weeks, stored in a cold fairly dark place. Hope this helps.
I use the big round bales of haylage and have 3 horses and I can fill around 50 haynets up out of each one, so depending whether they are in or out is how long they last.
I have the 4ft big bales and one lasts my 3 around 7 - 10 days. They live out and get a pile each am and pm. Don't hav a problem with it going off. Works out so much cheaper.