wintering someone else's cows

is there any money to be made from housing someone else's cattle,
i have a 5 bay slatted house and this year i only used 2 of them, i was advised that i should have let the other 3 of them,
i plan on keeping 3 of them for myself for next year and letting the other 2, i'm told that you can earn £1 stg per cow per day, and up to £1.20 for good silage,

my question is how much silage would each type of cow eat,(dry, cow in calf, heifer ect)
a mate tells me that he puts 24 acer of grew out grass into a pit an it keeps 40 head of dry stock with no meal being feed,
this sounds a bit low as it would only take 0.6 acer per beast and i know that my own head of 9 cow's, 1 bull and 6 calf's under 6 month each, are eating less than 5 round bales per week along with 10lb of meal a day,
this works out (roughly, allowing a little for the small calf's) 12 bales of silage for each of the 10 head of stock, over 6 months,
roughly 1 acer per cow and calf

what are your views on this