Jersey cows are very prone to milk fever if heavy milkers (I think I used to treat 1 in 3 or 4 of our herd when I used to milk them) so I would be reluctant to rely on pasture at peak yield time if you are expecting them to multi suckle ...
Totally, that's why Hillie's on dairy nuts at present, as she's feeding two. Katy will get dairy nuts if she looks to need them, when I switch Hillie's foster calf onto her when she calves in a few weeks' time. I've just got a pre-calver lick in for her.
They'll be rearing three between them, with me milking a little for us, for a few months, then the plan is that in March, we spean Hillie's own calf (who will then be 7-8 months old) and the shared foster and start a milking rota. After that, each Jersey will rear her own calf to 5 months or thereabouts plus give us milk for ourselves. We hope to make yoghurt, cheese, ice cream and so on.
Once we're on that regime, I will be looking to manage production and condition, if I can, to have them produce well but not excessively, and carry enough flesh for us not to think they look like hat racks! I know it can be hard to keep condition on lactating Jerseys, but we can manage demand by how much we take, so should be able to do it, I hope, and feed grass or Lucerne pellets, so that their diet is more natural and they have to work a little less hard. Maybe they might need diary nuts for a month or two or three, as their own calf gets to peak demand; we'll just have to see. Christine says she always wishes they'd carry a little more condition too; we would like to arrange a visit to Smiling Tree Farm and I will be interested to see what condition her girls maintain.