Pre-calving Jersey food restrictions

I am getting two in-calf Jersey cows from a local dairy farmer who puts in 90 new Heifers each year and takes out the worst 90 (empties first but then others are chosen).  He is drying them off now, and they should calf in about 6-8 weeks.  I have had an especially wet summer and mild autumn (in New Zealand), and so there is green grass still growing everywhere - probably enough to last the winter.  I have been told to restrict their calories before calving or milk production will be reduced.    This will be hard to do in practice on my pasture.  How important is this?  What sort of milk loss am I looking at?  I guess most people live there is not green grass available through winter, so this is usually not an issue.  I don't expect my pastures to maintain peak milk production yet anyway this coming year.  I plan to build in some perennial high-protein fodder plants next spring.

I should maybe add that it is typical NZ dairy cow that has spent its life on green pasture, but has also had some supplementation - mainly copra meal I think.

Hi Annie, Hope this isn't too late to be helpful!
Here in the States, when we talk about restricting dry cow diet, we mean cut the corn silage and grain and put her out on pasture. Obviously you Kiwis have a better sense for pasture in the first place, and I don't know exactly how it grows there, but I wouldn't be too worried about some green autumn grass, although the spring flush might be too much. Restricting a dry cow diet helps prevent ketosis when they calve so is always wise. But then at two weeks before calving, you usually want to slowly start improving their feed, a "rising plane of nutrition" through calving and the first few weeks thereafter. What you DON'T want to do is the opposite: nice green grass while she's dry, then switching to dull dry hay just when she calves. Calving and the transition to lactaction is a big metabolic shock and they need something to draw on to get through it.

DO give oral calcium supplements when they calve, especially as these are Jerseys. Here that would be in the form of a tube of calcium paste, shove it down their throats and squeeze the paste out. She'll need one the day she calves and another 18-24 hours later. This prevents milk fever, which Jerseys are known to have trouble with, especially as they get older. If you catch that early, it's not too bad, but if it develops until she actually collapses in paralysis, you generally have to get the vet out for an emergency IV hit of calcium straight to the veins. Much easier just to feed the tubes.