Basically agree with
@Dsth .... couple of things to think about... When do you want a calf? Are you going to milk her or just use her as a nurse cow? Since you seem to be in the area where there are dairies, getting some calves to put on her should not be a problem.
Breeding will depend not only on her age and size and condition... but when you want a calf... I personally do not want my nurse cows to be calving in the bitter cold... It is hard enough to get calves started, especially on an unproven dairy animal... some will NOT take to being a nurse cow unless they are tied/locked into a stanchion type situation.... and the calves also feel the cold... the cows teats can get sore/chapped/ and that can be an issue... I want to start calves in late march through about Nov here... so I definitely will not be breeding cows from Feb through early June...
DO NOT TAKE THIS WRONG........No matter how POORLY you feed a dairy animal, thinking they will not produce as much milk... a dairy cow cannot just feed only one calf... the genetics are there to make alot of milk... even a low end dairy cow will make 40-50 lbs a day... so at least 5-6 gallons... when first fresh. She will HAVE to be milked and/or have SEVERAL calves on her or she will get mastitis...
What I am saying is you will not be able to "control" her milk production by feed alone because she is BRED to make milk.... Yes, she will peak at a lesser amount, and the milk will fall off quicker... BUT..... when she first comes fresh, she will make buckets of milk and she will drop weight and lose condition and not cycle back or come back in heat or anything... if she does not get enough feed. Dairy cattle will "milk the fat off their back" for the first 120 days.... and so they have to get fed enough to keep them milking and to get back into condition for all their body functions, like uterus getting back to normal size, and then cycling, to get back on track.
I am thinking that in another thread, you were talking about grazing her... and that is all well fine and good... there are lots of grass based dairy's.... but they feed more than just grass... the cows can get some sort of grass silage... known as haylage.... or other supplemental feeding..high quality alfalfa and other "grass" type feed; because grass alone will not cut it for a dairy animal. PLUS... if she calves in the 2-2 1/2 yr old range... she will still grow for another 1-2 years... so she needs all the nutrition she can get to finish growing and mature.
That part is the same with beef animals... they get calved out around 2 or so.... and on the best pastures, can feed one calf and continue to grow and then also cycle and get pregnant. BUT, they are only making maybe an average of 1-2 gallons a day... they are not bred for "making milk" like a dairy animal...They will hopefully be "fatter" when they calve due to their build/breed..... and will gain weight more easily than a dairy animal on just grass pasture... and generally they will not make more milk than their calf can use overall... totally different type of handling especially in the early part of lactation.....