Every dairy cow is different.
Remember, they are athletes. Just as you see extreme runners with little to no body fat, you will see, at the height of performance, some dairy cows keep little fat on the topline. This isn't true of the low producers (which I do prefer), but cows giving many, many gallons of milk a day will usually appear quite thin to the general public.
Comparing the body of a beef bred cow to a dairy type cow isn't comparing apples to oranges, really.
Now, it is true that dairy cows can be too thin because someone isn't giving proper care, but it is also true that high production cows can milk so much, they cannot consume enough safely to keep a condition we would like to see during their peak.
I'll go over my person cows over the years under each photo as you scroll through, explaining age, their situation and what they were fed.
I always recommend searching the National dairy shows around the globe to get an idea of what extremely productive cows often worth tens of thousands (or more) dollars look at at peak production and when being shown to better understand dairy cow weight, for instance: https://www.facebook.com/cowsmo/photos/pb.21100185898.-2207520000.1454346181./10153222572345899/?type=3&theater
Always look at coat condition, overall bright eyed appearance and whether the abdomen appears healthy even if the topline is thin. . .when deciding on health of the animal.
Some additional insight on body scoring dairy cows:
I will note here that Dairy goats are different. They are generally able to keep a high body score even in milk, unless they are extreme producers.
|Our first dairy heifer. This is Stella (she isn't wearing that halter, John just had it around her nose, not hooked to hold her still) at 9 months old. Obviously, she wasn't bred at this age. This is a dry heifer at a body score of about 4|
|This is Ellie. Ellie is an 8 year old Mid- Mini Jersey. She is about 10 montns into lactation. She is a body score of 4.5 here. She is a low production cow who receives and needs no grain while in milk.|
|Elsie again, but here she is 6 months into lactation.|
She is a 3.0 in this image, and she was giving about 1/2 as much milk, so her ration was lowered to about 10 lbs of grain daily.
|This was Anya. She was about 5 months info lactation here just raising her bull calf. We did not milk this Dexter cow, but she was grass fed only. She is about a 3.25 in this image.|