Sorry, not speaking for everyone else, but my cows I bought with those genetics have no problem with calving but were not the best milkers. It's better to you use them to flush and have a good recip raise the calf.
When you say not best milkera you mean cant raise one or just calf is a little behind at weaning? What where they like on bottom side one i just bought has shorthorn on bottomw side.
Udders didn’t have as much milk as other cows and calf would have developed slower if left in pasture but I brought him closer to barn to give him feed early. Need special care and creep feed early