Still no calves here, but I'll give it a couple more days.
Could they be affected if they run out of food? Every morning I find their trough empty. I just have such a difficult time keeping it filled, it takes at least 50 carrots to push the bar up 1/4, and that's gone within half a day. My chickens, on the other hand, have not required a refill for an entire
week, and I never filled their coop beyond 3/4 to begin with.
I try to fill it up as much as possible before I go to sleep, but I can't always immediately rush back to feed them again the next day.

In this space of time, I've milked about 20l of decent quality milk from the nearby plains herds using clovers. I'm beginning to think that is a much more reliable way of obtaining milk, without my game becoming a 24/7 struggle against keeping the trough* full!
*Edit: Not troughs, it's hard enough with just one. xD