Is it ok for a pregnant cow to nurse a calf?

Answer 1

Of course it is! They do it all the time! Dairy cows that are pregnant still give milk until a couple months before they have to give birth again, and beef cows that get pregnant a couple months after giving birth to their last calf (which they're still suckling) still give milk until their calf is weaned at around 6 to 10 months of age.

Answer 2

Not physically. Metabolically, yes it may, especially if there is not enough feed or pasture or feed/pasture quality is low, which would "pull her down" or make her lose condition to the point where she would look almost painfully thin, too thin to be able to have enough condition to give birth to her next calf and produce enough milk for that new calf.