[Raine-chime]

Most dairy farmers breed their heifers to freshen/calve at 2 years old. With a 9 month gestation, that means you breed them when they are 15 months old.

In our area, you can rent a beef bull to use when your heifers are old enough. IMO, beef bulls crossed with dairy heifers give you the best of both worlds. Their heifer offspring produce lots of milk and raise good calves. Their bull offspring have enough of the beef in them to grow well for meat.

Many beef breeds cross well with Holsteins. Hereford or Black Angus are both usually readily available and are both very good choices.

Have fun with your heifers. You will have lots of milk when they have their calves.