In the UK, most dairy cattle are produced by crossing a Friesian cow with a Hereford bull. You can tell the hybrid cows coz they have a white patch (a Hereford feature) at the top of their face. The heifers go on to be good milkers (as good as a pure-bred Friesian?) and the bull calves can be reared for low grade beef - burgers, I suppose. (Proper (i.e. tender & yummy) beef needs proper beef strains like Aberdeen Angus or Charolais).

If pure-bred Friesians are used (and I have my doubts about this sex-selection AI business!) the bull calves are slaughtered at or shortly after birth coz they're virtually inedible, and not worth raising.

The above is my understanding of the situation, based on approximate academic familiarity with it over the last 20 years or so. I may well be out of date and am quite prepared to be corrected by someone who really knows what they're talking about!

Fish stocks have been depleted by overfishing partly for food species, but also for fish to turn into fishmeal for animal feed (for supposedly herbivorous cattle!) and even for fertiliser!!

Enjoy your dinner!

Steve