How are chicken eggs fertilized if the male chicks are killed off?

99% of the eggs you buy are ***NOT*** fertile.

Breeding stock is SELECTED & separate.

The vast majority of males...EVERY species....are NOT breeding quality.

In hatcheries ::

Males and females are hatched, vent sexed (if possible), so they can be sold straight run (not sexed) or pullet run (young hens) or cockeral run (young males, these excess ones are often 'packing peanuts', added for extra warmth when shipped) the breeding stock is switched every few years, and usually has a male to female ratio of 1:6 or so. That's the ideal number for breeding pens any ways, it's more of a educated guess.

Breeders ::

The males and females are either

A) sold as eggs

B) sold as day old chicks

C) sold as full or near full grown, so the quality can be shown to see if they are good breeding stock, or pet quality.

The chicks often are never sexed as day olds. Male to female ratios can differ, but usually around 1:6, though often to can anywhere from 1:4 to 1:8, it's up the breeders choice, and some breeds have fertility problems (like rosecomb chicken) so more roosters to less hens. The breeding stock can be switched out every year, adding better quality youngsters and selling the older hens or Roos, or changing up what they are 'covering' (breeding)

Hobby breeding ::

Hardly ever sexed as day olds, often sold as youngsters, around 6 weeks to day old, after that it typically means theyre being kept as pets, but NOT ALWAYS, usually laying hens or pets. Often a large amount are kept for pets, roosters usually sold, unless they have room for more (too many roosters can end up with injured hens). If the Roos are kept, they are sometimes butchered, sometimes pet, sometimes the 'new' roo, or sold for meat/breeding/pet

Hope this helps, roosters are always needed, but some make the cut, some don't. (For breeding that is). It's really the choice of the breeder how the set up is, but really only in hatcheries are the chicks sexed at day old.

Oh and no, hatched chicks are rarely sorted into groups unless at a hatchery ^^

Some roosters are saved just for the purpose of breeding.

Maybe not on every farm, but roosters can be imported in if necessary.

Most farmers are interested in only meat and eggs,

You don't need a rooster for meat and eggs.

So some farms specialize in baby chick production for sale, some farms wnt only hens for food production.

The breeding farms have the roosters, the poultry meat and egg farms most often do not have the roosters.

Lastly, you do not need Roosters for eggs. You need Roosters for FERTILE eggs

There is always a rooster there on the farms for fertilization. They only keep the hen chicks, but re-use the rooster on 'staff' till he's too old to do the job.

Who says there is a "lack of use for them"? A lot of farms keep them for protection, for fertilization, or for meat.