Clarified Chicken Mating for Confused Chicken Keeper

[Eelantha]

Please excuse my general confusion and equally confusing post, but I had to ask this.

A recent conversation about hatching rate and fertility issues on another thread has made me realize there seems to be two contradictory facts circulating on the web. On one side, it's clear some heritage breeds of chickens have 50%-60% fertility/hatch rates, and on the other, everyone knows that hens can preserve rooster sperm inside their bodies for up to three (sometimes four) straight weeks.

If a hen can keep the sperm viable for that long, how comes only half the eggs she will lay in the next three weeks will prove viable and hatch chicks? Shouldn't the sperm fertilize every egg she will lay in that amount of time without problem? Or does it stay in some secluded spot or pocket inside her cloaca that I'm unaware of, and does not always manage to fertilize the yolk in time before the shell grows around it?

Basically this chicken keeper does not understand how half the eggs placed in an incubator wind up duds, when there's clearly enough sperm provided by the rooster to ensure a thorough fertilization of all the eggs laid by the hen. What am I missing here?

 

[sourland]

Some roosters have low sperm levels and/or sperm with low motility.

 

[Erba]

Old roosters also do not fertilise eggs very well.

 

[Eelantha]

@sourland - low 'motility'??

@Erba - It only takes one successful mating out of many attempts to get the sperm stored and viable inside the hen for the next three weeks. Unless the rooster is 100% sterile, it is impossible for him to fail at his job with how often he mounts his hens in a day, especially if they're low in numbers (1,2,3 or 4 girls). If half the sperm is non-viable because of low vigor or fertility issues, there is still the other half that is very much alive and fertilizing the yolks. So why do half the eggs laid by the hen still wind up duds despite there being viable sperm (no matter how little) to ensure those yolks become embryos?