[peterwaite]

I am about to begin my poultry keeping project. I only wish to keep hens but would like , at some time, to have chicks. If I choose to "borrow" a cockerel, a) how long would he have to spend with the hens before their eggs become fertile? and b) once the cockerel was removed, how long would the hens continue to provide fertile eggs?

[Kate and her Ducks]

Don't know about chickens but in ducks they are fertile pretty much as soon as they start mating. I hear they can remain fertile for up to 3 weeks after the male is removed but I haven't tested this out. The other option is to buy fertile eggs and put them under a broody. Saves the stress of introducing a cockrel to the hens.
Sure someone in the know will be along soon and welcome to the forum. They're great to us newbies.

[Foxy]

I wouldn't of thought it would be very practical to borrow a cockerel, getting him settled, used to the hens etc. Are you able to keep a cockerel yourself? If you are able to borrow one you would need to make sure he is old enough, very fit and healthy and your hens ideally at least a year old.
A cock would fertilise  the eggs as soon as he starts treading the girls. Then after removing him from the pen the eggs would remain fertile for about 3 weeks.

[ness]

I agree with the above posts.  I reckon your best bet would be to include in your choice of hens a breed that are prone to broodiness (silkies, pekins etc).  Then source some fertile eggs locally and put them under the broody.