ive always wondered the same... or, when switching Roo's or segregating a pair of birds, how long does it take to ensure the new rooster is the fertilizer?
Good fertility remains up till 2 weeks after removal of the rooster. Some fertility may last up until 4 weeks after his removal, but it is generally felt that 3 weeks after removal is the "cut off" period.
I know dad had hens removed from roosters for 3 weeks, and i still hatched their eggs...so know 3 weeks, but b4 adding another rooster he alway waited a month.