Roosters will only fertilized eggs when they are sexual mature. Fertilizing is not necessary for egg production but is required for hatching chicks. The fertilized egg has a slightly different appearance than the unfertilized egg but it has limited effect on the taste or nutritional value. Roosters fertilize by mounting the hen and depositing semen. The hen stores the semen until an egg begins to form. The egg is fertilized before the shell develops.
Fertile vs. Infertile Eggs
Fertile eggs are desired for hatching chicks. Hens will produce eggs without the help of a rooster but the eggs will never hatch a chick without fertilization. The fertile egg is identified by the round, white dot known as a blastodisc. The small dot is prominent and has a perfect round shape in a fertilized egg. Fertilized eggs also show some red coloration after a day or two of incubation. The infertile egg has no red coloration and the blastodisc is uneven and less prominent.
Number of Roosters
Limit the number of roosters in your flock to encourage fertilizing without too much competition. Some roosters will take a secondary roll in the flock when dominated by other roosters. Old, infertile roosters also will dominate fertile roosters and your eggs will not produce chicks. One rooster for every five chicks is the maximum for fertilizing without competing. Fewer roosters is acceptable as well. A single rooster will manage 10 hens without any issues.
Age of Roosters
Like hens, old roosters will lose fertility. The roosters will continue breeding but the attempts are unsuccessful. Many roosters live for more than a decade but fertility often decreases around 7 years of age. Roosters on a natural diet will remain fertile longer than roosters eating a calcium rich commercial laying feed. Monitor the hatch rates of your eggs and cull older roosters from the flock when they stop producing.
Create a comfortable environment to encourage breeding. Flocks threatened by predators and unsanitary conditions are less likely to breed successfully. A healthy flock will breed with very few issues. Keep your roosters and hens together at all times so they set the pecking order. The rooster will take charge of the hens and breed at will. Keep them in a safe run with dry bedding, roosting bars and a healthy diet mixed with natural forage, table scraps and commercial feed.