The release of the yolk - the process of ovulation, is the major controlling factor influencing the subsequent steps in the formation and laying of the egg. As a consequence, factors influencing ovulation are of critical importance to the various aspects associated with egg production. The presence of a mature yolk in a follicle causes hormones from the ovary to stimulate the release of luteinising hormone (LH) by the pituitary gland. The presence of LH in the blood stream causes the follicle containing the mature yolk to split along the stigma thus releasing it into the oviduct abdominal cavity adjacent to the oviduct.
Sex maturity
Sex maturity is reached when the hen lays the first egg in her life. While generally sex maturity is genetically controlled, environmental factors play a very significant role. It will be in the age range of 18-24 weeks depending on genotype, but it can be manipulated by controlled feeding practices, light intensity and day length management and other management practices.
Initiation of ovulation
The controlling mechanism setting the time of the day for the first ovulation is not fully understood. However, nervous and hormonal factors are important. Subsequent ovulations are, however, controlled largely by the time of the previous egg passing through the vent i.e. being laid. Subsequent yolk release, if at all, occurs approximately 40-60 minutes after the previous egg has been laid.
Clutches
Eggs laid on successive days are called a clutch. Clutches are separated by days when no eggs are laid. Clutch size is an individual characteristic and may vary in a flock from 2 up to 100 eggs. However, the normal clutch size is significantly less than that and ranges from 3-8 eggs. The larger the clutch size the better will be the total production. Small clutch size indicates an inferior layer and is usually associated with long breaks between them.
Egg formation time
The time taken from ovulation till when the egg passes through the vent varies with individuals within the range 23-26 hours. If the time is longer than 24 hours then the time of laying will be progressively later in the day for each successive egg in the clutch. When eggs are laid at a late hour, an ovulation is missed and the start of a new clutch will be earlier in the next laying day.
Ovulation time
Hens that produce long clutches release the yolk very shortly after first light (whether natural or artificial light). Successive ovulations occur very shortly after the laying of the previous egg. Those producing short clutches usually release the yolk later in the day and often have longer periods between laying time and the next ovulation.
Laying pattern
When pullets first commence to lay their hormonal and other controlling systems have not yet reached a state of balance. As a consequence, the first eggs are laid in a somewhat haphazard sequence. However, once these systems have reached a state of balance (usually after 7-10 days), egg production becomes more regular. Peak ovulation is reached 3-5 weeks after first egg. This will be held for a period and then will decline steadily thereafter until the bird moults or some other factor causes a cessation of production for a period.
