The starter-phase duration for broiler breeders can affect their reproductive performance later, including development, fertility and hatchability, according to a study led by Artur De Freitas Ribeiro, North Carolina State University.
In his presentation at the 2026 International Poultry Scientific Forum, De Freitas Ribeiro noted that “the starter phase is especially important because birds are still establishing metabolic and structured systems.”
The research team evaluated the effects of feeding broiler breeders a starter diet for 4 or 6 weeks on reproduction and investigated the role of targeted body weight, which is “known to play a major role in breeder reproductive efficiency,” De Freitas Ribeiro explained.
The study’s hypothesis was that different starter phase durations, in combination with different targeted body weights, “could influence reproductive parameters…such as fertility, hatchability and embryo development,” he said.
The key takeaway was that a 6-week starter diet, compared with a 4-week starter diet, was associated with higher embryo mortality, independent of targeted body weight.
Study design
The researchers examined two targeted body weight profiles (high and low) and two starter phase durations (4 weeks and 6 weeks). The birds received either starter diets or grower or developer diets. Feed was allocated to control body weight.
In one dark house, 1,600 day-old Cobb commercial broiler breeders were placed in 16 pens and 288 day-old Cobb males were placed in 16 other pens. Each set of 16 pens was divided into 4 groups, each receiving a different treatment.
Lighting was set at 8 hours until 21 weeks of age, then increased to 14 hours with increments to peak according to egg production.
At 22 weeks the breeders were also transferred to the laying house, where seven roosters each were placed in 72 pens.
During incubation, eggs were collected three times a day. Incubation occurred every other week between weeks 25 and 40 for a total of nine times. The eggs were turned four times per hour at first, then every half hour, and every hour for 7 to 14 days, with no turning after day 14.
The eggs were then transferred to a hatchery at 18 days and stored at 57o F (14o C) for 1 to 4 days before being set. Only clean, defect-free eggs were used.
Longer starter phase harmful
The study evaluated fertility, hatchability, hatch of fertile and embryo mortality with the 4- and 6-week starter diets.
De Freitas Ribeiro first noted that “fertility was overall excellent in this study and above the standard” for Cobbs. However, the hens on the 4-week starter phase diet fared better in all categories than those on the 6-week starter diet:
- Average fertility (99.41% versus 98.02%)
- Average hatchability (93.94% versus 92.20%)
- Hatch of fertile (95.15% versus 94.13%).
Hens on the 4-week starter phase also had fewer embryo mortalities on days 1 through 3 (3.31%) versus birds on the 6-week diet (4.23%).
These findings suggest “that changes occurring during early pullet development can have long-term consequences expressed during incubation,” De Freitas Ribeiro believed.
Target body weight, however, “did not significantly influence fertility, hatchability, hatch of fertile or embryo mortality” for either group, he said.
In sum, extending the starter phase to 6 weeks reduced fertility and hatchability and increased embryo mortalities, compared to the 4-week starter phase. Targeted body weight, however, had no measurable effect on reproductive performance.
