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The aim of incubation: a good-sized, healthy and alert chick like the one on the left. Picture credit: Allens Family Food, Maryland, USA
on June 30, 2009

Research shows benefits of single-stage incubation

Trial results from University of Georgia confirm that single-stage incubation benefits biosecurity and sanitation, and hatching in a commercial broilers.

Single-stage incubation (SS) can be defined as the process of incubating eggs of a single age in an incubator (all-in; all-out), while in multi-stage incubation (MS) eggs are typically placed into incubators at three-day intervals, resulting in incubation of multi-age embryos. With SS, all eggs are removed from the incubator at transfer time, leaving the machine empty. After transfer, empty SS machines can be thoroughly cleaned and sanitised. With MS incubation, only one-sixth (16.7%) of the eggs are removed at transfer. As the machine is never empty, cleaning and sanitising MS incubators can only be superficial.

Single-stage incubation is not a new concept. In fact, the first incubators were designed as SS machines. However, in our fast growing and integrated industry, multi-stage incubation took over several decades ago. At that time, SS incubation was mainly used by parent stock breeders because of the requirement for increased sanitation and the smaller scale of operation. In past decades, SS incubators were fairly small: with a typical maximum capacity of 20,000 eggs, they were inappropriate for large integrators.

In the last decade, manufacturers have increased the size and design of SS machines to rival MS in capacity and hatchability performance. Benefits of SS include better biosecurity and sanitation, more control over incubation parameters (heat, humidity and CO2), less hatchery labour and better quality chicks. With today's concern for food safety now focusing on live bird production, there is more pressure on integrators to reduce exposure to organisms and pathogens in poultry facilities including hatcheries.

Successful use of SS in smaller scale primary breeder facilities provided a good model for this endeavour. Additional pressure has been applied in the last decade to better control the excess heat frequently seen in the genetically altered high-yield breeders. Further, there is interest in increasing efficiency of labour, and SS incubation deserves another look because it addresses these concerns.

This paper reports on a research project to compare SS and MS incubation in a commercial broiler hatchery. Parameters of incubation moisture loss, hatchability measurements and embryo mortality were evaluated. Comparisons of chick quality (SS versus MS) are being conducted currently and data will be published in the near future.

Incubators used in this study

The incubators used in this study were of Jamesway manufacture and were all installed in a commercial broiler hatchery. The SS machines were Platinum P-120 models with a capacity of 120,000 eggs. Platinum P-30 hatchers were used after transfer. The MS machines were conventional Butler incubators converted to Super J models that ranged in age from 18 to 32 years. Their capacity was 90,720 eggs. The hatchers for the MS incubators were Butler machines in the same age range as the Butler incubators.

Numbers and sampling

Eggs were weighed pre-incubation in the hatchery egg room. The eggs were between 1 and 4 days of age at the time of weighing. Each week, one tray per setter trolley (SS and MS) was weighed and marked so that the same trays could be weighed again at transfer. Before the initial weighing, eggs were examined to be certain that no cracked or cull eggs were included in the test trays. The SS incubator has 24 trolleys and 1 tray was weighed from each trolley. For the MS incubator, the eggs from only two trolleys could be compared to the 24 trolleys of the SS. To prevent differences in sample size, several of the MS machines were compared to the one SS machine each week. The number of test trays going into MS machines ranged from 10 to 24 each week, while the test trays going into SS were always 24.

Each week, the same flocks were represented in both SS and MS.

On the day of transfer from setter to hatcher, marked trays were re-weighed to obtain degree of moisture loss. On the day of hatch, two hatcher trays were selected from each trolley (SS and MS). One hundred chicks from each tray were counted and weighed.

Hatchability measurements and break-out analysis

On hatch day, the same two trays used for chick weights (SS and MS) were set aside for break-out analysis. There were always 48 trays of eggs from SS and between 20 and 48 trays from MS to be broken out. In the breakout analysis, percentage measurements were obtained for infertiles, 1st, 2nd, and 3rd week embryo mortality, pipped eggs, cull chicks, farm and transfer cracks, contaminated eggs, cull eggs and eggs set upside down.

The data were used to calculate percentages for fertility, estimated hatchability and hatchability of fertile eggs for each flock.

Technical problems

There were three distinct periods in the study. Period 1 ran from May to December 2005. During Period 1, the SS incubators did not perform well due to a ventilation problem, which caused increases in the percentages of late embryo mortality, pipped eggs and cull chicks. The P-120 was designed to move air in the same way as the smaller model (P-60) but investigators found that the back rows of eggs became over-heated, and hatchability and chick quality were reduced in the trolleys in the rear of the machine. Jamesway engineers studied this problem and made major changes in the P-120 airflow.

Period 2 ran from January to April, 2006. During Period 2, data were collected only in the SS machines to monitor the engineering changes. Consequently, no comparative data were obtained in the MS machines.

Because of the early problems in the P-120 in Period 1 and the lack of comparative data in Period 2, only Period 3 data will be presented in this paper. During Period 3, the incubators performed as designed and the focus of this paper will be on that era. Period 3 ran from May 2006 to January 2007. The engineering changes yielded major improvements in hatchability performance as will be seen in the results.

Moisture loss

The differences between SS and MS in moisture loss at transfer is typical for SS and MS comparisons. Some hatchery managers experienced with MS incubation would be alarmed to have only 9 or 10% moisture loss at transfer as seen in SS. However, hatchability and grow-out results for SS incubation suggest that less moisture loss is not a problem. The difference is due to the damper being closed during the first week of incubation in SS, which results in very little moisture loss during this time.

The important consideration is not the total amount of moisture loss during incubation; it is when the moisture is lost. Obviously, it is important to lose the moisture during the second and third weeks of incubation and not during the first week.

Chick weight

The main reason for the difference (more than 3%) in the average chick weight is that the SS resulted in less moisture loss than MS. This difference may or may not indicate an improvement in chick quality but it does suggest that SS chicks are less susceptible to dehydration post-hatch.

Some incubation specialists feel that due to higher carbon dioxide levels during early incubation, SS hatched chicks are more advanced developmentally and part of the extra chick weight is due to increased development in some organ systems, especially in bone density.


It is obvious from  hatchability results comparing SS and MS that the Period 2 changes to the airflow in SS were beneficial to performance. In Period 1, the MS out-performed SS but the reverse was true for Period 3. Percentages for hatchability, estimated hatchability and hatchability of fertiles were all better in SS.

Although the results show major improvements, Period 3 was not without problems in both SS and MS. In MS, a turning problem caused lower performance during the first hatch in Period 3. Chiller problems in SS hatchers caused reduced hatchability performance on five occasions. Lower performance was seen in embryo mortality due to these equipment malfunctions. The MS turning problem caused higher early and late embryo mortality and the chiller malfunction increased late embryo mortality in SS.

The better performance for SS was even more pronounced after the occasions of hatchery equipment malfunction were taken out. Average early and late embryo mortality was less in SS than in MS in Period 3. There was no treatment difference in middle embryo mortality. Middle deads were less than 0.5% with both types of machine. Percentages for pips, cull chicks, farm and transfer cracks, contaminated eggs, cull eggs and eggs set upside down were all of low percentages and there were no differences between SS and MS.


From the observations in Period 3 of this study, it appears that SS incubation is appropriate for large-scale incubation. The improvements in biosecurity and sanitation in SS compared to MS are well known. This study confirms this and also suggests that moderate improvements can be seen in hatchability performance with large-scale single stage incubation.

Engineer Jerry Garrison inspects the single-stage incubator (Jamesway; Platinum P120)
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