TechFocus_EGGS 0325 - Late-Stage Incubation Temps, Optimisi…

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Late-Stage Incubation Temperatures: Optimising Broiler Chick Quality By Chris Murrell, Hatcheries Manager & Hatchery Specialist, Cobb Europe

Incubation is a delicate balancing act of temperature, humidity, and ventilation—variables that change in importance as the embryo develops.

Although much attention is devoted to the incubation stage (0 to 17 days), the final period in the hatcher (18 to 21 days) is equally critical. During this period, embryos undergo substantial physiological transitions, including yolk sac absorption, bone mineralisation, and the reorientation necessary for pipping. Because of these complexities, it is crucial to monitor actual eggshell temperature (EST) rather than relying solely on standard air-temperature setpoints. Why Late-Stage Temperatures Matter As mentioned, during the final stage of incubation, the developing embryo is rapidly absorbing yolk, mobilising bone minerals, and generating significant metabolic heat. If conditions in the hatcher do not allow proper heat dissipation, stress levels rise, and quality suffers. Research consistently demonstrates that maintaining an EST between 98.5 to 99.5 °F (36.9 to 37.5 °C) during this period optimises chick quality (Maatjens et al., 2016; Sözcu et al., 2022). Conversely, higher temperatures, particularly above 102 °F (38.9 °C) correlate with reduced chick quality and poorer post-hatch performance (Sözcu et al., 2022). The Challenge of Monitoring the Hatcher Despite its importance, the hatcher stage often receives less monitoring attention than the incubator. This happens for several practical reasons: • Opening hatcher doors disrupts temperature and humidity • Eggs are more difficult to handle in the upright position • Chemical treatments and other sanitation practices can complicate measurements • Time constraints during the busy hatch window

However, periodic EST checks (even if only a few times per flock) provide valuable data for hatchery managers to fine- tune temperature profiles based on: • Flock age • Breeder flock characteristics

• Egg storage duration • Breed-specific needs

The benefits of proper monitoring outweigh the challenges, especially when considering the impact on final chick quality. Balancing Hatch and Quality Historically, hatchery managers have focused solely on achieving good hatchability. Since higher-than-optimal temperatures can achieve this goal, they may not pursue further optimisation for quality. However, internal trials on Cobb eggs show that maintaining 98.5 to 100.0 °F (36.9 to 37.8 °C) EST yields better chick quality than higher temperatures such as 101.5 °F (38.6 °C) EST. Applying optimal hatcher temperatures helps ensure that chicks do not emerge weak, dehydrated, and lethargic, optimises the number of saleable chicks, and helps prepare chicks for growth performance and low mortality through grow out. Hatchery managers sometimes worry that reducing hatcher temperatures might delay chicks. However, minor temperature adjustments have minimal impact on hatch timing. A reduction of approximately 1 °F in eggshell temperature (EST) between 18 to 21 days typically only extends incubation by a few hours. This is rarely problematic in practice, as most hatcheries build buffer time into their schedules, typically setting pull times earlier than the

Figure 1. Temperature Effects on Hatch Performance and Chick Quality

Data from a single unpublished internal trial, for reference only.

absolute minimum required for complete hatching.

Internal trial data demonstrates the advantages of maintaining lower eggshell temperatures (EST) during the hatch phase (Figure 1). At 98.5 °F (36.9 °C) EST, we observed a slight increase in Hatch of Fertile (+0.21 %) compared to 100 °F control, and a reduction in both B grade (-2.27 %) and C grade (-0.92 %) chicks. The contrast becomes even more pronounced when comparing 98.5 to 101.5 °F EST, with a 0.66 % improvement in HOF, 9.7 % fewer B grade chicks, and 1.19 % fewer C grade chicks at the lower temperature. These findings suggest that maintaining EST from 98.5 to 100 °F (36.9 to 37.8 °C) provides optimal results. Our data aligns with findings from Sözcu et al. (2022), that reported even moderate temperature increases to 100.8 °F (38.2 °C) during late incubation resulted in reduced hatchability, increased late-term embryonic mortality, and poorer chick quality. Likewise, Maatjens et al. (2016) found that an eggshell temperature of about 98.5 to 99.5 °F (36.9 to 37.5 °C) during the last week of incubation led to superior chick quality metrics and enhanced first-week performance relative to higher temperatures. It’s important to note that these eggshell temperatures represent averages measured in controlled trial conditions. In commercial incubators, temperature variation and hot spots are inevitable. Given this natural variation, our findings suggest that targeting the 98.5 to 100 °F (36.9 to 37.8 °C) range, rather than 100 to 101.5 °F (37.8 to 38.6 °C), provides better insurance against quality issues. Targeting the slightly lower range acknowledges the reality of temperature variations while optimising both hatchability and chick quality. Tell-Tale Signs of Overheating in the Hatcher 1. Urates Inside the Egg When chicks are exposed to higher-than-optimal

Image 1: Urates inside the egg

temperatures, their metabolism accelerates, and they may excrete excess uric acid before fully using yolk nutrients. The excess uric acid appears as urates within the shell after hatching. 2. Early Hatching, Weak and Lethargic Chicks When embryos are exposed to excessively high temperatures, their metabolic processes accelerate, causing them to develop and hatch earlier than expected. Early-hatched chicks from overheated eggs typically appear weak, lethargic, and less alert compared to chicks incubated at optimal temperatures. 3. Red Hocks and Beaks When hatcher temperatures are too high, embryos increase blood flow to their extremities (like hocks and beaks) to dissipate heat. This causes visible redness. Additionally, overheating can make chicks more active inside the shell as they attempt to reposition or cool themselves, rubbing against the shell at contact points. These physical and physiological responses are indications of heat stress and warrant better temperature management in the hatcher. 4. Dead Pipped Chicks Pipping is an energy-intensive process. If the environment is too hot, chicks can become exhausted, dehydrate quickly, and fail to progress from external pipping to complete hatch. High temperatures shorten the time when

the chick can sustain pipping efforts, often leading to mortality. 5. Higher Residual Yolk Sack Weights Elevated temperatures during late incubation disrupt embryonic development by increasing metabolic stress and impairing yolk nutrient absorption. Under heat stress, embryos prioritise thermoregulation, reducing their ability to efficiently process yolk-derived lipids, proteins, and antibodies. This often results in higher residual yolk sac weights at hatch—up to 15 % of chick body weight compared to the ideal range of 6 to 10 %— which correlates with slower early growth rates and compromised immunity. Residual yolk sac percentages naturally decline post- hatch as chicks metabolise remaining nutrients. While immediate post-hatch weights may be higher due to retained yolk, the efficiency of yolk absorption depends on several factors: • Hatcher Conditions: Poor ventilation (elevated CO₂ levels) and humidity extremes can slow yolk absorption. Higher eggshell temperatures (EST) accelerate hatching but increase the risk of incomplete yolk use if chicks are processed prematurely. Additionally, late-stage heat stress reduces the transfer of yolk-derived carotenoids, causing pale down feathers. • Feed Access Delay: Chicks held for more than 24 hours post-hatch deplete their glycogen reserves, increasing reliance on residual yolk and potentially exacerbating growth delays. The first four chicks seen in the Table 1 fall within the ideal range. In contrast, the last two chicks display high residual yolk levels, exceeding the optimal 6 to 10 % range. Chicks exhibiting elevated yolk sac percentages and black button navels, indicative of late-stage incubation issues. The accompanying navel photograph illustrates severe cases where the navel is prematurely forced closed around the yolk sac before complete absorption.

Image 2: Black button navel

Practical Tips for Managing Late-Stage Temperature 1. Measure EST Directly • Use an, ear thermometer or probe logger on confirmed living embryos • Sample eggs systematically from top, middle, and bottom trays, front to back • Monitor temperature variations across positions - wide variations may indicate airflow issues • Continue EST measurements until approximately 20 days and 12 hours of incubation

Table 1: Chick weight and yolk sac percentage

Chick Weight (g)

Yolk Weight (g)

Yolk Sacks as % of body weight

39.7

3.5

8.8 %

40.5

7.4 %

40.5

3.5

8.6 %

41.5

9.6 %

46.4

12.9 %

44.1

7.1

16.1 %

Image 3: Well healed navel

Image 4: Red beak

Image 5: Perfect beak

Image 6: Red hocks

Image 7: Perfect hocks

References Maatjens, C. M., van Roovert-Reijrink, I. A. M., van den Anker, I., Engel, B., van der Pol, C. W., Kemp, B., & van den Brand, H. (2016). Temperature during the last week of incubation. II. Effects on first week broiler development and performance.

2. Adapt to Your Specific Context • Different breeding flocks and egg sets have varying metabolic rates so temperatures will vary • Standard temperature profiles may need adjustment between flocks • Each machine manufacturer has unique ventilation characteristics, affecting the relationship between air and eggshell temperatures • Fine-tune based on your EST measurements rather than following fixed profiles 3. Monitor Quality Indicators and Watch for Stress Signals in Hatch Residue: • Red hocks and beaks • Unabsorbed yolks • Navel quality issues • Elevated late mortality rates • High percentage of dead pipped chicks • Urates • Early hatching chicks Conclusion Late-stage incubation plays a decisive role in broiler performance. By monitoring and maintaining optimal eggshell temperatures (98.5 to 100.0 °F or 36.9 to 37.8 °C) in the hatcher, managers can significantly improve chick quality and reduce common issues like red hocks, increased black button navels and unabsorbed yolk. While this requires careful measurement and fine-tuning, the benefits - including better hatchability, fewer downgrades, and improved broiler performance - it is a worthwhile investment towards success.

Poultry Science, 95(9), 2136–2144. https://doi.org/10.3382/ps/pew145

Sözcu, A., A. İpek, and H. van den Brand. 2022. Eggshell temperature during early and late incubation affects embryo and hatchling development in broiler chicks. Poultry Science. 101:102054. https://doi.org/10.1016/j.psj.2022.102054

About this author Chris Murrell graduated with a degree in Business and Economics and began his career as a Graduate Management Trainee in Breeders and Hatcheries. He has gained valuable experience managing several broiler hatcheries, including the largest hatchery in the UK. For the past seven years, Chris has worked with Cobb Europe, where he has managed Pedigree, GGP, GP, and PS Hatchery operations across Europe. He also supports hatchery teams in the EMEA and Asia regions as a Hatchery Specialist, providing technical guidance and support. In addition to his experience in the poultry industry, Chris holds a Master of Science degree in Computer Science and Data Analysis.

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