Gram Research analysis of a 2026 study with 840 broiler chicken eggs found that warming eggs during incubation lowered hatchability from 95.7% to 87.7%. The same study suggests that a probiotic and prebiotic feed supplement helped normally hatched chickens grow better, while its benefits shifted toward stronger leg bones in chickens from warmed eggs.
Gram Research analysis of a 2026 study in the British Poultry Science journal looked at how heat exposure during incubation affects broiler chickens. Researchers warmed some fertile eggs slightly above the usual temperature for one week before hatching. Chicks from warmed eggs hatched less often, and they ate less feed early on. Later, a probiotic and prebiotic feed mix called a synbiotic changed what the birds gained. In normally incubated chicks, it helped them grow and absorb nutrients better. In warmed chicks, it mainly strengthened leg bones. The study tested 840 eggs in a hot climate, where chickens often face heat stress. The findings suggest that hatchery conditions and feeding plans should be considered together.
Key Statistics
A 2026 study of 840 fertile Ross 308 broiler chicken eggs found that warming eggs during incubation lowered hatchability from 95.7% to 87.7%.
In the same 2026 study, adding a synbiotic at 1 gram per kilogram of feed increased body weight gain in chicks from normally incubated eggs.
The 2026 study also found that footpad dermatitis and hock burn scores rose only in synbiotic-fed chickens incubated at the standard 37.5°C temperature.
The Quick Take
- What they studied: Does slightly warmer egg incubation change how well chickens respond to a probiotic and prebiotic feed supplement, and how does this affect growth, gut health, and leg strength?
- Who participated: 840 fertile Ross 308 broiler chicken eggs were divided into groups. Some were incubated at the normal temperature and some at a slightly higher temperature during the middle of incubation. The resulting chicks were raised in a tropical setting, and some received the feed supplement.
- Key finding: Warming eggs during incubation lowered hatchability from 95.7% to 87.7%. In normally incubated chicks, the feed supplement increased weight gain and gut villus height, which are the tiny finger-like structures that help absorb nutrients. In warmed chicks, the same supplement increased phosphorus in the leg bone, a mineral that helps bones stay strong, but reduced gut villus height.
- What it means for you: The results suggest that how eggs are incubated can change whether a feed supplement helps or does little. This is mainly relevant to poultry producers and hatcheries. Results came from one study on chickens in a hot climate, so the same effects may not appear on every farm. Consumers do not need to change their own diets based on this study.
The Research Details
Researchers started with 840 fertile chicken eggs of the Ross 308 breed, a common meat chicken. Half were incubated at the standard temperature of 37.5°C. The other half were warmed to 38.5°C from day 8 to day 14 of their roughly 21-day development, a period when the embryo is forming key organs and tissues. This approach is often called embryonic thermal manipulation, and it is studied as a possible way to help chickens cope with heat later in life.
After hatching, the chicks were split again. Some received a regular feed and others received the same feed with a synbiotic added at 1 gram per kilogram of feed. A synbiotic combines probiotics, which are beneficial live microbes, with prebiotics, which are fibers that feed those microbes. The birds were raised until 42 days old, which is the usual market age for meat chickens.
Between days 21 and 28, all birds caught leucocytozoonosis, a blood parasite infection that spread during the trial. Every bird received the same antiparasitic treatment. Because all groups faced the same infection, the researchers could compare how the treatments held up under a real disease challenge.
Comparing the two incubation temperatures and the two feeding approaches together is important because the study tests whether one factor changes the effect of the other. Simply testing a feed supplement on chicks from normal eggs would miss this. Using the same disease challenge for every group also makes the comparisons fairer, since the infection affects all groups in the same way. Because the eggs were randomly assigned to temperatures and the chicks were split into feed groups, the study design can help separate the effect of each factor.
The study was published in a peer-reviewed poultry science journal, which means outside experts reviewed it before publication. The sample of 840 eggs is reasonably large for this type of trial. Groups were compared under identical conditions, including the same disease outbreak and treatment. However, the study was done in one location with one chicken breed, and some measured outcomes, such as gait and caecal bacteria, showed no clear differences. Readers should treat the findings as useful early evidence, not as settled practice.
What the Results Show
The clearest result was on hatching. Eggs warmed during incubation hatched at 87.7%, compared with 95.7% for eggs kept at the standard temperature. Warmed chicks also ate less starter feed and weighed less early on. By the end of the 42-day study, however, their final body weight was similar to the other birds. This suggests that early setbacks may not always carry through to market weight.
The feed supplement had a mixed effect that depended on incubation temperature. In chicks from normally incubated eggs, the synbiotic increased body weight gain and the height of the small villi in the upper intestine. Villi are tiny projections that help the gut absorb nutrients, so taller villi generally suggest better nutrient absorption. Across all birds, the supplement also improved feed conversion ratio, which measures how much feed is needed to produce each kilogram of weight gain.
In chicks from warmed eggs, the picture changed. The synbiotic increased phosphorus content in the tibia, the main shin bone, which suggests stronger bone mineralization. At the same time, it reduced villus height in the gut. The researchers described this as a shift in benefit: the supplement helped bones more and the gut less when the embryo had experienced warmer incubation.
Some outcomes did not change with either treatment. Gait score, which measures how smoothly birds walk, and latency-to-lie, which measures how quickly birds settle down to rest, were not affected. The bacterial makeup of the caecum, a pouch at the end of the small intestine, also showed no clear differences. These null results are useful because they show that the treatments did not alter every aspect of bird health.
A less welcome finding was that footpad dermatitis and hock burn scores increased only in birds that received the synbiotic and were incubated at the standard temperature. These are painful skin problems on the feet and lower leg that are linked to wet litter and poor welfare. The researchers did not identify a clear cause, so this result needs follow-up before drawing conclusions about the supplement’s welfare effects.
Earlier poultry research has shown that warming eggs during incubation can prepare chickens to tolerate heat later, but it can also reduce hatching success, which matches this study’s findings. Research on synbiotics and probiotics in chickens has often reported better growth and gut function, particularly in birds under stress or infection. This study adds an important layer by showing that the benefits of a feed supplement may depend on what happened before hatching. Because the field is still developing, more trials across different climates and breeds are needed to see whether these patterns hold.
The study examined one chicken breed in a tropical setting, so results may differ in other climates or with other breeds. Only one incubation temperature and one supplement dose were tested. The disease outbreak was not planned, though all groups were treated the same way. Some measurements were taken only at certain ages, which may miss short-term effects. Finally, this was research on animals, so it does not directly show how these findings would apply to human nutrition or health.
The Bottom Line
Research suggests that incubation conditions should be considered when planning feed programs for broilers. The strongest evidence supports the finding that warming eggs during incubation lowered hatchability in this study, which is a moderate-confidence result based on a single trial. The synbiotic’s benefits on growth and gut structure appeared mainly in birds from normally incubated eggs, which is a tentative finding that needs confirmation. Producers should test these approaches on their own farms before making major changes.
Poultry farmers, hatchery managers, and animal nutrition professionals should pay the most attention to these findings. Consumers who simply want to understand chicken production may find the results interesting but do not need to change their own habits. People who keep backyard chickens may also find the general lesson about incubation useful, though this study was done on commercial broilers in a specific setting.
In this study, differences in hatching and early feed intake were visible within the first weeks. Differences in gut structure and bone mineral content appeared later, around the middle and end of the 42-day growing period. Any farm applying these ideas would need to run its own trials over one full production cycle to see whether benefits appear under local conditions.
Frequently Asked Questions
Does warming chicken eggs during incubation affect how many chicks hatch?
Warming eggs to 38.5°C during days 8 to 14 of incubation lowered hatchability in a 2026 study. Hatch rates fell from 95.7% in standard-temperature eggs to 87.7% in warmed eggs, and the warmed chicks also ate less feed early on.
What is a synbiotic in chicken feed?
A synbiotic combines probiotics, which are beneficial live microbes, with prebiotics, which are fibers that feed those microbes. In a 2026 study, researchers added one gram per kilogram of feed to broiler diets to see how it affected growth and gut health.
Does a feed supplement help broiler chickens grow faster?
In a 2026 study, a synbiotic increased weight gain in chickens from normally incubated eggs and improved overall feed conversion. Its effects depended on incubation temperature, so benefits may not appear on every farm or in every flock.
Can egg incubation temperature change how strong chicken bones are?
A 2026 study found that chicks from warmed eggs had higher phosphorus content in their tibia bone when given a synbiotic. Phosphorus helps bones harden, suggesting that incubation conditions can change how feed additives affect bone development in broilers.
Want to Apply This Research?
- Log each batch’s hatchability rate, starter feed intake in grams per bird for days 1 to 21, and body weight at days 21, 28, and 42. Record the feed conversion ratio for each batch. Note the incubation temperature and whether a synbiotic was used, so you can compare outcomes across batches.
- Work with your hatchery to record incubation temperatures and ask whether any embryonic temperature changes were made. Before adding a synbiotic to feed, compare the hatch records and early feed intake of your flock with those of previous batches. Consider running a small side-by-side trial on one house before changing the whole operation.
- Track hatchability, weight gain, feed conversion, and footpad or hock health scores across several production cycles. Review the data every quarter to spot trends that a single batch might hide. Pay attention to welfare scores so that any benefit to growth does not come with a hidden cost to animal comfort.
This article summarizes a study of commercial meat chickens (broilers) raised under tropical conditions. The findings apply to animal farming and do not provide medical or dietary advice for people. Results from one trial may not apply to every farm, breed, or climate. Farmers should consult qualified poultry veterinarians or nutritionists before changing incubation practices or feed programs.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.