Maintaining liver and intestinal health becomes increasingly important as laying hens move into the later stages of production. A new study suggests that dietary bile acids could play a role in both areas, altering hepatic fatty-acid composition while simultaneously influencing the cecal microbiota of older hens.
Researchers from Shandong Agricultural University and the Shandong Provincial Center for Quality and Safety of Animal Products evaluated different levels of bile-acid supplementation in 1,080 Hy-Line Brown hens at 76 weeks of age.
Among the doses tested, 300 mg/kg produced the most favorable overall response, combining changes in hepatic fatty-acid composition with increased microbial diversity and a different cecal microbial profile.
KEY FINDING
The researchers found that 300 mg/kg of dietary bile acids most effectively improved hepatic fatty-acid composition and cecal microbial diversity under the conditions of the 35-day experiment.
Why focus on late-laying hens?
Extending the productive life of laying hens brings nutritional and metabolic challenges that differ from those encountered earlier in the production cycle.
As egg production declines during the late laying phase, energy intake may exceed the amount required for maintenance and egg synthesis. This imbalance can favor excessive lipid deposition in the liver, potentially contributing to poorer hepatic function, reduced laying performance and increased mortality.
Aging is also associated with changes in hepatic metabolic capacity, hormonal regulation and the intestinal microbial community. This makes the interaction between the liver and gut particularly relevant when evaluating nutritional strategies for older hens.
THE LATE-LAYING CHALLENGE
Supporting older hens is not simply a question of maintaining egg production. Changes in lipid metabolism and gut microbial composition can occur simultaneously, making the gut–liver axis an increasingly interesting nutritional target.
Bile acids do more than help digest fat
Bile acids are synthesized from cholesterol in the liver and are best known for their role in emulsifying dietary lipids and supporting fat digestion and absorption.
However, their physiological functions extend considerably further.
Bile acids also act as metabolic signaling molecules and participate in a two-way relationship with the intestinal microbiota. Gut microorganisms can modify bile acids, while bile acids themselves can influence microbial communities through antimicrobial activity and host signaling pathways.
This relationship means that dietary bile-acid supplementation could potentially influence hepatic lipid metabolism and intestinal microbial ecology at the same time.
Testing three supplementation levels
The researchers randomly assigned the 1,080 hens to four dietary treatments:
CON: basal diet with no supplemental bile acids
BA200: basal diet + 200 mg/kg bile acids
BA300: basal diet + 300 mg/kg bile acids
BA500: basal diet + 500 mg/kg bile acids
Each treatment contained six replicates of 45 hens. Following a seven-day acclimation period, the experimental diets were provided for 35 days.
The researchers then examined two principal areas: hepatic fatty-acid composition and cecal microbial communities.
Bile acids altered the liver fatty-acid profile
One of the clearest findings was a reduction in hepatic stearic acid (C18:0). Concentrations were significantly lower in all three bile-acid-supplemented groups compared with the control.
However, the response was not simply greater as the dietary dose increased.
The 300 mg/kg treatment stood out for several additional changes. Hens receiving this level showed significantly higher concentrations of oleic acid (C18:1n9c), total monounsaturated fatty acids (MUFAs) and n-3 polyunsaturated fatty acids (PUFAs).
The same group also showed a lower n-6/n-3 PUFA ratio.
The dose response matters: although all supplemented groups showed lower hepatic stearic acid, the most favorable overall fatty-acid profile was observed at 300 mg/kg rather than the highest 500 mg/kg dose.
Cecal microbial diversity also responded
The effects were not confined to the liver.
Microbiota sequencing showed that bile-acid supplementation altered the diversity and composition of the cecal microbial community.
The Chao1 index, which reflects microbial richness, increased significantly in all bile-acid groups. The Simpson diversity index was also significantly higher in the BA300 group.
These findings suggest that bile-acid supplementation influenced not only which microorganisms were present but also the overall structure of the cecal microbial ecosystem.
300 mg/kg AGAIN STOOD OUT
All three bile-acid treatments increased microbial richness according to the Chao1 index, while the 300 mg/kg treatment also increased the Simpson index, supporting the researchers’ conclusion that this dose produced the most favorable overall microbial response.
Changes extended to specific bacterial groups
Analysis of the bacterial communities revealed further differences between treatments.
LEfSe analysis indicated that the control group was characterized by a higher abundance of several opportunistic bacterial taxa, while supplementation shifted the microbial profile.
The authors highlighted the BA300 treatment in particular, reporting enrichment of Enterococcus and describing the overall microbial community at this supplementation level as more favorable and stable.
The results reinforce the idea that bile acids should not be viewed exclusively through the lens of fat digestion. Their interactions with microorganisms could form part of a broader gut–liver signaling network relevant to the metabolic health of aging hens.
More bile acids did not necessarily mean a better response
From a practical nutrition perspective, one of the most interesting aspects of the study is the apparent non-linear response to supplementation.
The researchers tested 200, 300 and 500 mg/kg, yet the intermediate dose consistently produced the most favorable combination of responses.
This is important because it suggests that the objective should not simply be to maximize bile-acid inclusion. Instead, dose optimization may be necessary to influence lipid metabolism and microbial ecology in the desired direction.
THE HIGHEST DOSE WAS NOT THE OPTIMUM
The 500 mg/kg treatment did not consistently outperform 300 mg/kg. Under the conditions of this experiment, the intermediate dose provided the strongest combined response across the hepatic fatty-acid and microbiota measurements.
A closer look at the gut–liver axis
The study is particularly relevant because previous poultry research has often examined the effects of bile acids on either lipid metabolism or intestinal health separately.
By evaluating hepatic fatty acids and cecal microbial composition simultaneously, the researchers sought to provide a more integrated picture of how nutritional bile acids might influence the gut–liver axis in aging laying hens.
This becomes increasingly relevant as the poultry sector seeks nutritional strategies capable of supporting hens through longer production cycles.
Improving metabolic resilience during late lay could potentially help producers maintain healthier birds as the physiological demands of aging, egg production and hepatic lipid metabolism converge.
What should producers take from the study?
The findings point to dietary bile acids as a potentially useful nutritional tool during the late laying phase, particularly because their effects may extend beyond conventional lipid digestion.
At 300 mg/kg, supplementation was associated with changes in hepatic fatty-acid composition, increased cecal microbial diversity and a microbial profile the researchers considered more favorable.
However, the findings should be interpreted within the scope of the experiment. The study evaluated one strain and age of laying hen under a specific feeding and management environment over 35 days. The microbiota analyses also describe associations and compositional changes; they do not by themselves establish that particular bacterial changes caused the observed hepatic responses.
Overall, the results suggest that carefully targeted bile-acid supplementation may offer a way to simultaneously influence liver lipid metabolism and the intestinal microbial ecosystem—two increasingly important areas when managing hens during extended laying cycles.
Source
Liu, Z., Jin, Y., Fan, Q., Zhang, Y., Fu, Y., Zhou, G., Jiang, S., Li, J., & Yang, W. (2026). Hepatic Fatty Acid Profile and Gut Microbiota Changes in Response to Dietary Bile Acid Supplementation in Late-Laying Hens. Poultry, 5(4), 58. https://doi.org/10.3390/poultry5040058