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20 May 2026

How starch structure & protein reduction shape gut health in weaned pigs

Diana Luise

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Synchronizing nutrition: how starch structure and protein reduction shape gut health and growth in weaned pigs

Introduction: rethinking protein and carbohydrates in piglet nutrition

In recent years, animal nutrition research has increasingly focused on reducing crude protein (CP) in diets, driven by both environmental and health considerations. Lower-protein diets can reduce nitrogen excretion and mitigate gut disorders, but they often come with a trade-off: reduced growth performance, especially in young animals such as weaned pigs, which are characterized by a high amino acid (AA) requirement.

A key challenge for low CP diets integrated with synthetic AAs lies in nutrient synchronization. When diets are supplemented with free AAs to compensate for reduced protein, these are absorbed rapidly into the bloodstream. However, glucose, derived mainly from starch digestion, is released more slowly.

This mismatch between amino acid absorption and glucose availability can limit protein synthesis efficiency, leading to amino acid catabolism rather than growth.

One promising strategy to address this issue involves modifying the amylose-to-amylopectin (AM/AP) ratio in dietary starch. Amylopectin, a highly branched molecule, is digested more rapidly than amylose, resulting in faster glucose release.

Therefore, reducing the AM/AP ratio may help synchronize glucose and AAs availability, potentially improving metabolic efficiency.

Reducing the amylose-to-amylopectin ratio can accelerate glucose release and improve synchronization with amino acid absorption.

Two recent studies explored this concept in weaned and nursery pigs, investigating how low-protein diets combined with altered starch structure influence growth, gut health, microbiota, and metabolism.

Study designs: two approaches to the same nutritional challenge

Study 1: Early post-weaning phase under experimental conditions (Correa et al., 2024)

The first study evaluated the effects of reducing both CP and the AM/AP ratio in newly weaned pigs under controlled experimental conditions. Piglets were fed three different diets:

CTR: standard CP and moderate amylopectin content
LP: low CP with standard AM/AP ratio
LPLA: low CP with low AM/AP ratio

To reduce the AM/AP ratio, conventional corn was replaced with waxy corn containing approximately 98% amylopectin.

Across all diets, standardized ileal digestible lysine levels were maintained similarly among treatments, allowing researchers to isolate the effects of protein level and starch structure.

Study 2: Extended nursery phase under commercial farm conditions (Lee et al., 2026)

The second study investigated a more applied feeding strategy under commercial farm conditions using 540 post-weaned piglets over a longer nursery period.

Similarly to Study 1, lysine and other essential AAs were carefully balanced across diets, ensuring that performance differences were not due to essential amino acid deficiencies but rather to protein level and starch digestion dynamics.

From experimental conditions to real-world application

A key aspect when interpreting these findings is the difference in experimental context between the two studies.

In Study 1, pigs were raised under controlled experimental conditions, and diets included a relatively high proportion of processed starch sources. These ingredients are known to enhance starch digestibility and accelerate glucose release.

In contrast, Study 2 was conducted under commercial farm conditions, where animals were exposed to more variable environmental and management factors.

The second study demonstrated that reducing the AM/AP ratio can be effective even under practical commercial production conditions.

Growth performance: benefits and limitations

Both studies confirmed a key limitation of low CP diets:

In Study 1, pigs fed low-protein diets showed lower body weight and average daily gain.
Piglets fed the LPLA diet maintained body weight comparable to controls during the first four weeks post-weaning.
In Study 2, both LP and LPLA groups had lower body weight and growth rates compared to controls during later stages.
However, the lower AM/AP ratio improved feed efficiency during later nursery phases.

Reducing the AM/AP ratio does not completely restore growth performance but may partially compensate for metabolic inefficiencies associated with low-protein diets.

Gut health and diarrhoea: early benefits of dietary modulation

One of the most consistent findings across both studies concerns improvements in gut health:

Pigs fed the low AM/AP diet showed significantly lower diarrhoea incidence during the first week post-weaning.
Low-protein diets increased faecal dry matter during early stages.
These changes suggest better water absorption and reduced diarrhoea severity.

Early post-weaning gut health improved when low-protein diets were combined with lower AM/AP ratios.

Microbiota: diversity and functional modulation

Both studies explored how diet shapes the gut microbiota:

In Study 1, the LPLA diet increased alpha diversity, indicating a more resilient microbial ecosystem.
In Study 2, the LPLA diet influenced beta diversity and specific bacterial taxa over time.

Together, these findings suggest a transition from early diversity enhancement to later functional microbiota modulation.

The low AM/AP strategy influenced both microbial diversity and microbial metabolic activity in nursery pigs.

Metabolomic data from Study 2 also showed reduced faecal abundance of amino acids and lower lactate and uracil concentrations in pigs fed the LPLA diet. These changes suggest reduced protein fermentation in the large intestine and potentially lower harmful microbial activity.

Conclusion: toward smarter, scalable nutrition

These studies highlight a key principle of modern nutrition: nutrient timing and structure matter. Reducing crude protein remains a promising strategy for sustainability and gut health, but its success depends on optimizing nutrient utilization.

Adjusting the AM/AP ratio offers a novel way to improve metabolic synchronization. Importantly, evidence from both controlled and commercial settings suggests that this approach is not only biologically sound but also practically applicable and economically promising.

Future precision nutrition strategies may increasingly combine protein reduction, amino acid balancing, and starch structure optimization to improve gut health, feed efficiency, and sustainability in swine production.

References

Correa, F., Luise, D., Virdis, S., Negrini, C., Polimeni, B., Amarie, R. E., Serra, A., Biagi, G., & Trevisi, P. (2024). Reduction of amylose–amylopectin ratio in low-protein diets: Impacts on growth performance and intestinal health in weaned pigs. Journal of Animal Science, 102, skae370.

Lee, J., Correa, F., Laghi, L., Bencivenni, S., Bigi, D., Biagi, G., Palumbo, F., Trevisi, P., & Luise, D. (2026). A novel low-protein diet feeding strategy with reduced amylose/amylopectin ratio: Effects on growth performance, gut health, and behaviour in nursery pigs. Veterinary and Animal Science, 32, 100631.

Acknowledgements

The authors acknowledged Pioneer Hi-Bred Italia SRL for supplying the waxy maize and recognized funding support from the MELioR DIET project, the SustainableHeavySuis Project, the Emilia Romagna Region, Agritech National Research Center, and the European Union Next-GenerationEU initiative.