A special plant fiber called xylo-oligosaccharides (XOS) helps lambs grow heavier and digest food better, according to a 2026 study of 32 lambs published in Animal Bioscience. Lambs fed XOS-supplemented feed for 63 days gained more weight, ate more food daily, and digested plant fiber 22% more efficiently than lambs on regular feed. The supplement also increased beneficial digestive compounds in the lambs’ stomachs and shifted their gut bacteria toward more helpful types.
Researchers tested whether a special type of fiber called xylo-oligosaccharides (XOS) could help young lambs grow better. They gave one group of lambs regular feed and another group the same feed with added XOS for 63 days. The lambs that ate the XOS-supplemented feed grew heavier, ate more food, and had better digestion. According to Gram Research analysis, this affordable supplement appears to improve how lambs’ bodies break down plant material and changes the helpful bacteria in their stomachs in positive ways.
Key Statistics
A 2026 randomized controlled trial of 32 fattening Hu lambs found that dietary XOS supplementation increased final body weight and dry matter intake compared to control lambs over a 63-day period.
According to research reviewed by Gram Research, XOS supplementation increased neutral detergent fiber digestibility and the amount of digested plant fiber in lambs, improving nutrient extraction from feed.
A study of 32 lambs published in Animal Bioscience in 2026 showed that XOS supplementation increased total volatile fatty acid concentration and butyrate production in the rumen while decreasing isobutyrate and isovalerate.
Research on 32 fattening lambs demonstrated that XOS supplementation increased the relative abundance of Bacteroidetes bacteria while decreasing bacterial diversity indices, suggesting a shift toward a more beneficial gut community.
The Quick Take
- What they studied: Whether adding a special plant-based fiber called XOS to lamb feed would make them grow faster and digest food better
- Who participated: 32 young Hu lambs (a Chinese breed) that were about 3 months old and weighed around 20 kilograms at the start. Half got regular feed, and half got feed with XOS added
- Key finding: Lambs eating XOS-supplemented feed ended up heavier, ate more food overall, and digested plant fiber much better than lambs on regular feed after 63 days
- What it means for you: If you raise lambs or other livestock, adding this affordable supplement might help your animals grow bigger and healthier. However, this study only tested lambs, so results may differ for other animals
The Research Details
Scientists divided 32 young lambs into two equal groups. One group ate normal feed for 63 days, while the other group ate the same feed with 6 grams of XOS added per kilogram of dry feed. The researchers weighed the lambs on days 0, 21, 42, and 63 to track their growth. At the end, they collected stomach fluid samples from randomly chosen lambs to examine what was happening inside their digestive systems.
The researchers measured several important things: how much the lambs weighed at the end, how much food they ate each day, how much weight they gained daily, and how well their bodies broke down different nutrients. They also looked at the chemical compounds produced during digestion and identified which bacteria were living in the lambs’ stomachs using genetic testing.
This type of study is called a randomized controlled trial, which is considered one of the strongest ways to test whether something actually works. By randomly assigning lambs to each group, the researchers made sure the groups were similar at the start, so any differences at the end would likely be from the XOS supplement.
Understanding how supplements affect livestock growth and digestion helps farmers make better feeding decisions. This research is important because it shows how a natural plant-based fiber can improve animal health without using medications or artificial additives. The study also examined the actual bacteria living in the lambs’ stomachs, which helps explain why the supplement worked
This study had a reasonable number of animals (32 total), used a proper control group for comparison, and randomly assigned lambs to each group. The researchers measured multiple outcomes and used scientific methods to identify bacteria. However, the study only lasted 63 days and only tested one breed of lamb, so results might differ over longer periods or with different animals
What the Results Show
Lambs that received XOS supplementation weighed significantly more at the end of the 63-day study compared to lambs on regular feed. These lambs also ate more food each day on average. When researchers looked at weight gain over the entire study period, lambs eating XOS tended to gain weight faster, though the difference was not quite as dramatic as the final weight difference.
The most impressive finding involved digestion. Lambs eating XOS digested plant fiber (called NDF, or neutral detergent fiber) much more efficiently than control lambs. This means their bodies extracted more nutrition from the same amount of plant material. The amount of plant fiber they actually digested and used was noticeably higher in the XOS group.
Inside the lambs’ stomachs, the XOS supplement changed the chemical environment. The total amount of volatile fatty acids (VFAs), which are energy-producing compounds made during digestion, increased in XOS-fed lambs. Specifically, butyrate, a particularly beneficial VFA, was higher in the XOS group. Meanwhile, less desirable compounds called isobutyrate and isovalerate were lower.
The XOS supplement changed which bacteria lived in the lambs’ stomachs. The diversity of bacterial species decreased slightly, meaning fewer different types of bacteria were present, but the bacteria that remained were apparently more beneficial. Importantly, the total number of different bacterial species (measured by richness indices) stayed about the same. The supplement increased the relative abundance of Bacteroidetes, a major group of bacteria that helps break down plant material.
Previous research on prebiotics (supplements that feed beneficial bacteria) in livestock has shown mixed results. This study adds to growing evidence that XOS specifically may be a practical tool for improving lamb growth and digestion. The findings align with other research showing that plant-based fibers can shift bacterial communities toward more beneficial compositions. However, most previous studies on XOS in lambs have been limited, making this research a valuable addition to the field
This study only tested one breed of lamb (Hu lambs) over a relatively short period (63 days), so results might differ for other breeds or over longer feeding periods. The study used only 32 lambs total, which is a modest number. The researchers only collected stomach samples at the very end of the study, so they could not track how the bacterial community changed over time. Additionally, the study did not measure whether the improved growth translated to better meat quality or other practical outcomes that farmers care about
The Bottom Line
Based on this research, adding XOS supplement to lamb feed appears to be a safe and effective way to improve growth and digestion. The evidence is moderately strong for this specific breed and age group. Farmers considering this supplement should start with small amounts and monitor their lambs’ health and growth. This approach works best as part of an overall good feeding program, not as a replacement for quality feed
Lamb farmers and livestock producers should pay attention to these findings, especially those raising Hu lambs or similar breeds. Veterinarians and animal nutritionists may want to consider recommending XOS as part of feeding programs. Pet owners with goats or sheep might also find this relevant. However, this study only tested lambs, so results may not apply to other animals without additional research
Based on this study, you would expect to see noticeable differences in lamb growth within 3 to 4 weeks of starting XOS supplementation. The digestive improvements appeared throughout the 63-day period. For best results, the supplement should be given consistently from the start of the fattening period
Frequently Asked Questions
Does XOS supplement actually help lambs grow faster and bigger?
Yes, a 2026 study of 32 lambs found that those receiving XOS supplementation ended up heavier and ate more food daily than control lambs over 63 days. Weight gain rates also tended to be higher throughout the study period.
How does XOS improve digestion in lambs?
XOS acts as a prebiotic, feeding beneficial bacteria in the lamb’s stomach. This increases helpful digestive compounds called volatile fatty acids and shifts the bacterial community toward more beneficial types that break down plant material more efficiently.
What is the right amount of XOS to give lambs?
This study used 6 grams of XOS per kilogram of dry feed and found positive results. This dosage increased growth, feed intake, and digestion without negative side effects in the lambs tested.
Will XOS work for all types of lambs and sheep?
This study only tested Hu lambs, a Chinese breed, over 63 days. Results may differ for other breeds, ages, or longer feeding periods. Farmers should monitor their specific animals to see if the supplement works for their operation.
Is XOS supplement safe for lambs?
Based on this research, XOS appears safe and well-tolerated in lambs. The supplement improved digestion and growth without causing negative health effects during the 63-day study period.
Want to Apply This Research?
- Track weekly lamb weight gain and daily feed intake. Record these measurements every 7 days and compare growth rates between supplemented and non-supplemented groups to see if the supplement is working for your specific lambs
- If using the app to manage a flock, add a reminder to mix XOS supplement into feed at the correct rate (6 grams per kilogram of dry feed) each time you prepare meals. Set alerts to weigh lambs weekly and log the results to monitor progress
- Create a long-term tracking system that records weekly weights, daily feed consumption, and visual health observations over the entire fattening period. Compare these metrics between lambs receiving XOS and those on regular feed to determine if the supplement provides value for your operation
This research describes results from a controlled study of young lambs over 63 days. Individual results may vary based on breed, age, overall diet quality, and management practices. Before adding any supplement to your livestock feed program, consult with a veterinarian or animal nutritionist familiar with your specific animals and operation. This study does not constitute medical or veterinary advice. The findings apply specifically to fattening Hu lambs and may not apply to other species or breeds without additional research.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.