Gram Research analysis of a 2026 study found that feeding growing gilts diets with up to 50% soybean hulls slowed their growth and delayed puberty without reducing litter size. Across 4,346 gilts, first-parity pigs born averaged 14.8 per sow, compared with 15.0 on the standard diet, a difference the researchers did not consider significant.
Gram Research analysis of a 2026 study in Translational Animal Science found that adding soybean hulls, a high-fiber leftover from soybean processing, to the diets of young female pigs slowed their growth without reducing the number of piglets they later produced. The researchers followed 4,346 gilts, which are young female pigs raised for breeding, across 10 rooms on a commercial farm. Pigs given increasing amounts of hulls, up to half of their diet, grew more slowly, carried less back fat, and reached puberty later. Once these gilts became mothers, their first litters were about the same size as those of pigs fed a standard corn and soybean meal diet. The researchers suggest the approach could help farmers manage how fast breeding animals grow while protecting productivity. Because the study was conducted in pigs, it does not directly apply to human diets.
Key Statistics
A 2026 study of 4,346 gilts published in Translational Animal Science found that diets containing up to 50% soybean hulls slowed growth without meaningfully changing the number of piglets born in the first litter.
In that study, gilts fed a standard corn and soybean meal diet weighed an average of 102.2 kilograms, compared with 94.8 kilograms in gilts fed increasing levels of soybean hulls.
First-parity sows averaged 13.0 weaned pigs per litter on the control diet and 12.9 on the soybean hull diet, showing little to no difference in productivity.
The Quick Take
- What they studied: Researchers asked whether feeding young female pigs more soybean hulls, a high-fiber ingredient, would slow their growth and improve how they perform once they have their first litter.
- Who participated: The study included 4,346 gilts, which are young female pigs raised for breeding. They came from 10 rooms on a commercial farm and were weaned at about 21 days old. Smaller groups of these pigs were also checked for hormone levels, body fat, and signs of puberty.
- Key finding: Pigs fed soybean hulls grew more slowly, had less back fat, and reached puberty later. Their first litters were similar in size: 14.8 piglets born per sow compared with 15.0 on the standard diet, a difference the researchers did not consider statistically significant.
- What it means for you: If you raise or work with breeding pigs, this research suggests soybean hulls may be a useful tool for managing growth rate without lowering litter size. Results are specific to pigs and to the diets tested, so farmers should work with a nutritionist before making feed changes.
The Research Details
The researchers divided young female pigs into two feeding groups after they were weaned from their mothers at about 21 days of age. One group received a control diet based mainly on corn and soybean meal, which is the standard approach. The other group, called the slow growth group, received diets that contained increasing amounts of soybean hulls, reaching up to 50% of the diet, beginning when the pigs weighed about 25 kilograms.
The study tracked the animals for their whole first breeding cycle, measuring growth, signs of puberty, and reproductive results. Smaller subsets of pigs were examined more closely. About 150 pigs per group were checked for vulva development, which is a common sign of readiness to breed. About 40 pigs per group had blood drawn to measure reproductive hormones, and ultrasound scans estimated back fat and muscle depth. Each farm room was treated as one unit in the analysis, which helps account for differences between groups of animals housed together.
Because the work took place on a working commercial farm with thousands of animals, the results reflect real production conditions rather than a small controlled laboratory setting.
Comparing two feeding groups at the same time is a strong way to test cause and effect. Random assignment and a control group help show whether the difference came from the soybean hulls or from something else. Tracking animals through their first breeding cycle matters because farmers care about long-term results, not just early growth. Measuring hormones and body composition helps explain how the diet changed development, not only how much pigs weighed.
The large number of animals, the use of several rooms, and the real-farm setting are strengths. The analysis was based on cohorts, or groups of animals that started together, which is an appropriate way to handle animals housed in shared rooms. However, the published summary is brief and some statistical details are not fully clear, so readers should look at the full paper for exact values. Findings also come from one breeding line and one company’s management system, so results may vary elsewhere. Readers should also keep in mind that the study measured productivity only through the first litter.
What the Results Show
Gilts fed the control diet were heavier than those on the soybean hull diet, averaging 102.2 kilograms compared with 94.8 kilograms. The difference shows that adding hulls, which dilute the energy in feed, slowed how quickly the pigs gained weight. This was the main goal of the study, and the results suggest the approach works as intended.
The hull diets also reduced back fat, which is the layer of fat under the skin measured by ultrasound. Lower back fat is linked to slower overall growth and can be a useful target when managing breeding animals. The researchers also reported that puberty began later in the hull-fed group, which could shift the timing of when these gilts are first bred.
The most important result for farmers was that reproduction held steady. The number of piglets born in the first litter was 15.0 per sow in the control group and 14.8 in the soybean hull group. The number of piglets weaned, meaning those that survived to weaning, was 13.0 compared with 12.9. Neither difference was large enough to be considered a real change in performance.
Together, these findings suggest the diet can slow growth in a controlled way while keeping litter size close to standard levels. Because the study measured only the first parity, the long-term effects on later litters remain unknown.
Researchers also looked at vulva development, hormone levels, and body composition in smaller groups of pigs. These measures help explain the timing of puberty and the physical changes that happen as gilts mature. Delayed puberty can be useful for managing when breeding starts, but it can also affect how old an animal is at first breeding, so the overall timeline matters for farm planning. These secondary measures support the main finding that the diet changes development without hurting reproductive output.
Previous research on fiber in pig diets has shown that high-fiber ingredients can reduce energy intake and slow growth in growing animals, which is consistent with what this study found. This research extends that idea to breeding gilts and tracks outcomes through their first litter, which is more relevant to farm productivity than growth alone. Earlier work on feed restriction in breeding pigs has often focused on body condition, so this study adds evidence that a fiber-based approach can be an alternative.
The study focused on one breeding line and one management system, so results may not apply to all farms or genetic lines. Only the first litter was measured, so it is not clear whether the effects continue across later breeding cycles. The summary provided does not include every statistical detail, so readers should consult the full paper for exact comparisons. Some subgroups were small, which makes detailed hormone and body composition results less certain than the main growth and litter size findings. The study also did not report on costs, feed efficiency in dollar terms, or animal welfare outcomes in depth.
The Bottom Line
Based on this study, soybean hulls appear to be a practical option for slowing growth in breeding gilts without reducing first-litter size. Confidence is moderate because the study was large and well-designed but measured only one reproductive cycle on a limited set of farms. Producers should test the approach on a small scale, monitor body condition and breeding timing, and consult a swine nutritionist before making changes to a full herd.
Swine producers, farm managers, nutritionists, and herd veterinarians who work with breeding gilts should pay attention to these findings. Students and researchers in animal nutrition may also find the results useful. People who are not involved in pig production, including most consumers, do not need to change anything based on this study. Soybean hulls are not a human dietary recommendation.
In this study, changes in growth and back fat were measured during the gilt development period, which lasted until breeding and the first litter. Farmers who adopt this approach can expect to see differences in growth rate within the feeding period and changes in puberty timing before breeding. Long-term effects on later litters are not yet known and would require further research.
Frequently Asked Questions
Can soybean hulls slow down growth in breeding gilts?
Research shows that feeding increasing levels of soybean hulls, up to 50% of the diet, slowed growth and reduced back fat in gilts beginning at about 25 kilograms. The gilts also reached puberty later, according to a 2026 study of 4,346 animals.
Do soybean hulls affect how many piglets a sow has in her first litter?
In a 2026 study of 4,346 gilts, sows fed soybean hulls averaged 14.8 piglets born compared with 15.0 on standard diets. Weaned numbers were 12.9 versus 13.0, and researchers found no meaningful effect on first-litter productivity.
What are soybean hulls used for in animal feed?
Soybean hulls are the fibrous outer coating of soybeans that remains after oil and protein are processed. They are high in fiber and low in energy, so adding them to feed dilutes calories and can slow animal growth when used at controlled levels.
Does this soybean hull research apply to human diets?
This study was conducted in young female pigs, so its findings do not apply directly to people. It is most relevant to pig producers who manage breeding animal growth. People interested in dietary fiber should consult human nutrition research and a healthcare provider.
Want to Apply This Research?
- Record each gilt’s weight every two weeks from weaning through breeding, and note the date of first heat and the date of first breeding. Also track the daily amount of feed and the percentage of soybean hulls in the diet. Compare these numbers against the control group to see whether growth targets are being met.
- Use the app to set a target weight range for gilts based on your herd plan, then log weekly weights and adjust the hull percentage in the feed with your nutritionist’s guidance. Flag any gilt that falls well below or above the target so you can review her feed and health records.
- Maintain a long-term record for each breeding cycle, including age at first breeding, number of piglets born, number weaned, and body condition scores. Compare results across herd groups each season and review them with your veterinarian and nutritionist to confirm that growth control is not affecting later litters.
This article summarizes a research study on young female pigs raised for breeding and is intended for general information only. The findings do not apply directly to human diets or health. Pig producers should consult a qualified swine nutritionist or veterinarian before changing feed programs, and readers should review the full published paper for complete data.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.