Dietary fiber is utilized by ruminal microorganisms as an energy source (Hall & Mertens, 2023) and plays a fundamental role in maintaining gastrointestinal health. Beyond its nutritional contribution, fiber provides the physical stimulation required for proper rumen function by promoting chewing activity and saliva secretion (Schmitz-Esser, 2021); (Zhang et al., 2025). The type and level of fiber used in production systems must consider feed cost and availability, as well as their effects on digestive physiology and animal performance, because diets with high fiber content or a predominance of long fiber particles may limit nutrient intake in sheep (Faryabi et al., 2023).

Numerous studies have demonstrated that feed processing, particularly grain processing, can reduce anti-nutritional factors and decrease the resistance of grains to ruminal fermentation (Risyahadi et al., 2023). (Zhong et al., 2018)reported increased feed intake, improved growth performance, modulation of ruminal fermentation, enhanced gastrointestinal development, and beneficial effects on cholesterol metabolism and animal health in sheep fed pelleted forage-based diets compared with those fed non-pelleted diets.

Nevertheless, additional processing strategies associated with pelleting may further enhance these effects and optimize dietary fiber utilization. Extrusion is widely used to increase the exposure of starch granules in grains to ruminal fermentation and digestion(Risyahadi et al., 2023) by subjecting feed ingredients to high pressure, moisture, and temperature.

However, limited information is available regarding the application of extrusion in high-forage diets for small ruminants, particularly those based on tropical forages, which are characterized by greater fiber complexity and stronger physical limitations to feed intake and digestion. In addition, previous studies evaluating processed diets in sheep have primarily focused on growing or feedlot animals (Zhong et al., 2018). Recent studies using extruded tropical forages in sheep diets have demonstrated promising effects on feed intake and digestibility (Silva et al., 2024). However, information remains scarce, especially in systems with high forage inclusion levels. The thermal and mechanical effects of extrusion may represent a viable strategy to alter the structural organization of fibrous feed components (Brand et al., 2023); (Ghorbani et al., 2020); (Gjorgjievski et al., 2022), thereby enhancing fiber intake, microbial colonization, and ruminal digestion and potentially improving nutrient utilization in high-fiber diets.

Therefore, the present study addresses an important gap in the literature by evaluating extruded diets (DExt) containing high levels of tropical forage (Urochloa grass) in adult ewes under high-forage feeding systems (up to 70% forage inclusion) as a strategy to improve fiber utilization. This study evaluated the effects of DExt containing Urochloa grass on dry matter intake (DMI), dry matter digestibility (DMD), ingestive behavior, and serum metabolites compared with a non-extruded corn silage diet. It was hypothesized that extrusion would allow greater forage inclusion without impairing feed intake, digestibility, or metabolic status in adult ewes.

Extruded diets (DExt) increased BW, DMI (DMI, DMI%BW, and DMI0.75), water intake from the drinker, and fecal score of ewes compared with corn silage-based diets (p<0.05) (Table 2). The DMI of animals fed corn silage represented only 42% of that observed in animals fed DExt. Both DMI (p = 0.02) and BW (p = 0.04) showed a quadratic response to increasing forage inclusion levels in DExt, with maximum values estimated at 65.0% forage inclusion. Water intake from the diet and total water intake (drinker + diet) were greater in animals fed corn silage (p<0.01). DMD was not affected by forage source or forage inclusion level (p>0.05) (Table 2).

ET, RT, TCT, and the number of ruminal movements were greater in animals fed corn silage than in those fed DExt, whereas IT, CE, and RE were greater in animals fed DExt, likely due to the higher DMI observed in these diets (p<0.04) (Table 3).

In addition, RT and TCT showed a quadratic response to increasing forage inclusion levels in DExt, with maximum values estimated at 65.0% forage inclusion (p<0.05). Conversely, IT exhibited an opposite quadratic response, decreasing up to 65.0% forage inclusion and increasing thereafter at 70.0% forage inclusion. CE and RE also showed a quadratic response, with minimum values estimated at 65.0% forage inclusion in DExt.

Serum concentrations of cholesterol, triglycerides, total protein, albumin, and creatinine were not affected by forage source or forage inclusion level in DExt (p>0.05) (Table 4). However, DExt increased serum urea concentrations compared with corn silage (p<0.01). Within the DExt, increasing forage inclusion levels promoted a linear reduction in serum urea concentrations (p<0.01). The serum glucose concentration was not affected by the forage source (p = 0.48); however, it showed a quadratic response to forage inclusion levels in DExt (p = 0.01), with the highest concentration observed in the diet containing 60.0% forage (50.25 mg dL⁻¹).

Regarding the glycemic response curve, the DExt containing 70.0% forage induced a glucose peak at 14:00 h, corresponding to 6 hours after feeding. Corn silage reduced blood glucose concentrations compared with DExt throughout the day (p<0.05). However, the decline in blood glucose concentration occurred only at 20:00 h in animals fed corn silage, whereas the reduction was observed at 17:00 h in animals fed DExt containing 52.5%, 65.0%, and 70.0% forage (Figure 1).

The high proportion of long particles in the corn silage used in the present study likely stimulated particle selection during feed intake (Malik et al., 2021), whereas this behavior was minimized in the DExt because of the uniform pellet size. After ingestion, mastication of the pellets may have further accentuated the differences in particle size between diets because Urochloa forage particles were reduced to 2 mm before extrusion. The increased intake of fine particles from DExt has been associated with reduced chewing activity and increased digesta passage rate (Findeisen et al., 2021), which may contribute to greater feed intake rates and increased DMI, as observed in the present study. This phenomenon occurs because smaller particles exit the rumen more rapidly, thereby reducing the physical limitations imposed by ruminal fill on the gastrointestinal tract (Dufreneix et al., 2019). Furthermore, (Malik et al., 2023) reported that pelleted diets reduce the rumen-filling effect because of their smaller particle size and compact physical form, which supports the greater DMI observed in animals fed DExt in the present study.

Conversely, the ingestion of larger fiber particles promotes ruminal fill, increases digesta retention time, and enhances masticatory activity for the mechanical breakdown of feed particles (Singer et al., 2024), as observed in the silage-based diets, which showed increased RT, TCT, and ruminal movements. This physical distension promoted by the long fiber particles likely acted as the primary limiting factor for ingestive capacity, explaining the lower DMI observed in silage-fed ewes. Despite the lower DMI, ewes fed corn silage exhibited greater total water intake. This finding is a direct consequence of the substantial difference in DM content between diets (approximately 31% vs. 91% DM for corn silage and DExt, respectively). The high moisture content of corn silage supplied a considerable amount of water through the feed, thereby offsetting the lower voluntary water intake from the drinker. In this context, dietary moisture content is a key factor influencing feed intake patterns and ingestive behavior, including water intake dynamics (Havekes et al., 2020).

Diets with higher DM content improved FE and intake dynamics, as evidenced by the greater FE and RE observed in DExt, while also increasing IT and nutrient flow available for BW gain (Wondater & Ayanie, 2023), corroborating the BW responses observed in the study. The ET pattern observed herein is consistent with the findings of (Li et al., 2021), who reported a greater feeding frequency associated with increased DMI in lambs fed pelleted diets.

Although DExt presented a similar particle size distribution, intake responses were more closely associated with forage inclusion level than with particle size per se. High forage inclusion increases neutral detergent fiber concentration and promotes rumen fill, which may limit feed intake, as observed in diets containing 70.0% forage (Faryabi et al., 2023). Conversely, the progressive increase in DMI observed in DExt up to 65.0% forage inclusion and 53.59% neutral detergent fiber likely allowed greater fiber intake by the animals, resulting in increased RT (Zhang et al., 2025) and reduced CE and RE, since diets with lower forage inclusion required less time spent ruminating.

However, despite the lower IT and FE observed in diets containing 65.0% forage, these diets increased BW compared with the other DExt, likely due to the greater nutrient supply promoted by the higher DMI. This response is consistent with the findings of (Oliveira et al., 2025), who reported that the physical structure of extruded pellets modulates chewing dynamics and RE in lambs.

The increase in DMI observed in animals fed DExt was accompanied by greater water intake from the drinker, reflecting the well-established relationship between feed intake and water consumption (Akinmoladun et al., 2019); (Silva et al., 2024). By contrast, corn silage diets supplied a substantial amount of water through the feed because of their high moisture content, which explains the lower voluntary water intake from the drinker. In the present study, the increase in water intake from the drinker observed in DExt occurred in response to the greater DMI. However, considering the approximately threefold higher water content of corn silage, total water intake was approximately 1.5 L day⁻¹ greater in ewes fed corn silage. These findings confirm that the physical form and moisture content of the diet are major determinants of water intake partitioning between drinking water and feed-derived water(Golher et al., 2021).

Considering the water intake requirement of 2.78 L day⁻¹ per kg of DMI recommended by the National Research Council (Council, 2007), corn silage increased total water intake by approximately 57%, whereas DExt reduced total water intake by approximately 50% relative to (Council, 2007) recommendations.

Commonly, an increase in passage rate, which likely occurred in the DExt evaluated in the present study, negatively affects nutrient digestibility because of the reduced retention time of digesta in the gastrointestinal tract (Zhang et al., 2019); (Malik et al., 2023). On the other hand, thermal processing may enhance nutrient availability, particularly through protein denaturation and improved enzymatic digestion (Oliveira et al., 2020); (Risyahadi et al., 2023). Although increased DMD has been reported for DExt (Risyahadi et al., 2023), this effect was not observed in the present study, likely because the diets had similar protein concentrations and high forage inclusion levels, which may have limited the contribution of improved protein digestibility to overall DMD. Additionally, the longer fiber particles in corn silage may have increased ruminal retention time, contributing to the similar digestibility observed among diets. The similar fecal score values, which remained within the range indicative of normal gastrointestinal function (Dickson & Jolly, 2011), further support the absence of major differences in digestive efficiency among treatments.

The lower DMI observed in animals fed corn silage likely reduced dietary protein intake, resulting in lower ruminal protein degradation and ammonia production (Chen et al., 2021). This may explain the lower serum urea concentrations compared with ewes fed DExt and is consistent with the findings reported by (Zhong et al., 2018) for pelleted diets. The linear reduction in serum urea concentrations with increasing forage inclusion levels in DExt may be attributed to the lower protein concentration of diets with greater forage inclusion. In diets containing 70.0% forage, the lower dietary protein concentration combined with reduced DMI may have intensified the reduction in ruminal protein degradation and circulating urea concentrations. Nevertheless, the similarity in albumin, creatinine, and total protein concentrations indicates that protein metabolism was not impaired despite the reduction in protein turnover and urea metabolism.

Cholesterol and triglycerides are associated with short-chain fatty acid synthesis and the availability of energy substrates in the organism (Varanis et al., 2021). The diets evaluated in the present study had similar total digestible nutrient concentrations, suggesting that energy intake may have been more closely associated with differences in DMI. However, no evidence of energy deficiency was observed, as indicated by the similarity in energy-related metabolites among treatments, likely because of the use of adult ewes as the experimental model. All metabolites remained within the reference range for adult sheep (Varanis et al., 2021).

(Zhong et al., 2018) also reported no differences in serum cholesterol concentrations in lambs fed pelleted versus non-pelleted diets, although high-density lipoprotein increased and low-density lipoprotein decreased under pelleted diets. In the present study, plasma lipoproteins were not evaluated, which limits conclusions regarding potential improvements in animal health associated with extruded or pelleted diets, as suggested by (Zhong et al., 2018).

The glycemic profile may be associated with postprandial nutrient utilization because glucose metabolism in ruminants largely depends on hepatic gluconeogenesis from ruminal fermentation products rather than direct intestinal glucose absorption (Syperreck et al., 2023); (Varanis et al., 2021). The higher glucose concentration observed at 14:00 h in the DExt containing 70.0% forage may be related to differences in nutrient availability and digestibility associated with DExt. By contrast, the more stable glycemic pattern observed in ewes fed corn silage may reflect the slower degradation of structural carbohydrates in non-extruded forage sources. Furthermore, the reduction in blood glucose concentrations after 17:00 h may be associated with lower feed intake and reduced nutrient availability throughout the day, consistent with the ingestive behavior observed in animals fed silage-based diets.

The increase in feed intake, IT, FE, RE, and serum urea concentrations observed in ewes fed DExt may be attributed to the extrusion and pelletization processes, which reduce particle size and increase the surface area available for ruminal microbial activity, particularly compared with the long-particle corn silage used in this study. Furthermore, the greater feed intake, RT, and blood glucose concentrations observed in diets containing 60.0% to 65.0% forage under extrusion highlight the potential of this processing method to support higher DMI even in diets with elevated forage inclusion levels.

Fully DExt enabled greater forage inclusion without impairing feed intake, DMD, or metabolic status in adult ewes. Compared with corn silage, DExt increased DMI, water consumption, feed efficiency, and serum urea concentrations, while DMD remained unchanged. Forage inclusion levels between 60.0% and 65.0% promoted greater DMI and water intake, as well as improved RE and higher early morning blood glucose concentrations. These findings indicate that DExt can be used as an alternative strategy to increase forage utilization in ruminant diets, allowing greater inclusion of high-fiber ingredients while maintaining animal performance and metabolic stability, which may contribute to more flexible feeding systems.

We certify that there are no conflicts of interest involving any financial, personal, or other relationships with individuals or organizations related to the material discussed in this manuscript.

We certify that generative AI and/or AI-assisted technologies were not used in the writing of this manuscript, nor in the analysis, interpretation of data, or preparation of figures and tables.