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Effect of Fermented Broken Rice on Growth Performance and Rumen Fermentation Parameters of Hu Lambs

Q
Q..J. Wu1
Z
Z.B. Zhao1
R
R.K. Zhang1
J
J.X. Yang1
Y
Y.X. Li1
Y
Y. Ma1
Y
Y.Q. Wang1,*
1College of Animal Science and Technology, Henan University of Science and Technology, Luoyang 471023, Henan, PR China.

ABSTRACT

Background: The experiment was to investigate the effects of fermented broken rice (FBR) supplementation on growth performance, nutrient digestion and metabolism, and rumen fermentation in Hu lambs.

Methods: A total of 120 weaned Hu lambs were randomly allocated to 4 treatment groups with three replicates per group: a control group fed a basal diet, and three treatment groups supplemented with 10, 20 and 30 g/d FBR per lamb, respectively. The feeding trial lasted 60 days.

Result: The results showed as follows: compared with the Con group, FBR supplementation increased the average daily gain (ADG) and average daily feed intake (ADFI) of lambs from day16 to 45 (p<0.05), while no differences in ADFI were observed from day 46 to 60. FBR supplementation also markedly improved the apparent digestibility of organic matter, crude protein and neutral detergent fiber, as well as apparent nitrogen digestibility and nitrogen deposition rate, the ruminal ammonia nitrogen, propionic acid and butyric acid contents (p<0.05). Meanwhile, FBR reduced gross energy metabolizability, ruminal acetic acid proportion, and acetate-to-propionate ratio (p<0.05). In conclusion, graded FBR supplementation improves the growth performance of Hu lambs by enhancing nutrient digestibility, regulating energy supply, and optimizing ruminal fermentation characteristics.

INTRODUCTION

Broken rice (BR) is a major by-product of rice milling, forming an abundant underexploited agricultural resource suitable for livestock feed. Distince from conventional cereal feeds, BR contains highly digestible starch, crude protein and fiber, alongside bioactive compounds including fatty acids, rice polyphenols, rice bran polysaccharides and γ-oryzanol (Che et al., 2012; Miyaji et al., 2014; Kotupan and Sommart, 2021). These nutrients and bioactive substances endow BR high digestibility and physiological functions, such as antioxidant, anti-inflammatory and immunomodulatory activities, making it an affordable alternative feed material for animal breeding (Nguyen et al., 2022, 2024).
       
Numerous studies have validated the feeding value of BR for monogastric and ruminant animals. Nutritional analysis shows BR contains 4.2 Mcal/kg digestible energy and 3.7 Mcal/kg metabolizable energy (Miyaji et al., 2012). Adding BR to diets raises total tract and ileal digestibility of gross energy, organic matter and crude fat in weaned pigs (Che et al., 2012). For dairy cows, replacing corn with BR increases ruminal propionate proportion and lowers the acetate-to-propionate ratio to optimize volatile fatty acid composition (Miyaji et al., 2012, 2014). In fattening beef cattle, BR improves rumen fermentation, promotes fatty acid synthesis, raises energy supply and enhances carcass quality (Kotupan and Sommart, 2021). Proper BR addition does not disrupt rumen activity or growth of Hanwoo steers, proving BR is safe and usable for ruminants (Yang et al., 2020).
       
Despite its nutritional merits, raw BR faces obstacles limiting wide ruminant application. Raw BR has weak structural stability and poor processing performance, coupled with low ruminal starch degradation rate. It also carries anti-nutritional substances such as non-starch polysaccharides, phytic acid, lectins and excess lipase, which reduce feed palatability and nutrient absorption and weaken its feeding value (Wu et al., 2015). Microbial fermentation addresses these drawbacks: it breaks down anti-nutrients, splits large nutrients into readily absorbable small molecules and accumulates functional metabolites, lifting the feeding value of agricultural by-products (Wang et al., 2020; Nguyen et al., 2024).Current BR research mainly focuses on direct feeding for pigs and poultry, while fermented rice by-products are mostly tested on cattle. Few systematic trials have evaluated fermented broken rice (FBR) for sheep production. How FBR regulates lamb growth, whole-body nutrient digestibility and nitrogen metabolism remains unclear, creating an obvious research gap in small ruminant nutrition. The present study hypothesized that dietary FBR supplementation could eliminate the adverse effects of anti-nutritional factors in raw BR, optimize ruminal nutrient digestion and nitrogen retention and improve growth performance of Hu lambs. Therefore, this study was conducted to investigate the effects of FBR on growth performance, nutrient digestibility, nitrogen retention in Hu lambs.
 
Highlights
 
1. Fermented broken rice (FBR) supplementation improved growth performance and feed intake of Hu weaned lambs.
2. FBR increased nutrient digestibility, nitrogen deposition and ruminal glucose, NH3-N, propionate and butyrate  concentrations in Hu sheep.
3. Dietary FBR reduced gross energy metabolizability, ruminal acetate content and acetate-to-propionate ratio and optimized rumen fermentation profile.

MATERIALS AND METHODS

Microbial strain culture and inoculum preparation
 
The strain used for broken rice fermentation was Lactobacillus acidophilus , purchased from the Central Kay Guangdong Microbial Technology Co., Ltd. (Guangzhou, Guangdong, P.R. China). The strain activation and culture procedures followed standard microbial fermentation protocols described by Wang et al. (2020) with minor modifications. Briefly, the freeze-dried Lactobacillus acidophilus strain was revived and streaked onto Sabouraud dextrose agar (Oxoid Ltd., UK), then statically incubated at 24°C for 7 d to obtain single colonies. Purified colonies were picked and transferred to liquid SDA medium for expanded culture.
       
A fuchs-Rosenthal hematocytometer was used to count viable bacteria in the inoculant suspension, standardized to 4.8 × 10 CFU/mL. Per unit fermentation substrate required 0.25 g of this bacterial suspension (Cao et al., 2011). Uniform inoculum concentration was applied to all fermentation batches to stabilize fermentation efficiency and eliminate batch differences.
 
Preparation, fermentation procedures and chemical characterization of fermented broken rice
 
Broken rice used in this experiment was derived from Yuanyang Rice, a local rice planted in Henan Province, China and freshly harvested in summer 2023. After natural air-drying at 26°C, raw BR was crushed and sieved through a 0.3 to 0.5 mm screens to remove rice husk and bran impurities, improving substrate uniformity and microbial contact during fermentation (Zhang et al., 2010).
       
Enzymatic saccharification was conducted before fermentation to boost nutrient availability. Food-grade acetic acid adjusted ground BR pH to 5.0; the substrate was heated to 40-50°C, mixed with commercial glucoamylase and held at 60°C to break down macromolecular starch into reducing sugars as carbon sources for microbial growth. Standardized L. acidophilus liquid inoculum was added at 1.5% (v/w). The solid fermentation medium ratio (w/w) was saccharified BR: potato: glucose: agar = 10:1.0:1.0:0.5, supplemented with nutritive salt solution (MgSO4 ·7H2O: (NH4)2SO4: glucose: KH2PO4 = 1:5:6:2). The mixture fermented for 36 h at 28~30°C under natural humidity; this duration was proven optimal for rice by-products to degrade anti-nutrients and accumulate beneficial metabolites in previous research.
       
FBR was freshly manufactured weekly with a 3000 kg vertical mixer for feeding trials. Each 1500 kg mixed fermentation batch was compacted, sealed in food-grade plastic drums and anaerobically ensiled outdoors at 26~35 °C for no less than 7 d. After ensiling, FBR was air-dried to 950 g/kg DM, ground and sieved through a 0.5 mm mesh for uniform dietary addition. Nutrient profiles of raw BR and FBR were tested before feeding, with compositional changes listed in Table 1. Fermentation lowered anti-nutrient levels and raised crude protein and digestible nutrient contents of BR.

Table 1: Nutrients and compounds in broken rice before and after fermentation.


 
Experiment location and animal care
 
The feeding trial ran from June to August 2023 at Kunyuan Agricultural Cooperative, Henan Province. All animal handling, feeding and sampling procedures obtained approval from the Institutional Animal Care and Use Committee of Henan University of Science and Technology (Approval No. IAUC-0586. 2023) and complied with national standards for laboratory animal welfare.
 
Lamb, management, experimental diets and experimental design
 
A total of 120 healthy 60-day-old male Hu lambs with similar initial body weight (19.38±0.98 kg) were randomly allocated to 4 dietary groups in a randomized complete block design. Each group was replicated 3 times with 10 sheep per replicate, fed as follows: (1) Control group (CON): basal TMR diet without FBR; (2) FBR 1 group: basal diet+ 10 g/ day /lamb FBR; (3) FBR 2 group: basal diet + 20 g/ day /lamb FBR; and (4) FBR 3 group: basal diet + 30 g/ day /lamb FBR. The entire experimental period lasted 60 d, including a 45-day formal trial collection period and a 15-day adaptation period. The basal TMR diet was formulated following China Agricultural Standard (NY/T 816-2004)  for mutton sheep feeding and the diet composition and nutrient levels are shown in Table 2.

Table 3: Effects of fermented broken rice on the growth performance of Hu lambs.


       
Lambs were housed in independent 4.0 m × 3.0 m pens with free access to feed and water, fed twice daily at 08: 00 and 17: 00. The lambs were fed diets with the same composition and the only difference was the addition of FBR. The FBR was mixed in the basal diet. Daily feed provision and residual feed were recorded at 08:00. Housing temperature maintained at 26°C with daily light duration below 10 h; feeding volume was adjusted according to lamb weight and leftover feed to achieve ad libitum intake.
 
Sample collection and processing
 
Lambs were weighed before feeding at 08:00 on days 0, 15, 30, 45 and 60 to calculate ADG. Daily feed supply and residuals were weighed to compute feed intake and F/G ratio. Total feces and urine were collected over days 50 ~ 54 to measure nutrient digestibility, energy metabolism and nitrogen balance. All feed and leftover samples were collected daily, weighed and frozen for 5 consecutive days.

Feces were fully gathered in stainless steel trays behind tie stalls with separate drainage for urine. Fecal residues were scraped from under lamb hind legs every 4 h and weighed; 50 g/kg of total fresh feces was oven-dried at 65 °C for 48 h, pooled and stored at -18°C. Urine was collected in 5 L plastic containers pre-loaded with 20 mL 50% (wt/wt) sulfuric acid solution, diluted, mixed, subsampled and frozen at -20°C for later analysis.
       
On day 60, two lambs per replicate were fasted for 12 h and transported to a local abattoir for slaughter. A rumen suction device collected 250 mL ruminal fluid 2 h post-feeding. Ruminal pH was measured immediately with a portable CG840 pH meter (Scho Geräte, Germany). Remaining fluid was centrifuged and preserved in liquid nitrogen for rumen fermentation parameter detection.
 
Biochemical analysis of samples
 
The contents of dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE) and total nitrogen (N) in feed, residual feed, feces and urine samples were determined using standard feed analytical procedures. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were measured with an ANKOM 200 Fiber Analyzer by standard fiber analysis protocols. Gross energy (GE) was determined using a PARR-6400 automatic oxygen bomb calorimeter. Ruminal ammonia nitrogen (NH3-N) concentration was determined via phenol-sodium hypochlorite colorimetry and volatile fatty acid (VFA) contents were quantified using a CP 9002 gas chromatograph (Chrompack, Middelburg, Germany).
 
Statistical analysis
 
All experimental data were sorted and preprocessed in Excel 2021. Qualified data were analyzed by one-way ANOVA and Duncan’s multiple range test was used for post-hoc multiple comparisons. All statistical analyses were performed using SPSS 26.0 software (SPSS Inc., Chicago, IL, USA). Data were presented as means ± standard error of the mean (SEM). Differences were considered statistically significant at P<0.05.

RESULTS AND DISCUSSION

Growth performance
 
The growth performance of Hu lambs supplemented with different levels of fermented broken rice (FBR) is presented in Table 3. No significant differences were observed in ADG, ADFI and F / G of Hu lambs among all groups in the periods of 0 to 15 d (p>0.05). From day 16 to 30, 31 to 45, 46 to 60 and 0 to 60, lambs receiving FBR had greater ADG and ADFI  and the lower F/G compared with the CON group (p<0.05). No significant differences were detected among the FBR1, FBR2 and FBR3 groups for all growth indices throughout the trial (p >0.05), indicating no obvious linear dose-response relationship within the three FBR addition levels.

Table 3: Effects of fermented broken rice on the growth performance of Hu lambs.


 
Apparent digestibility, energy andnitrogen metabolites of dietary nutrients
 
The effects of FBR supplementation on nutrient apparent digestibility in Hu lambs are summarized in Table 4. Compared with the CON group, FBR supplementation increased the OM, CP and NDF digestibility (p<0.05). The OM digestibility increased from 55.06% in the CON group to 61.84%~63.50% in FBR groups, CP digestibility increased from 60.83% to 67.95%~70.86% and NDF digestibility increased from 58.36% to 66.76%~67.33%. No significant differences were found in the apparent digestibility of DM, EE and ADF among all four groups (p>0.05). Consistent with growth performance results, no differences in nutrient digestibility were observed among the FBR groups (p>0.05) and digestibility did not rise further when FBR addition increased from 10 to 30 g/d.

Table 4: Effects of fermented broken rice on the nutrients apparent digestibility, energy and nitrogen metabolites of Hu lambs.


       
No differences were observed in GEI, FE, DE, ME, apparent GE digestibility and DE metabolizability among all groups (p>0.05). UE was higher in the FBR2 group than in other groups (p<0.05), while FBR1 and FBR3 showed no difference compared with the CON group (p>0.05). Notably, the metabolizability of gross energy was decreased in all FBR groups relative to the CON group (p<0.05). Similarly, no progressive dose-response changes were identified among FBR groups for all energy metabolism parameters, demonstrating that increasing FBR dosage did not induce linear alterations in lamb energy metabolism characteristics.
       
No differences in NI, TEN and DN were detected across all treatments (p>0.05). However, compared with the CON group, all FBR groups exhibited reduced FN and UN excretion (p<0.05), indicating that FBR supplementation reduced nitrogen loss. Furthermore, FBR supplementation improved nitrogen utilization efficiency: ND, ADN and nitrogen deposition rate were higher in FBR groups than in the CON group (p<0.05). No statistical differences were found among the FBRgroups, indicating that all tested FBR dosages effectively enhanced nitrogen retention without significant dose-dependent effects (p>0.05).
 
Ruminal fermentation parameters
 
Ruminal fermentation characteristics of Hu lambs were altered by dietary FBR supplementation (Table 5). Ruminal pH, total volatile fatty acid concentration, iso-butyric acid, valeric acid and iso-valeric acid contents remained unchanged among all treatments (p>0.05). Compared with the CON group, FBR supplementation increased NH3-N, propionic acid and butyric acid concentrations (p<0.05), while decreasing acetic acid proportion and the acetate-to-propionate ratio (p<0.05), which optimized ruminal fermentation pattern toward higher energy utilization efficiency.

Table 5: Effects of fermented broken rice on the ruminal fermentation parameters of Hu lambs.


       
In accordance with other growth and metabolic indices, all FBR supplementation levels generated similar improvements in ruminal fermentation, with no differences in fermentation parameters among the FBR groups (p>0.05). The results indicated that low-dose FBR supplementation (10 g/d) was sufficient to achieve optimal ruminal fermentation improvement and further dosage increase did not produce additional beneficial effects.
       
Existing research confirmed raw broken rice elevates growth of ducks, piglets, growing pigs and beef cattle (Mateos et al., 2007; Vasupen et al., 2008; Kotupan and Sommart, 2021; Naik et al., 2024). This trial observed higher ADG and lower F/G in lambs fed FBR from day 16 to slaughter, with no growth differences in the initial 15 d. This aligns with the consensus that agricultural by-products require rumen microbial adaptation before delivering growth benefits (Li et al., 2004).
       
The growth-promoting effect of FBR originates from nutritional modification via Lactobacillus acidophilus fermentation (Table 1). Fermentation raised total amino acids from 10.57% to 85.46% and essential amino acids from 0.32% to 3.54%, while anti-nutrient-related crude ash, crude fat and cellulase declined; starch content rose from 84.21% to 88.35% alongside higher fatty acid levels. Lactic acid bacteria secrete amylase and protease to break down crude protein into absorbable small peptides and glutamic acid (Zhuo et al., 2022). These low-molecular nutrients optimize intestinal digestion and raise overall feed utilization (Wang et al., 2020).
       
No growth disparities existed across the 10, 20 and 30 g/d FBR groups, representing a typical plateau effect commonly reported for fermented cereal additives in ruminant studies (Hong et al., 2023). The 10 g/d dosage already satisfies the threshold for optimal rumen function and nutrient utilization; higher supplementation brings no extra nutritional gains and creates unnecessary feed waste, making 10 g/d the cost-effective addition for lamb production.
       
Nutrient digestibility directly reflects digestive capacity and growth potential. Few studies have explored FBR’s influence on Hu lamb digestion, though raw broken rice is proven to boost livestock nutrient absorption (Li et al., 2006). FBR increased OM, CP and NDF digestibility, while DM, EE and ADF digestibility remained unchanged across treatments, consistent with beef cattle results from rice-based diets (Kotupan and Sommart, 2021). Identical digestibility improvements appeared under all three FBR levels, indicating saturated nutrient utilization within the tested dosage gradient.
       
Fermentation degrades macromolecules and anti-nutritional substances in broken rice while accumulating amino acids. Hydrolases produced by lactic acid bacteria split starch and protein into readily digestible fractions to lift CP digestibility and reduced cellulase weakens fiber digestion barriers to raise NDF utilization (Zhuo et al., 2022). Consistent with growth outcomes, digestion efficiency stopped improving when FBR exceeded 10 g/d, verifying the saturation effect of low-dose supplementation.
       
Improved nitrogen retention helps increase protein deposition and cut nitrogen emissions. FBR did not alter nitrogen intake, digestible nitrogen or total nitrogen excretion, yet reduced fecal and urinary nitrogen loss and elevated nitrogen digestibility and retention rate. This matches findings from small ruminants fed fermented rice by-products (Hong et al., 2023; Nguyen et al., 2024), which can be attributed to abundant absorbable amino acids in fermented broken rice.
       
Higher ruminal fermentable starch facilitates microbial protein synthesis (Krause et al., 2002). In this study, FBR raised ruminal NH3-N to supply nitrogen substrates for microbial proliferation. However, NH3-N only serves as an indirect marker of nitrogen metabolism, as this trial did not measure microbial protein yield or flora composition. Lower urinary nitrogen loss may stem from enhanced intestinal amino acid absorption and suppressed hepatic deamination driven by elevated propionate, rather than solely enhanced rumen microbial synthesis (Miyaji et al., 2012).
       
For energy metabolism, FBR exerted no impacts on gross energy intake, digestible energy and related efficiency indicators. Gross energy metabolizability dropped in all FBR groups and only FBR2 had higher urinary energy without regular dosage trends. FBR mainly redistributes nutrients rather than lifting total energy efficiency: extra propionate accelerates hepatic gluconeogenesis and shifts energy toward tissue protein deposition instead of heat dissipation, explaining better growth and nitrogen retention despite lower gross energy metabolizability (Miyaji et al., 2014).
       
Ruminal pH, total VFA and branched-chain fatty acids stayed stable across all groups, meaning FBR would not break rumen homeostasis within the experimental dosage (Kotupan and Sommart, 2021). FBR increased ruminal NH3-N, propionate and butyrate and lowered acetate proportion and acetate-to-propionate ratio, shifting fermentation from fiber-dominated to high-efficiency starch-dominated metabolism. The lower acetate-to-propionate ratio improves energy utilization, while elevated NH3-N supports microbial protein synthesis and fiber degradation, accounting for higher NDF digestibility (Kotupan and Sommart, 2021; Ouyang et al., 2021). Similar VFA regulation effects were recorded in rice feed trials (Zhang et al., 2010).
       
Similar to all growth and metabolic indices, rumen fermentation parameters did not differ significantly among the three FBR dosage groups. Combined with recent studies on fermented cereal by-products in ruminants (Suphra et al., 2019; Hong et al., 2023), this universal plateau effect can be fully explained: low-dose FBR supplementation rapidly optimizes rumen microbial community structure and fermentation function and the rumen microecosystem reaches a stable optimal state. Limited by rumen microbial load and substrate utilization saturation, increasing the supplemental dosage cannot further improve fermentation efficiency, which fundamentally explains the non-dose-dependent changes in growth performance, nutrient digestibility and rumen fermentation indexes in this study.

CONCLUSION

In summary, Lactobacillus acidophilus fermented broken rice optimizes raw rice nutritional profiles by eliminating anti-nutrients and enriching amino acids. FBR improves OM, CP and NDF digestibility, reduces nitrogen excretion and elevates nitrogen retention via modified rumen fermentation, and 10 g/d per lamb is the cost-effective addition for growing Hu lambs. Future studies should focus on multi-omics and targeted microbial detection to further reveal the molecular mechanism by which FBR regulates rumen microecology and nutrient metabolism in ruminants.

ACKNOWLEDGEMENT

We greatly appreciate the support of the China Agriculture Research System of MOF and MARA (Grant No. CARS-38).
 
Data availability statement
 
All data generated or analyzed during this study are included in this published article.
 
Author’s contribution
 
Methodology, software and writing: Q.J. Wu; Data interpretation: Z.B. Zhao; Data collection: Z.M, L.L.Z and J.X. Yang; Formal analysis: R.K. Zhang; Study design: Y.X.Li; Formal analysis: Y. Ma; Literture search, study design: Y.Q. Wang.
 
Ethical statement
 
All the experimental design and procedures involving live animals were approved by the Institutional Animal Care and Use Committee of Henan University of Science and Technology (Record No. IAUC-0586. 2023).
 
Use of artificial intelligence tools
 
No artificial intelligence tools were used for preparation of the work.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

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    Full Research Article

    Effect of Fermented Broken Rice on Growth Performance and Rumen Fermentation Parameters of Hu Lambs

    Q
    Q..J. Wu1
    Z
    Z.B. Zhao1
    R
    R.K. Zhang1
    J
    J.X. Yang1
    Y
    Y.X. Li1
    Y
    Y. Ma1
    Y
    Y.Q. Wang1,*
    1College of Animal Science and Technology, Henan University of Science and Technology, Luoyang 471023, Henan, PR China.

    ABSTRACT

    Background: The experiment was to investigate the effects of fermented broken rice (FBR) supplementation on growth performance, nutrient digestion and metabolism, and rumen fermentation in Hu lambs.

    Methods: A total of 120 weaned Hu lambs were randomly allocated to 4 treatment groups with three replicates per group: a control group fed a basal diet, and three treatment groups supplemented with 10, 20 and 30 g/d FBR per lamb, respectively. The feeding trial lasted 60 days.

    Result: The results showed as follows: compared with the Con group, FBR supplementation increased the average daily gain (ADG) and average daily feed intake (ADFI) of lambs from day16 to 45 (p<0.05), while no differences in ADFI were observed from day 46 to 60. FBR supplementation also markedly improved the apparent digestibility of organic matter, crude protein and neutral detergent fiber, as well as apparent nitrogen digestibility and nitrogen deposition rate, the ruminal ammonia nitrogen, propionic acid and butyric acid contents (p<0.05). Meanwhile, FBR reduced gross energy metabolizability, ruminal acetic acid proportion, and acetate-to-propionate ratio (p<0.05). In conclusion, graded FBR supplementation improves the growth performance of Hu lambs by enhancing nutrient digestibility, regulating energy supply, and optimizing ruminal fermentation characteristics.

    INTRODUCTION

    Broken rice (BR) is a major by-product of rice milling, forming an abundant underexploited agricultural resource suitable for livestock feed. Distince from conventional cereal feeds, BR contains highly digestible starch, crude protein and fiber, alongside bioactive compounds including fatty acids, rice polyphenols, rice bran polysaccharides and γ-oryzanol (Che et al., 2012; Miyaji et al., 2014; Kotupan and Sommart, 2021). These nutrients and bioactive substances endow BR high digestibility and physiological functions, such as antioxidant, anti-inflammatory and immunomodulatory activities, making it an affordable alternative feed material for animal breeding (Nguyen et al., 2022, 2024).
           
    Numerous studies have validated the feeding value of BR for monogastric and ruminant animals. Nutritional analysis shows BR contains 4.2 Mcal/kg digestible energy and 3.7 Mcal/kg metabolizable energy (Miyaji et al., 2012). Adding BR to diets raises total tract and ileal digestibility of gross energy, organic matter and crude fat in weaned pigs (Che et al., 2012). For dairy cows, replacing corn with BR increases ruminal propionate proportion and lowers the acetate-to-propionate ratio to optimize volatile fatty acid composition (Miyaji et al., 2012, 2014). In fattening beef cattle, BR improves rumen fermentation, promotes fatty acid synthesis, raises energy supply and enhances carcass quality (Kotupan and Sommart, 2021). Proper BR addition does not disrupt rumen activity or growth of Hanwoo steers, proving BR is safe and usable for ruminants (Yang et al., 2020).
           
    Despite its nutritional merits, raw BR faces obstacles limiting wide ruminant application. Raw BR has weak structural stability and poor processing performance, coupled with low ruminal starch degradation rate. It also carries anti-nutritional substances such as non-starch polysaccharides, phytic acid, lectins and excess lipase, which reduce feed palatability and nutrient absorption and weaken its feeding value (Wu et al., 2015). Microbial fermentation addresses these drawbacks: it breaks down anti-nutrients, splits large nutrients into readily absorbable small molecules and accumulates functional metabolites, lifting the feeding value of agricultural by-products (Wang et al., 2020; Nguyen et al., 2024).Current BR research mainly focuses on direct feeding for pigs and poultry, while fermented rice by-products are mostly tested on cattle. Few systematic trials have evaluated fermented broken rice (FBR) for sheep production. How FBR regulates lamb growth, whole-body nutrient digestibility and nitrogen metabolism remains unclear, creating an obvious research gap in small ruminant nutrition. The present study hypothesized that dietary FBR supplementation could eliminate the adverse effects of anti-nutritional factors in raw BR, optimize ruminal nutrient digestion and nitrogen retention and improve growth performance of Hu lambs. Therefore, this study was conducted to investigate the effects of FBR on growth performance, nutrient digestibility, nitrogen retention in Hu lambs.
     
    Highlights
     
    1. Fermented broken rice (FBR) supplementation improved growth performance and feed intake of Hu weaned lambs.
    2. FBR increased nutrient digestibility, nitrogen deposition and ruminal glucose, NH3-N, propionate and butyrate  concentrations in Hu sheep.
    3. Dietary FBR reduced gross energy metabolizability, ruminal acetate content and acetate-to-propionate ratio and optimized rumen fermentation profile.

    MATERIALS AND METHODS

    Microbial strain culture and inoculum preparation
     
    The strain used for broken rice fermentation was Lactobacillus acidophilus , purchased from the Central Kay Guangdong Microbial Technology Co., Ltd. (Guangzhou, Guangdong, P.R. China). The strain activation and culture procedures followed standard microbial fermentation protocols described by Wang et al. (2020) with minor modifications. Briefly, the freeze-dried Lactobacillus acidophilus strain was revived and streaked onto Sabouraud dextrose agar (Oxoid Ltd., UK), then statically incubated at 24°C for 7 d to obtain single colonies. Purified colonies were picked and transferred to liquid SDA medium for expanded culture.
           
    A fuchs-Rosenthal hematocytometer was used to count viable bacteria in the inoculant suspension, standardized to 4.8 × 10 CFU/mL. Per unit fermentation substrate required 0.25 g of this bacterial suspension (Cao et al., 2011). Uniform inoculum concentration was applied to all fermentation batches to stabilize fermentation efficiency and eliminate batch differences.
     
    Preparation, fermentation procedures and chemical characterization of fermented broken rice
     
    Broken rice used in this experiment was derived from Yuanyang Rice, a local rice planted in Henan Province, China and freshly harvested in summer 2023. After natural air-drying at 26°C, raw BR was crushed and sieved through a 0.3 to 0.5 mm screens to remove rice husk and bran impurities, improving substrate uniformity and microbial contact during fermentation (Zhang et al., 2010).
           
    Enzymatic saccharification was conducted before fermentation to boost nutrient availability. Food-grade acetic acid adjusted ground BR pH to 5.0; the substrate was heated to 40-50°C, mixed with commercial glucoamylase and held at 60°C to break down macromolecular starch into reducing sugars as carbon sources for microbial growth. Standardized L. acidophilus liquid inoculum was added at 1.5% (v/w). The solid fermentation medium ratio (w/w) was saccharified BR: potato: glucose: agar = 10:1.0:1.0:0.5, supplemented with nutritive salt solution (MgSO4 ·7H2O: (NH4)2SO4: glucose: KH2PO4 = 1:5:6:2). The mixture fermented for 36 h at 28~30°C under natural humidity; this duration was proven optimal for rice by-products to degrade anti-nutrients and accumulate beneficial metabolites in previous research.
           
    FBR was freshly manufactured weekly with a 3000 kg vertical mixer for feeding trials. Each 1500 kg mixed fermentation batch was compacted, sealed in food-grade plastic drums and anaerobically ensiled outdoors at 26~35 °C for no less than 7 d. After ensiling, FBR was air-dried to 950 g/kg DM, ground and sieved through a 0.5 mm mesh for uniform dietary addition. Nutrient profiles of raw BR and FBR were tested before feeding, with compositional changes listed in Table 1. Fermentation lowered anti-nutrient levels and raised crude protein and digestible nutrient contents of BR.

    Table 1: Nutrients and compounds in broken rice before and after fermentation.


     
    Experiment location and animal care
     
    The feeding trial ran from June to August 2023 at Kunyuan Agricultural Cooperative, Henan Province. All animal handling, feeding and sampling procedures obtained approval from the Institutional Animal Care and Use Committee of Henan University of Science and Technology (Approval No. IAUC-0586. 2023) and complied with national standards for laboratory animal welfare.
     
    Lamb, management, experimental diets and experimental design
     
    A total of 120 healthy 60-day-old male Hu lambs with similar initial body weight (19.38±0.98 kg) were randomly allocated to 4 dietary groups in a randomized complete block design. Each group was replicated 3 times with 10 sheep per replicate, fed as follows: (1) Control group (CON): basal TMR diet without FBR; (2) FBR 1 group: basal diet+ 10 g/ day /lamb FBR; (3) FBR 2 group: basal diet + 20 g/ day /lamb FBR; and (4) FBR 3 group: basal diet + 30 g/ day /lamb FBR. The entire experimental period lasted 60 d, including a 45-day formal trial collection period and a 15-day adaptation period. The basal TMR diet was formulated following China Agricultural Standard (NY/T 816-2004)  for mutton sheep feeding and the diet composition and nutrient levels are shown in Table 2.

    Table 3: Effects of fermented broken rice on the growth performance of Hu lambs.


           
    Lambs were housed in independent 4.0 m × 3.0 m pens with free access to feed and water, fed twice daily at 08: 00 and 17: 00. The lambs were fed diets with the same composition and the only difference was the addition of FBR. The FBR was mixed in the basal diet. Daily feed provision and residual feed were recorded at 08:00. Housing temperature maintained at 26°C with daily light duration below 10 h; feeding volume was adjusted according to lamb weight and leftover feed to achieve ad libitum intake.
     
    Sample collection and processing
     
    Lambs were weighed before feeding at 08:00 on days 0, 15, 30, 45 and 60 to calculate ADG. Daily feed supply and residuals were weighed to compute feed intake and F/G ratio. Total feces and urine were collected over days 50 ~ 54 to measure nutrient digestibility, energy metabolism and nitrogen balance. All feed and leftover samples were collected daily, weighed and frozen for 5 consecutive days.

    Feces were fully gathered in stainless steel trays behind tie stalls with separate drainage for urine. Fecal residues were scraped from under lamb hind legs every 4 h and weighed; 50 g/kg of total fresh feces was oven-dried at 65 °C for 48 h, pooled and stored at -18°C. Urine was collected in 5 L plastic containers pre-loaded with 20 mL 50% (wt/wt) sulfuric acid solution, diluted, mixed, subsampled and frozen at -20°C for later analysis.
           
    On day 60, two lambs per replicate were fasted for 12 h and transported to a local abattoir for slaughter. A rumen suction device collected 250 mL ruminal fluid 2 h post-feeding. Ruminal pH was measured immediately with a portable CG840 pH meter (Scho Geräte, Germany). Remaining fluid was centrifuged and preserved in liquid nitrogen for rumen fermentation parameter detection.
     
    Biochemical analysis of samples
     
    The contents of dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE) and total nitrogen (N) in feed, residual feed, feces and urine samples were determined using standard feed analytical procedures. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were measured with an ANKOM 200 Fiber Analyzer by standard fiber analysis protocols. Gross energy (GE) was determined using a PARR-6400 automatic oxygen bomb calorimeter. Ruminal ammonia nitrogen (NH3-N) concentration was determined via phenol-sodium hypochlorite colorimetry and volatile fatty acid (VFA) contents were quantified using a CP 9002 gas chromatograph (Chrompack, Middelburg, Germany).
     
    Statistical analysis
     
    All experimental data were sorted and preprocessed in Excel 2021. Qualified data were analyzed by one-way ANOVA and Duncan’s multiple range test was used for post-hoc multiple comparisons. All statistical analyses were performed using SPSS 26.0 software (SPSS Inc., Chicago, IL, USA). Data were presented as means ± standard error of the mean (SEM). Differences were considered statistically significant at P<0.05.

    RESULTS AND DISCUSSION

    Growth performance
     
    The growth performance of Hu lambs supplemented with different levels of fermented broken rice (FBR) is presented in Table 3. No significant differences were observed in ADG, ADFI and F / G of Hu lambs among all groups in the periods of 0 to 15 d (p>0.05). From day 16 to 30, 31 to 45, 46 to 60 and 0 to 60, lambs receiving FBR had greater ADG and ADFI  and the lower F/G compared with the CON group (p<0.05). No significant differences were detected among the FBR1, FBR2 and FBR3 groups for all growth indices throughout the trial (p >0.05), indicating no obvious linear dose-response relationship within the three FBR addition levels.

    Table 3: Effects of fermented broken rice on the growth performance of Hu lambs.


     
    Apparent digestibility, energy andnitrogen metabolites of dietary nutrients
     
    The effects of FBR supplementation on nutrient apparent digestibility in Hu lambs are summarized in Table 4. Compared with the CON group, FBR supplementation increased the OM, CP and NDF digestibility (p<0.05). The OM digestibility increased from 55.06% in the CON group to 61.84%~63.50% in FBR groups, CP digestibility increased from 60.83% to 67.95%~70.86% and NDF digestibility increased from 58.36% to 66.76%~67.33%. No significant differences were found in the apparent digestibility of DM, EE and ADF among all four groups (p>0.05). Consistent with growth performance results, no differences in nutrient digestibility were observed among the FBR groups (p>0.05) and digestibility did not rise further when FBR addition increased from 10 to 30 g/d.

    Table 4: Effects of fermented broken rice on the nutrients apparent digestibility, energy and nitrogen metabolites of Hu lambs.


           
    No differences were observed in GEI, FE, DE, ME, apparent GE digestibility and DE metabolizability among all groups (p>0.05). UE was higher in the FBR2 group than in other groups (p<0.05), while FBR1 and FBR3 showed no difference compared with the CON group (p>0.05). Notably, the metabolizability of gross energy was decreased in all FBR groups relative to the CON group (p<0.05). Similarly, no progressive dose-response changes were identified among FBR groups for all energy metabolism parameters, demonstrating that increasing FBR dosage did not induce linear alterations in lamb energy metabolism characteristics.
           
    No differences in NI, TEN and DN were detected across all treatments (p>0.05). However, compared with the CON group, all FBR groups exhibited reduced FN and UN excretion (p<0.05), indicating that FBR supplementation reduced nitrogen loss. Furthermore, FBR supplementation improved nitrogen utilization efficiency: ND, ADN and nitrogen deposition rate were higher in FBR groups than in the CON group (p<0.05). No statistical differences were found among the FBRgroups, indicating that all tested FBR dosages effectively enhanced nitrogen retention without significant dose-dependent effects (p>0.05).
     
    Ruminal fermentation parameters
     
    Ruminal fermentation characteristics of Hu lambs were altered by dietary FBR supplementation (Table 5). Ruminal pH, total volatile fatty acid concentration, iso-butyric acid, valeric acid and iso-valeric acid contents remained unchanged among all treatments (p>0.05). Compared with the CON group, FBR supplementation increased NH3-N, propionic acid and butyric acid concentrations (p<0.05), while decreasing acetic acid proportion and the acetate-to-propionate ratio (p<0.05), which optimized ruminal fermentation pattern toward higher energy utilization efficiency.

    Table 5: Effects of fermented broken rice on the ruminal fermentation parameters of Hu lambs.


           
    In accordance with other growth and metabolic indices, all FBR supplementation levels generated similar improvements in ruminal fermentation, with no differences in fermentation parameters among the FBR groups (p>0.05). The results indicated that low-dose FBR supplementation (10 g/d) was sufficient to achieve optimal ruminal fermentation improvement and further dosage increase did not produce additional beneficial effects.
           
    Existing research confirmed raw broken rice elevates growth of ducks, piglets, growing pigs and beef cattle (Mateos et al., 2007; Vasupen et al., 2008; Kotupan and Sommart, 2021; Naik et al., 2024). This trial observed higher ADG and lower F/G in lambs fed FBR from day 16 to slaughter, with no growth differences in the initial 15 d. This aligns with the consensus that agricultural by-products require rumen microbial adaptation before delivering growth benefits (Li et al., 2004).
           
    The growth-promoting effect of FBR originates from nutritional modification via Lactobacillus acidophilus fermentation (Table 1). Fermentation raised total amino acids from 10.57% to 85.46% and essential amino acids from 0.32% to 3.54%, while anti-nutrient-related crude ash, crude fat and cellulase declined; starch content rose from 84.21% to 88.35% alongside higher fatty acid levels. Lactic acid bacteria secrete amylase and protease to break down crude protein into absorbable small peptides and glutamic acid (Zhuo et al., 2022). These low-molecular nutrients optimize intestinal digestion and raise overall feed utilization (Wang et al., 2020).
           
    No growth disparities existed across the 10, 20 and 30 g/d FBR groups, representing a typical plateau effect commonly reported for fermented cereal additives in ruminant studies (Hong et al., 2023). The 10 g/d dosage already satisfies the threshold for optimal rumen function and nutrient utilization; higher supplementation brings no extra nutritional gains and creates unnecessary feed waste, making 10 g/d the cost-effective addition for lamb production.
           
    Nutrient digestibility directly reflects digestive capacity and growth potential. Few studies have explored FBR’s influence on Hu lamb digestion, though raw broken rice is proven to boost livestock nutrient absorption (Li et al., 2006). FBR increased OM, CP and NDF digestibility, while DM, EE and ADF digestibility remained unchanged across treatments, consistent with beef cattle results from rice-based diets (Kotupan and Sommart, 2021). Identical digestibility improvements appeared under all three FBR levels, indicating saturated nutrient utilization within the tested dosage gradient.
           
    Fermentation degrades macromolecules and anti-nutritional substances in broken rice while accumulating amino acids. Hydrolases produced by lactic acid bacteria split starch and protein into readily digestible fractions to lift CP digestibility and reduced cellulase weakens fiber digestion barriers to raise NDF utilization (Zhuo et al., 2022). Consistent with growth outcomes, digestion efficiency stopped improving when FBR exceeded 10 g/d, verifying the saturation effect of low-dose supplementation.
           
    Improved nitrogen retention helps increase protein deposition and cut nitrogen emissions. FBR did not alter nitrogen intake, digestible nitrogen or total nitrogen excretion, yet reduced fecal and urinary nitrogen loss and elevated nitrogen digestibility and retention rate. This matches findings from small ruminants fed fermented rice by-products (Hong et al., 2023; Nguyen et al., 2024), which can be attributed to abundant absorbable amino acids in fermented broken rice.
           
    Higher ruminal fermentable starch facilitates microbial protein synthesis (Krause et al., 2002). In this study, FBR raised ruminal NH3-N to supply nitrogen substrates for microbial proliferation. However, NH3-N only serves as an indirect marker of nitrogen metabolism, as this trial did not measure microbial protein yield or flora composition. Lower urinary nitrogen loss may stem from enhanced intestinal amino acid absorption and suppressed hepatic deamination driven by elevated propionate, rather than solely enhanced rumen microbial synthesis (Miyaji et al., 2012).
           
    For energy metabolism, FBR exerted no impacts on gross energy intake, digestible energy and related efficiency indicators. Gross energy metabolizability dropped in all FBR groups and only FBR2 had higher urinary energy without regular dosage trends. FBR mainly redistributes nutrients rather than lifting total energy efficiency: extra propionate accelerates hepatic gluconeogenesis and shifts energy toward tissue protein deposition instead of heat dissipation, explaining better growth and nitrogen retention despite lower gross energy metabolizability (Miyaji et al., 2014).
           
    Ruminal pH, total VFA and branched-chain fatty acids stayed stable across all groups, meaning FBR would not break rumen homeostasis within the experimental dosage (Kotupan and Sommart, 2021). FBR increased ruminal NH3-N, propionate and butyrate and lowered acetate proportion and acetate-to-propionate ratio, shifting fermentation from fiber-dominated to high-efficiency starch-dominated metabolism. The lower acetate-to-propionate ratio improves energy utilization, while elevated NH3-N supports microbial protein synthesis and fiber degradation, accounting for higher NDF digestibility (Kotupan and Sommart, 2021; Ouyang et al., 2021). Similar VFA regulation effects were recorded in rice feed trials (Zhang et al., 2010).
           
    Similar to all growth and metabolic indices, rumen fermentation parameters did not differ significantly among the three FBR dosage groups. Combined with recent studies on fermented cereal by-products in ruminants (Suphra et al., 2019; Hong et al., 2023), this universal plateau effect can be fully explained: low-dose FBR supplementation rapidly optimizes rumen microbial community structure and fermentation function and the rumen microecosystem reaches a stable optimal state. Limited by rumen microbial load and substrate utilization saturation, increasing the supplemental dosage cannot further improve fermentation efficiency, which fundamentally explains the non-dose-dependent changes in growth performance, nutrient digestibility and rumen fermentation indexes in this study.

    CONCLUSION

    In summary, Lactobacillus acidophilus fermented broken rice optimizes raw rice nutritional profiles by eliminating anti-nutrients and enriching amino acids. FBR improves OM, CP and NDF digestibility, reduces nitrogen excretion and elevates nitrogen retention via modified rumen fermentation, and 10 g/d per lamb is the cost-effective addition for growing Hu lambs. Future studies should focus on multi-omics and targeted microbial detection to further reveal the molecular mechanism by which FBR regulates rumen microecology and nutrient metabolism in ruminants.

    ACKNOWLEDGEMENT

    We greatly appreciate the support of the China Agriculture Research System of MOF and MARA (Grant No. CARS-38).
     
    Data availability statement
     
    All data generated or analyzed during this study are included in this published article.
     
    Author’s contribution
     
    Methodology, software and writing: Q.J. Wu; Data interpretation: Z.B. Zhao; Data collection: Z.M, L.L.Z and J.X. Yang; Formal analysis: R.K. Zhang; Study design: Y.X.Li; Formal analysis: Y. Ma; Literture search, study design: Y.Q. Wang.
     
    Ethical statement
     
    All the experimental design and procedures involving live animals were approved by the Institutional Animal Care and Use Committee of Henan University of Science and Technology (Record No. IAUC-0586. 2023).
     
    Use of artificial intelligence tools
     
    No artificial intelligence tools were used for preparation of the work.

    CONFLICT OF INTEREST

    The authors declare no conflict of interest.

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