Guinea pigs in balance: impact of the probiotic diet on the pH, microbiota and productive performance of guinea pigs

The study was conducted in two phases. In the first phase, the intestinal microbiota was characterised, the pH of the gastrointestinal tract (stomach, duodenum, jejunum, ileum and caecum) was determined, and intestinal morphometric variables were analysed: length, width and density of villi, as well as depth of Lieberkühn crypts in the small intestine. A total of 210 weaned guinea pigs of improved genotype were used, distributed into three dietary treatments: Alf (green alfalfa forage), Alf + BLC (green alfalfa forage plus balanced diet), and BLC (balanced diet). In Alf, 30 guinea pigs were distributed into three groups, and in Alf + BLC and BLC, nine groups/treatment were established, with 10 guinea pigs assigned per group. In the second phase, treatments Alf + BLC and BLC were supplemented with a probiotic mixture enriched with vitamins, minerals and amino acids at three inclusion levels (0, 0.5 and 1%), assigning three groups per level, while T1 remained as a control. The effect of these diets on intestinal morphometry variables and production parameters (feed intake, weight gain and feed conversion) was evaluated. Gastrointestinal pH was measured using a pH meter; microbiota was identified by mass spectrometry, and intestinal morphology was analysed by histological techniques. Results showed significant differences (p < 0.05) in gastrointestinal pH among diets, with concentrate feeding leading to a more alkaline environment. Microbial composition also varied according to diet, with Escherichia coli and Staphylococcus vitulinus predominating after weaning. Intestinal morphology was influenced by both age and type of diet, with probiotic supplementation enhancing villus length and density in the small intestine, while higher doses increased villus depth. Productive performance improved in guinea pigs receiving a mixed diet with 0.5% fortified probiotics, which showed greater weight gain, feed intake and better feed conversion. In conclusion, dietary composition and probiotic supplementation modulated gastrointestinal conditions, microbial communities and intestinal structure, resulting in improved growth performance. These findings suggest that gastrointestinal pH influences microbial composition, productive efficiency, and immune health, highlighting the importance of balanced nutrition and the use of probiotics to optimise health and performance in production guinea pigs.

1 Introduction

The relationship between diet and animal health, as well as the interaction between gastrointestinal microbiota and metabolism, has been studied for decades and remains a highly relevant topic in the field of animal production (Al et al., 2017). In this context, guinea pigs (Cavia porcellus) have emerged as a valuable model due to their herbivorous nature and widespread use in meat production in Andean countries (Frías et al., 2023), particularly in Ecuador, Bolivia, and Peru, where guinea pig meat is an important source of animal protein (Buela et al., 2022). It is considered an attractive meat and a non-traditional alternative food source that can be incorporated into the gastronomic market (Vargas et al., 2020). In Ecuador, it is regarded as a food of high biological value and excellent flavour, contributing to food security and sovereignty among the rural population, where per capita consumption is recorded at 16.90 kg/year, compared to 8.52 kg/year in urban areas (Reyes et al., 2021).

Diet plays a crucial role in productive performance and significantly influences the modulation of the gut microbiota (Miranda-Yuquilema et al., 2025) and the physiological and metabolic processes of animals, with fibre being a key nutrient for maintaining the diversity of the gut microbiota (Cuenca et al., 2022). However, in guinea pigs, in hast not yet been clearly established how variations in diet composition and probiotic supplementation modify gastrointestinal pH and gut microbiota structure, nor how these changes relate to productive efficiency and gut health. This lack of evidence represents a significant gap in knowledge, considering that guinea pigs are monogastric herbivores with digestive characteristics that cannot be directly extrapolated from models such as rabbits or pigs.

It has been documented that the diet offered to animals can change the pH in different regions of the gastrointestinal tract by modulating the composition and activity of the gut microbiome (Álvarez et al., 2018). For example, a diet rich in fibre can favour a more acidic pH in the caecum, promoting the growth of beneficial bacteria such as Lactobacillus and Bifidobacterium (Jha et al., 2019; Zhu et al., 2024). On the other hand, diets with high levels of undigested starch can lead to excessive fermentation in the caecum, resulting in a drastic decrease in pH and altering the stability of the microbiota (Xiccato et al., 2010; van der Sluis et al., 2024). This interaction between diet and pH is especially relevant in herbivorous species such as guinea pigs, whose digestive system is adapted to process large amounts of fibre (Cuchillo et al., 2024).

Gastrointestinal pH affects microbial composition, nutrient absorption capacity and immune function (Vásquez et al., 2012). In small herbivores, such as guinea pigs, suboptimal pH can compromise fibre digestion and fermentation, decreasing feed efficiency and productive performance (Kawasaki et al., 2018). Although studies in rabbits show that diets with fermentable fibre stabilise caecal pH and, optimise nutrient conversion, information on guinea pigs is scarce and fragmented, particularly regarding the morphological response of the digestive tract and its relationship with probiotic supplementation (Lindberg, 2014). In contrast, in non-herbivorous monogastric, protein-rich diets induce an alkaline pH at the caecal level, which promotes intestinal health and productive parameters (Céspedes et al., 2023).

Probiotics have been proposed as a biotechnological tool capable of increasing animal productivity by improving intestinal health, digestion and nutrient absorption, and modulating the microbiota (Icaza, 2013; Duncan et al., 2008; Miranda et al., 2024; Alvarado and Hernández, 2024). In the 1960s, it was scientifically proven that Lactobacillus strains improve growth performance in monogastric animals; Therefore, the most commonly used probiotics in monogastric animals are yeasts (Saccharomyces boulardii and S. cerevisiae) and bacteria (Lactobacillus spp., Enterococcus spp., Pediococcus spp., Bacillus spp.) that act in the caecum and colon (Carcelén et al., 2020). However, few studies have comprehensively evaluated the effect of probiotic inclusion on gastrointestinal pH, microbiota, and production parameters in guinea pigs fed different dietary bases, which limits the formulation of specific nutritional strategies for this species.

In this context, the present study aimed to evaluate the impact of three types of diets: green alfalfa forage (Alf), green alfalfa forage supplemented with a balanced diet (Alf-BLC), and balanced diet (BLC), with the inclusion of a probiotic mixture -Probiolyte^® WS (0, 0.5 and 1.0%) on gastrointestinal pH, intestinal microbiota composition, digestive tract morphometry and productive performance in guinea pigs. The results of this research seek to fill the existing gap in knowledge regarding the relationship between diet, modulation of the intestinal environment, and productivity in guinea pigs, providing scientific evidence applicable to the development of more sustainable and healthier production systems.

2 Materials and methods

2.1 Study area and distribution of experimental units

The study was carried out in Cuenca, Ecuador, located at an altitude of 2,500 metres above sea level and an average annual temperature of 14.6 °C [Planning Council of the Cuenca Canton (2022)].

In the first phase of the study, 210 weaned guinea pigs (21 days old), with an improved genotype were used. After feeding at midday, the animals were weighed, showing an average body weight of approximately 351 ± 25 g for males and 307 ± 25 g for females. They were randomly distributed into three dietary treatments: T1- Green alfalfa forage (Alf), T2 - Green alfalfa forage + Balanced diet (Alf + BLC) (80% forage and 20% concentrate) and T3 - Balanced diet (BLC). In treatment T1, 30 guinea pigs were used, organised into three groups of 10 animals (9 females and 1 male). In treatments T2 and T3, 90 guinea pigs were used per treatment, distributed into nine groups of 10 animals (9 females and 1 male) each.

In the second phase, based on the results of the previous phase, where 24 female guinea pigs (2 per group in T1, n = 6; and 1 per group in T2 and T3, n = 18) were sacrificed for the identification of the microbiota, the measurement of intestinal morphometry variables and the evaluation of the dietary effect on gastrointestinal pH; a commercial probiotic mixture enriched with vitamins, minerals, and amino acids was incorporated into treatments T2 and T3 at three inclusion levels (0%, 0.5%, and 1%) to analyse its interaction with the basal diets. The inclusion levels were established according to the manufacturer’s recommendations and previous studies in guinea pigs and other small herbivores. No probiotics were added to the group fed exclusively on green alfalfa forage (T1), which was considered a negative control and represented the traditional feeding system in Andean rural production.

2.2 Description of the feeding method

During the growth phase (22–60 days of age), the animals were fed 12% dry matter (DM) based on the live weight (LW) of the animal while during the fattening phase (61–90 days of age), they were fed 10% DM/LW.

The total daily DM requirements of the animals were calculated using the following formula:

$$\text{DM total required (g)}=LW (g) X (\frac{\% DM}{100})$$

The total DM requirement in T2 Alf + BLC) was distributed proportionally: 80% Alf and 20% BLC using the following calculation methodology:

✓ DM Alf, g = DM total X 0.80.

✓ DM BLC, g = DM total X 0.20.

Subsequently, the amount of DM was converted to fresh weight (offered), considering the DM content of each feed: Alf (21%) and BLC (88%). The formulas used were:

$$FW Alf (g)=\frac{\text{Total DM Alf }(\text{g})}{0.21}$$

$$FW BLC (g)=\frac{\text{Total DM BLC }(\text{g})}{0.88}$$

Practical example:

For a guinea pig with a live weight of 400 g during the fattening stage (10% DM):

Total DM Requirement: 400 X 0.10 = 40 g of DM.

Distribution of DM between Alf and BLC:

Alf of DM (80%): 40 X 0.80 = 32 g of DM.

BLC of DM (20%): 40 X 0.20 = 8 g of DM.

Conversion to Fresh Weight:

Alf: 32/0.21 = 152.4 g.

BLC: 8/0.88 = 9.1 g.

Therefore, the daily feed supply per guinea pig consisted of approximately 152.4 g of green alfalfa forager (edible parts) and 9.1 g of concentrate, ensuring the nutritional requirements based on dry matter (DM) and maintaining the 80:20 ratio established for the mixed diet.

2.3 Experimental diet formulation and nutritional characterization

The animals selected for the experiment underwent an adaptation period (seven days) during which behavioural changes and normal food consumption were monitored. After this period, animals that showed no behavioural changes continued to receive the diet according to the assigned group. Table 1.

Table 1

Table 1. Nutritional composition of diets.

2.4 Zootechnical management of the guinea pigs

The guinea pigs were individually identified using numbered metal ear tags placed on the left ear. All animals were housed in a shed under controlled environmental conditions, with an average temperature maintained between 18–22 °C and relative humidity ranging from 60% to 70%. A 12-hour light/12-hour dark photoperiod was ensured through natural lighting, supplemented with artificial light when necessary.

The animals were housed in breeding cages measuring approximately of 1.2 m long × 1.0 wide × 0.5 m high, in accordance with recommendations for guinea pigs in the fattening phase. Plastic Feeders and drinkers specifically designed for guinea pigs were used; the feeders allowed easy access to clean feed, while the mini drinkers ensured a continuous supply of clean water.

The feeding programme was administered twice a day, at 08:00 and 16:00, adjusted according to the nutritional requirements corresponding to each physiological stage of the animals. Health, hygiene and biosecurity measures were applied uniformly across treatments, in compliance with animal welfare guidelines and with the aim of minimising stress throughout the experimental period.

2.5 Obtaining samples from the gastrointestinal tract of guinea pigs

Following approval of the experimental protocol by the Bioethics Committee for the use of animals in teaching and research of the Instituto Superior Tecnológico del Austro (CBEISTA/2024/001; 10-01-2024), the specimens to be euthanised were randomly selected. In the first phase of the study, the guinea pigs were euthanised seven days after the adaptation period to the experimental diets. Six females were selected from treatment T1 (n = 2 per group) and nine females per treatment in T2 and T3 (n = 1 per group). At the end of the second experimental phase (61–90 days of age), two females per group were selected in each treatment.

These were subjected to 12 hours of fasting before euthanasia, which was carried out following the recommendations for experimental animals (rodents) described by Gimeno et al. (1990), Close et al., 2011. This protocol was applied in replacement of the specific regulations for the euthanasia of rabbits and other rodents established in the Mexican Official Standard NOM-033-ZOO-1995, Humane Slaughter of Domestic and Wild Animals (American Veterinary Medical Association, 2016).

2.5.1 Evaluation of pH in digestive tract segments

After the guinea pigs had adapted to the diet (7 days), the pH was measured in the different segments of the gastrointestinal tract (stomach, duodenum, jejunum, ileum and caecum)- The measurements were taken immediately after euthanasia and within the first 10 minutes after sacrifice, in order to avoid post-mortem alterations in pH values (Figure 1). For this purpose, a portable pH meter (Hanna^®, Pandova, Italy) was used, following the methodology described by Miranda et al. (2024).

Figure 1

Figure 1. Schematic diagram of sampling points within the gastrointestinal tract of guinea pigs and the variables evaluated.

2.5.2 Histological and morphometric evaluation of the small intestine in guinea pigs

Tissue samples from segments of the small intestine (duodenum, jejunum, and ileum) were analysed for histological and morphometric evaluation. The length and width of the villi (μm) were measured, as well as the depth of the intestinal crypts (μm). Measurements were taken on at least eight intact and well-oriented villi per segment, selected according to the following criteria: continuous epithelium, absence of structural damage, and orientation perpendicular to the axis of the lamina propria.

The morphometric reference points were defined as follows: villus length was measured from the apical tip to the base at the junction with the crypt; villus width was determined at the midpoint of its length; and crypt depth was measured from the base of the villus to the lower limit of the intestinal gland.

Observations were made using an Eclipse Ci-L microscope (Nikon, Tokyo, Japan) with 100× to 300× objective lenses, together with an image analysis system on a digital camera (Olympus DP72, Olympus, Belgium). The procedure was carried out following the methodology described by Miranda et al. (2024).

2.5.3 Identification of the intestinal microbiota in guinea pigs

The microbiota of the suckling guinea pigs was analysed by rectal swabbing. The samples were placed in Stuart transport medium (DELTALAB^®, Spain) and immediately transferred to the laboratory within a maximum of two hours for processing.

For the guinea pigs subjected to the three initial treatments, the microbiota was identified from samples of intestinal mucus, obtained by a 2 cm² longitudinal incision in the stomach, small intestine, caecum and colon. The tissue fragments were washed with distilled water and physiological saline solution before analysis.

Subsequently, with the aid of a 75 mm spatula, deep scraping was performed until 1.00 mL of intestinal mucus was obtained. These were stored in 10 mL Falcon tubes (Sterile falcon, Greiner, Germany) with a sterile screw cap and buffered with 5.00 mL of BFS according to the methodology described by Kandler and Weiss (1992). Finally, they were centrifuged (digital centrifuge, Yingtai, China) at 4582 × g at 8 °C for 10 min and the supernatant was removed; this procedure was performed three times. Next, in a 100 mL Erlenmeyer flask with 50 mL of nutrient broth, 1.00 mL of previously obtained sample was added, separately and independently of each organ, and immediately incubated at 37 °C for 6 h in an incubator with an orbital shaker (Inkubationshaube TH 15, GmbH, Bodelshausen, Germany) at 15 rpm. After this time, 5.00 mL of each culture were taken and homogenized with physiological saline solution at a 1/10 (v/v) ratio, followed by serial dilutions of 1/10, (v/v) to the 0.5 scale of the MacFarland scheme.

Identification via Matrix-Assisted Laser Desorption/Ionisation–Time of Flight Mass Spectrometry (MALDI-TOF) was performed following the protocol described by García et al. (2012), starting from a single isolated colony of the microorganism under investigation. Colonies were applied onto a polished metal target plate, which accommodates between 96 and 384 samples for simultaneous analysis in a single run.

A saturated matrix solution containing α-cyano-4-hydroxycinnamic acid, acetonitrile, and trifluoroacetic acid was applied directly onto the colonies. This matrix facilitates the disruption of the cellular membrane, releasing intracellular proteins and enabling their desorption and ionisation by a pulsed laser beam. The sample is subsequently air-dried at room temperature until crystallisation is achieved.

Once ionised, the protein fragments travel through a vacuum tube, where they are detected at the end of their flight. The time taken—referred to as the “time of flight”—is determined by the mass-to-charge ratio (m/z) of each protein fragment, allowing for the construction of a characteristic mass spectrum. The spectrum is then processed by the analytical software, which automatically compares it to a reference database to identify the microorganism.

When using Bruker systems, the identification results are provided with a score. A score ≥2.0 indicates reliable identification at both genus and species level; scores between 1.7 and 1.9 permit identification at genus level only; while scores <1.7 are considered insufficient for accurate identification (Di Conza, 2022).

2.6 Data analysis

All data were analyzed using the statistical software InfoStat. In the first phase of the study, the Shapiro-Wilk test was applied to assess the normality of each variable. For normally distributed variables—such as gastrointestinal pH and intestinal morphometry, analysis of variance (ANOVA) was used to compare the means among the three dietary treatments (Alf, Alf + BLC, and BLC). For nonparametric variables, the Kruskal-Wallis test was applied to compare the medians. All statistical analyses were performed with a 95% confidence level.

In the second phase, a two-way factorial ANOVA was performed to assess the effects of diet type (Alf, Alf + BLC, and BLC), probiotic supplementation (0, 0.5 and 1%) and their interaction, on gastrointestinal Ph and dependent variable of gastrointestinal pH and intestinal morphometry. Multiple comparisons were conducted using Tukey’s post hoc test.

Additionally, a nested factorial design was applied to more actcurately characterise the effect of probiotic supplementation within each diet type. In this model, diet was defined as the main factor, and probiotic level (0, 0.5, and 1%) as the nested factor, included only in diets T2 (Alf + BLC) and T3 (BLC). Diet T1 (ALF) was evaluated exclusively with a 0% probiotic level to avoid inappropriate comparisons between non-equivalent treatments. Additionally, intestinal segment (duodenum, jejunum, and ileum) was incorporated as an additional source of variation, along with the Diet × Segment interaction. This allowed for the detection of morph functional differences associated both with diet type and anatomical location within the intestine.

To evaluate the composition of the intestinal microbiota, a relative frequency analysis was performed, based on the proportion of each bacterial species relative to the total number of bacteria isolated. The relative frequency (RF) was calculated using the formula:

$$RF=\frac{\text{Number of occurrences of a species}}{\text{Total number of occurrences}}$$

This approach, adapted from Sánchez et al. (2022), allowed for the assessment of bacterial prevalence across treatments, ensuring a statistically valid representation of the microbial composition.

Additionally, Pearson correlation analysis was used to assess the relationship between gastrointestinal pH and morphometric parameters in each intestinal segment. A linear regression model was then applied to determine how the independent variables (diet, gastrointestinal pH, and microbiota composition) influenced the dependent variables (production parameters and intestinal morphometry). In all cases, a (p < 0.05) was considered statistically significant.

This comprehensive analytical approach ensured that all dependent variables were accurately assessed in relation to dietary and probiotic factors, maintaining consistency and methodological rigour throughout the study.

3 Results

3.1 Gastrointestinal pH

The gastrointestinal pH in guinea pigs fed different diets showed statistically significant differences (p < 0.05) across the various segments analysed. Guinea pigs fed a green alfalfa forager-based diet exhibited the highest stomach pH (5.88). In contrast, those fed a balance diet-based diet displayed the highest pH values in the duodenum (7.13) and jejunum (8.38). No statistically significant differences (p > 0.05) were observed in the pH levels of the ileum and caecum based on diet type. The data are presented in Table 2.

Table 2

Table 2. Gastrointestinal pH across different treatments.

3.2 Identification of intestinal microbiota

A total of 17 bacterial species were identified in the faecal microbiota of lactating guinea pigs, with Staphylococcus vitulinus and E. coli being the most prevalent. These bacteria belong to the phyla Firmicutes and Proteobacteria, respectively. In weaned guinea pigs assigned to the Alf+BLC and BLC treatments, a total of ten bacterial species were identified, with E. coli being predominant. See Tables 3 and 4.

Table 3

Table 3. Intestinal microbiota of lactating guinea pigs.

Table 4

Table 4. Intestinal microbiota of guinea pigs supplemented with a reinforced probiotic mixture.

3.3 Intestinal morphometry

Significant differences (p < 0.05) were observed between treatments, and age was also found to influence intestinal morphometric variables, which increased with age. Mixed feeding with the addition of 0.5% of the enhanced probiotic blend (Probiolyte^® WS) significantly increased villus length in the duodenum (538 µm) and ileum (294 µm), as well as villus density in the duodenum (67 per field at 4X). Mixed feeding with the addition of 1% improved villus width in the duodenum (56.9 µm) and villus depth in the ileum (48.9 µm). Guinea pigs fed with concentrate exhibited increased villus length in the jejunum (434 µm) and villus width in the ileum (51.9 µm). Feeding with concentrate and the addition of 1% of the enhanced probiotic blend improved villus depth in the jejunum (52.9 µm). These findings suggest that the combination of highly available nutrients and the microbial modulation induced by probiotics promotes the integrity and development of the intestinal mucosa, optimizing epithelial turnover and absorptive capacity across the different segments of the small intestine. See Table 5.

Table 5

Table 5. Effects of diet, probiotic level and intestinal segment on intestinal morphometric variables in guinea pigs.

3.4 Productive parameters

The productive parameters such as weight gain (WG), feed intake and feed conversion ratio (FCR) showed a significant difference (p < 0.05) between treatments. The guinea pigs fed with a mixed diet plus 0.5% of the reinforced probiotic blend reached the highest WG (284.67 g), the highest feed intake (1046.08 g), and the best FCR (3.70) by the seventh week of the study, compared to the other treatments. See Table 6.

Table 6

Table 6. Productive performance of experimental guinea pigs.

3.5 Correlation analysis

The correlation analysis suggests that pH has a variable influence on the morphometric characteristics of intestinal villi depending on the segment of the digestive tract. In the jejunum and ileum, pH shows a stronger association with villus length and width, whereas in the duodenum, its influence is more limited. These findings highlight the importance of considering the specific segment when evaluating the impact of pH on intestinal morphometry. See Table 7.

Table 7

Table 7. Correlation between gastrointestinal pH and intestinal morphometry.

4 Discussion

4.1 Gastrointestinal pH

The gastrointestinal pH values recorded in this study across different gut segments of guinea pigs reflect a dynamic internal environment that may significantly modulate enzymatic activity and microbial composition. The acidic pH observed in the stomach aligns with conditions conducive to initial protein digestion and pepsin activation. As chyme progresses towards the small intestine and caecum, the transition to a more neutral or slightly alkaline pH supports the activity of lipases and cellulases—key enzymes for fibrous plant material degradation (Merchant et al., 2011; Rechkemmer et al., 1986).

The findings suggest that the administered diet and the inclusion of fermented bioadditives containing lactic acid bacteria (LAB) and yeasts contributed to pH stabilisation along the gastrointestinal tract. This, in turn, likely promoted a more diverse and functional microbiota. Organic acids such as lactic and acetic acid, produced by these microbes (Miranda et al., 2022; Goicochea et al., 2024), may have contributed to a mildly acidic luminal environment, potentially inhibiting pathogenic bacteria at pH ≤ 4 while supporting beneficial bacterial populations (Pinchao et al., 2024).

The pH levels reported by Ramón (2017); García et al. (2019), and Vásquez et al. (2012) in guinea pigs and alpaca calves illustrate species-specific and age-related differences, highlighting how dietary composition, feeding frequency, and physiological status influence gastrointestinal pH regulation.

4.2 Identification of the intestinal microbiota

This study identified dominant bacterial genera associated with fibre degradation and bioactive metabolite production. The detected microbial profile suggests a functional symbiosis between the host and its microbiota, wherein intestinal pH and diet act as selective pressures shaping microbial diversity and activity.

The prevalence of LAB and butyrate-producing bacteria, including strains isolated by Pinchao et al. (2024), correlates with enhanced mucosal integrity and improved nutrient absorption. These microbial taxa are likely contributors to the improved morphometric and productive parameters observed in treated animals. Our results also complement the findings of Wu et al. (2014); Murga et al. (2020), and Hildebrand et al. (2012), where dominant phyla such as Firmicutes and Bacteroidota were linked to digestive health.

In addition, Frías et al. (2023) noted that host genetics influenced caecal microbiota composition in different guinea pig breeds, a hypothesis supported here by the consistent microbial profiles within treatment groups. While previous studies have yielded conflicting results (Alayande et al., 2020), our findings reinforce the idea that targeted modulation of the microbiota through dietary interventions can produce measurable functional outcomes.

4.3 Intestinal morphometry

Morphometric changes observed in the intestinal villi, including increased villus height and width and improved crypt-villus ratios, indicate a responsive epithelial structure to microbial modulation and luminal conditions. These results are consistent with previous work by Carcelén et al. (2020) and Puente et al. (2019), who observed similar benefits following probiotic supplementation in guinea pigs.

In the present study, groups supplemented with fermented bioadditives exhibited superior mucosal development. This may be attributed to the production of trophic factors such as short-chain fatty acids—especially butyrate—by beneficial microbes, which promote epithelial cell proliferation and tissue repair.

4.4 Productive parameters

The relationship between a stable gut environment (reflected by moderated pH), a beneficial microbial community, and a functional intestinal morphology translated into improved productive performance. Animals receiving fermented bioadditives showed higher weight gain and feed efficiency, likely due to more efficient digestion and absorption (Table 6).

These findings support the hypothesis that dietary strategies targeting the gut ecosystem can enhance productivity in guinea pigs. The combination of LAB and yeast in fermented substrates appears particularly effective. This contrasts with previous reports of inconsistent results (Valdizán et al., 2019; Carcelén et al., 2020; Guevara et al., 2021; Criollo et al., 2019), suggesting that the formulation and microbial viability of bio additives are critical to their success.

Our data also align with Miranda et al. (2024) and Cuenca et al. (2022), who found that bio additives improve feed intake, carcass traits, and overall productivity in guinea pigs.

Taken together, the results of this research confirm the positive interaction between diet, gut microbiota, and productive efficiency in guinea pigs, demonstrating that fermented bioadditives represent a viable biotechnological alternative for optimizing zootechnical performance. However, certain limitations of this study must be acknowledged, including the sample size and the lack of high-resolution metagenomic analyses that would allow for a more in-depth characterization of the microbiota. Future research should increase the number of animals, incorporate advanced molecular techniques (e.g., next-generation sequencing), and evaluate the long-term persistence of the observed effects. These considerations will strengthen our understanding of the interactions between nutrition, microbiota, and intestinal physiology in this model species.

5 Conclusions

This study demonstrated that dietary supplementation with fermented bio additives significantly influenced gastrointestinal pH, intestinal microbiota composition, intestinal morphometry, and productive performance in guinea pigs. Specifically, animals receiving the supplemented diet showed more stable pH values along the gastrointestinal tract, a higher relative abundance of lactic acid bacteria and butyrate-producing genera, increased villus height and width, and improved feed conversion and weight gain compared to the control group.

These findings confirm the initial hypothesis that targeted dietary interventions can modulate digestive physiology and gut microbial communities to improve nutrient absorption and animal performance. The results offer practical implications for enhancing guinea pig production systems through nutritional strategies that promote digestive efficiency and intestinal health.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement

The animal study was approved by The animal study protocol was approved by the Institutional Review Board of Instituto Superior Tecnológico del Austro (protocol code CBEISTA/2024/001). The study was conducted in accordance with the local legislation and institutional requirements.

Author contributions

MC-C: Funding acquisition, Supervision, Project administration, Validation, Conceptualization, Writing – review & editing, Data curation, Writing – original draft, Methodology, Investigation, Software, Resources, Formal analysis, Visualization. NC-M: Validation, Supervision, Writing – review & editing, Conceptualization, Data curation, Methodology, Writing – original draft, Investigation, Resources, Formal analysis, Visualization, Software. WQ-R: Supervision, Writing – original draft, Formal analysis, Resources, Methodology, Visualization, Conceptualization, Investigation, Validation. JM-Y: Data curation, Resources, Validation, Visualization, Investigation, Writing – review & editing, Formal analysis, Methodology, Software.

Funding

The author(s) declared that financial support was received for this work and/or its publication. The project, code (PIFCV22-74): (Probiotics as an alternative replacement for growth-promoting antibiotics in animal production systems), was funded through an official call by the Formative Research Area of the Catholic University of Cuenca.

Acknowledgments

Sixth cycle students of Medicina Veterinaria – Universidad Católica de Cuenca-Ecuador, March-August 2024 cycle.

Conflict of interest

The authors declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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