The use of unregulated feed additives in intensive poultry farming provides essential growth stimulation but carries significant risks, including potential health problems for birds and damage to the industry’s long-term sustainability and public confidence (Karthika et al., 2019; Mirsalami et al., 2024).
       
Inadequate nutrition negatively affects zootechnical performance, reducing growth rates and meat and egg quality, while increasing mortality (WOAH, 2022). The use of organic products such as probiotics, which support intestinal health and optimize digestion, is therefore essential for the development of the industry, as it improves animal health and increases productivity in a sustainable manner (Abbad et al., 2024; Kumar et al., 2025; Thangadurai et al., 2024).
       
The introduction of probiotics based on lactic acid bacteria (LAB) into chicken feed is an effective scientific strategy for improving zootechnical performance and poultry health (Chai et al., 2023; Monika et al., 2024). These live microorganisms, introduced as feed additives, act by restoring and maintaining a healthy intestinal microbiota, thereby promoting nutrient absorption, better metabolic health and reducing the prevalence of pathogens (Li et al., 2018). The effectiveness of LAB lies in their ability to produce short-chain fatty acids (SCFAs) and modulate intestinal immunity, resulting in improved feed efficiency and increased growth in birds (Kumar et al., 2025; Thangadurai et al., 2024).
       
Research in Algeria demonstrates that adding probiotics like Lactobacillus acidophilus to broiler feed improves poultry health and performance by enhancing growth, optimizing digestion and nutrient absorption through a balanced gut microbiome and strengthening the immune system, all of which can reduce the need for antibiotics. This suggests a sustainable and efficient farming strategy and the specific study aims to measure the effects of L. acidophilus supplementation on zootechnical performance, gut health and blood profiles.

Ethical statements
 
The study was conducted in accordance with the regulatory framework defined by the Regional Committee for Ethical Review of Animal Experiments (RCERAE) 2024. The approval number is 26/RCERAE-25/10/2024 (project code in 03 repetitions of breeding Cobb 500 broiler chickens, a fast-growing broiler hybrid developed for high production performance. The project reference is PLSTPA3/2024/Team 2-4, duration: from 03/11/2024 to 13/12/2024 for the first breeding, from 05/01/2025 to 14/02/2025 for the second breeding and from 15/03/2025 to 24/04/2025 for the third breeding. This approval complies with in vivo experimental guidelines, ensuring compliance with ethical and publication standards in the field of animal experimentation.
 
Probiotic preparation procedure
 
A Lactobacillus acidophilus master culture was reactivated using a two-stage process involving incubation in MRS broth (BIOKAR Diagnostics-Solabia, Brazil) and spreading on plates, following the work of Dahou et al., 2016 and Tabet et al., 2025. A pure colony was isolated, subcultured and used to create a 1% inoculum for probiotic production. To isolate the probiotic suspension, the culture was centrifuged to form a pellet and the supernatant was filtered through a 0.22 µm filter to remove cells and debris before being stored at 4°C. This specific strain was later confirmed to have probiotic potential through in vitro studies, which showed resistance to acid and bile salts and the ability to inhibit pathogenic bacteria. A daily dose of Lactobacillus acidophilus probiotic (viability of 10⁸ CFU/ml) is given to chicks through their drinking water. The probiotic is prepared daily as a premix at a concentration of 0.1 to 0.3% based on the chicks’ water consumption, then added to water and distributed in low drinkers between 6:30 and 7:30 a.m.
 
Basic feed
 
The basic feed for Cobb 500 broiler chickens is composed of the following percentages for the pre-starter, starter and finisher phases:
Crushed corn: 56.85
Soybean meal: 35.15
Soybean oil: 4.65
Calcite: 1.25
Dicalcium phosphate: 1.25
Salt: 0.2
L-Lysine: 0.25
DL-Methionine: 0.34
Vitamins A, D3, E and K: 0.02
Water-soluble B complex vitamins and vitamin C: 0.02
Trace elements: 0.02

Zootechnical performance
 
Feed conversion efficiency: Feed intake and body weight
 
A representative sample of chickens from different areas of the farm is taken according to the protocol developed by the LSTPA laboratory research team. A minimum sampling rate of 5% is often recommended to obtain a reliable average. The selected chickens are gathered and placed in pens for easy transport to the scales. For weighing, each chicken is quickly placed on the scales to avoid stressing the animals and to obtain the most accurate weight possible. The data obtained is recorded on a tracking sheet. The average weight of the group is obtained by adding up all the recorded weights and dividing by the number of chickens weighed. The average daily gain (ADG) is calculated by dividing the total weight gain by the number of days of growth. This gives an indication of the growth rate. To determine consistency, weigh the same sample of chickens regularly, usually every week, to monitor weight gain and the effectiveness of your feed. To avoid irregularities in weight gain, ensure that the rearing environment is optimal (temperature, ventilation).
       
The feed conversion ratio (FCR) of a group of broiler chickens at 40 days is measured by recording the total amount of feed consumed and the total weight of the chickens at that age (Steenfeldt et al., 2019). The formula used is as follows:

The objective of this monitoring is to obtain the lowest possible FCR, which indicates greater production efficiency.
 
Carcass evaluation
 
Twenty-four Cobb 500 broiler chickens (aged 40 days, divided into a control group n=6, Group 1 and an experimental group n=18 divided into 3 batches of 6, Group 2) were subjected to a 12-hour water fast prior to slaughter. Slaughter was performed according to the standardized protocol of the LSTPA laboratory. The live weight (LW) of each animal was measured individually with an accuracy of 0.1 g. For post-mortem evaluation, the weight of each organ (heart, liver, gizzard, etc.) was determined. The percentage of each organ’s weight relative to live weight was calculated in Microsoft Excel 2013 using the formula ensuring clarity and reproducibility of data.:

 
Assessment of broiler health by blood biochemistry
 
To assess the metabolic status of two groups of clinically healthy broilers, blood biochemical parameters (cholesterol, triglycerides, glucose) were determined. Blood samples were collected by venipuncture (right jugular vein), placed in vacuum tubes containing an anticoagulant (heparin) and then centrifuged to obtain plasma, which was frozen at -20°C until analysis on a SIEMENS HEALTHINEERS ATELLICA analyzer. This methodology complies with the recommendations of the World Organization for Animal Health (EFSA, 2023 and WOAH, 2022).
 
Statistical analysis
 
The analysis of experimental data, evaluating the impact of probiotic supplementation on the health and zootechnical parameters of broiler chickens, was performed using IBM SPSS Statistics software version 30 (2025). Given the comparison of two treatment groups, a Student’s t-test for independent samples was applied. The homogeneity of variances was previously verified using Levene’s test. Differences were considered statistically significant at a threshold of P≤0.05.

Zootechnical performance
 
Feed conversion efficiency: Feed intake and body weight
 
The evaluation of zootechnical performance shows that the incorporation of probiotics in drinking water significantly improved the growth parameters of broiler chickens compared to the control group (p<0.05). The experiment, conducted on two separate groups-group 1 (control) without additives and group 2 (experimental) receiving gradual doses of 0.1%, 0.2% and 0.3%-shows a marked superiority of the supplemented group (Table 1).


       
The best results were recorded with a dosage of 0.2%, showing a maximum final live weight of 3210 g, followed respectively by doses of 0.3% and 0.1%. This 0.2% diet also optimized feed efficiency, with the highest average daily gain (ADG) (79.05 g/day) and the lowest Feed Conversion Ratio (FCR) (1.51). In contrast, the control group performed less well, with a final weight of 2510 g, an ADG of 61.55 g/day and a FCR of 2.04 (Table 1 and Fig 1). This improvement suggests that the 0.2% concentration is the optimal threshold for maximizing feed conversion and weight gain in broiler chickens.


 
Detailed performance
 
Supplementing broiler feed with 0.2% probiotics significantly improved growth and feed efficiency compared to the control group, resulting in higher final body weight (3210 g vs. 2510 g), increased average daily gain (79.05 g/day) and a lower, more efficient feed conversion ratio (1.51vs.2.04). While feed intake was slightly higher for the control group, the probiotic group used feed more efficiently due to improved nutrient absorption by the gut microbiota, indicating that probiotics enhance nutrient assimilation rather than appetite. 
         
The results show a significant variation in liver weight between the groups (Table 2 and 3). The liver of the control group (Group 1) weighed 58.13 g (2.73% of carcass weight), while that of Group 2, supplemented with probiotics, was significantly heavier at 69.67 g (2.44% of carcass weight). Although the difference was statistically significant (0.01<P), it was considered small based on the T-student value of 0.405. These liver weights are consistent with other studies (Awad et al., 2009; Forte et al., 2018; Zhang et al., 2021) on fast-growing broiler chickens, suggesting good nutrient storage and metabolism. 




          
The study found that while the pancreas weight of the two broiler groups differed, the difference was statistically insignificant (t=0.408, P<0.01). This is supported by the relatively low pancreas weight percentage (0.17% to 0.20%) and consistency with other studies (Mogotlane et al., 2024), suggesting a minor impact of probiotic supplementation on pancreas weight. Based on the provided text, probiotics were found to significantly promote chick growth (P<0.01), but did not have a significant effect on the weight of vital organs like the spleen. This suggests that the probiotic-enhanced growth is not leading to organ imbalances, which is a positive outcome, especially considering that the rapid growth of modern broilers can increase stress on their cardiovascular system and organs. Supporting this, the study cites other research (Awad et al., 2009 ; Idowu et al., 2025) that confirms similar spleen weight values are normal for broilers. The Student’s t-test calculation of 1.143 further validates the interpretation that there was no significant difference in organ weight. 
       
Probiotic supplementation to fast-growing broiler chickens improved their heart weight relative to body weight, suggesting the probiotics helped the heart develop sufficiently to meet the demands of rapid growth. This is significant because heart failure from sudden death syndrome is a major cause of mortality in these birds and optimal organ development is crucial for managing metabolic issues in accelerated growth lines. Therefore, including probiotics in their diet is a potential strategy to reduce mortality and improve welfare. 
       
The incorporation of 0.2% probiotics into the diet of batch 2 (group 2) significantly improved growth performance compared to the control. Live weights (3196 g vs. 2950 g), dressed weights (2852 g vs. 2700 g) and eviscerated weights (2250 g vs. 2100 g) were statistically higher than those of the non-supplemented group (Fig 2). This is because probiotics positively influence the intestinal flora, which in turn optimizes nutrient absorption and improves overall intestinal health. Consequently, this leads to faster and more efficient growth, as well as an improved feed conversion ratio. This finding is consistent with previous research, suggesting that probiotic supplementation is a promising strategy for enhancing poultry productivity (Martinez et al., 2015; Paz et al., 2019). Future research can now focus on the impact of these probiotics on the growth of vital organs, such as the liver and heart, to further meet the metabolic demands of modern broiler lines. 


 
Assessment of broiler health by blood biochemistry
 
Blood glucose
 
Control group 1 (control)
 
This group shows a steady increase in glucose levels, reaching 2.47±0.01 g/L at the end of the rearing cycle, which is above the standard (WOAH, 2022) of between 1.7 and 2.3 g/L. This increase is due to the energy-balanced diet, which promotes rapid growth, which is normal.
 
Group 2
 
Group 2, consisting of the three groups supplemented with probiotics, showed a more stable glucose level, with an average of 1.05±0.15 g/l, influenced by its energy-balanced diet. This balanced diet, combined with probiotic supplementation, helped maintain glucose levels within the normal range.
 
Impact of probiotics
 
The addition of probiotics improved glucose metabolism (Table 4) by promoting the growth of healthy intestinal flora. This reduced blood glucose levels and improved the feed conversion ratio (FCR). The FCR is the feed conversion ratio, which measures the amount of feed required to produce 1 kg of live weight. A low conversion ratio is desirable because it indicates that the feed is well assimilated by the animal.


       
An energetically balanced diet is crucial for normal glucose levels and probiotics can further optimize this by improving feed conversion and regulating blood glucose, as seen in the example of a probiotic-supplemented chicken group versus a control group. To improve blood glucose regulation, a suggestion is to incorporate probiotics into the diet alongside a balanced diet to potentially manage feed intake and enhance growth, similar to the positive results observed in group 2 of the experiment. 
       
The observed regulation of blood glucose levels by probiotic supplementation is a significant finding, as it provides a mechanism for managing metabolic health in broiler chickens. By moderating feed consumption and improving the feed conversion ratio, probiotics can prevent the hyperglycemia associated with excessive caloric intake during the finishing phase. This outcome not only promotes healthier growth but also presents a sustainable alternative to managing energetic imbalance through diet alone. The results align with previous research and emphasize the potential for probiotics to enhance overall poultry well-being and productivity (Chai et al., 2023 ; Idowu et al., 2025 ; Martinez et al., 2015). 
 
Triglycerides
 
Probiotics improved the lipid metabolism of broilers, resulting in stable serum triglyceride (Tg) levels comparable to the control group but with lower concentrations. Unlike the control group, which showed fluctuating and high Tg due to overconsumption and feed inefficiency, the probiotic-supplemented group maintained stable and lower Tg throughout growth, suggesting better digestive health and energy stability. This suggests, as established by Mirsalami et al. (2024) and Monika et al. (2024), specialists in animal production, that probiotic supplementation can mitigate the negative effects of overeating on lipid metabolism in broiler chickens. 
 
Control group (group 1): Experienced an increase in serum Tg (0.88 to 0.89 g/l) due to overconsumption of feed, which created an imbalance in lipid metabolism.
 
Probiotic group (group 2): Showed lower and more stable serum Tg levels (0.81 to 0.78 g/l) throughout the growth period.
         
Probiotics improve broiler digestive metabolism and physiological stability, which helps prevent the overconsumption issues seen in the control group and maintains stable, lower triglyceride levels (Table 4). 
 
Cholesterol
 
The analysis reveals a significant difference in cholesterol (Ch) levels between the breeding groups, with an average of 1.29 g/L for the control group and 1.04 g/L for the group receiving probiotic supplementation (Table 4). This disparity suggests that adding probiotics to the diet moderated plasma Ch levels, an observation that is consistent with the fact that dietary intake influences the concentration of this sterol, which is essential for many biological functions. The variability in plasma cholesterol levels is also influenced by genetic factors, as illustrated by the comparison between the Cobb 500 breed (from 0.8 to 1.35 g/l) and the local breeds mentioned, such as the Kabyle chicken “Thayazit n’ laqvayel” (0.9 to 1.5 g/l). It is well established that diets rich in lipids, particularly protected fats, tend to increase cholesterol levels (WOAH, 2022).
       
The authors (Martinez et al., 2015; Paz et al., 2019) confirmed that serum Ch levels increase during the growth phase, a phenomenon often intensified by unbalanced, energy-rich diets. However, in this study, the Ch levels of broilers in groups 1 and 2 were within the normal range. This suggests that specific feeding practices did not lead to hypercholesterolemia, unlike what occurs with energy-rich rations. In group 2, probiotic supplementation further improved feed conversion by regulating feed intake compared to group 1, indicating a benefit beyond simply maintaining normal Ch levels.
       
The study conducted on broiler chickens revealed that probiotics significantly affected their metabolic and blood biochemistry profiles (P<0.05). However, the effect was not consistent across different experimental batches in group 2, as indicated by a very low t-value (t=0.270). This suggests that despite the overall impact of probiotics, individual variations exist within the chicken’s gut microbiota. These individual differences are possibly influenced by factors such as genetics and diet quality. 

This study demonstrates that the controlled integration of Lactobacillus acidophilus into the diet of broiler chickens is a major performance lever for modern poultry farming. By stabilizing the intestinal microbiota, this supplementation optimizes nutrient absorption, resulting in a significant improvement in live weight, carcass yield and, above all, feed conversion ratio. Beyond growth gains, the use of this probiotic is a sustainable and effective alternative to antibiotic growth promoters, thus meeting current health and economic requirements. However, to transform this potential into an industry standard, future research will need to elucidate the fine metabolic mechanisms that govern the variability of the observed blood biochemical profiles. Similarly, a thorough assessment of the long-term impact on the integrity of vital organs (liver and heart) is essential to ensure productivity that balances zootechnical performance and physiological well-being. These prospects pave the way for precision nutrition, the cornerstone of more resilient and efficient poultry production.

I would like to thank all the staff of the Laboratory of Sciences and Techniques of Animal Production and the DGRSDT for their contribution to the development of scientific research in Algeria.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

The authors declare no conflict of interest.