Antibiotic growth-promoters in animal feeding are known to generate bacterial resistance on commercial farms and have proven deleterious effects on human health. This review addresses the effects of probiotics and their symbiotic relationship with the animal host as a viable alternative for producing healthy meat, eggs, and milk at present and in the future. Probiotics can tolerate the conditions of the gastrointestinal tract, such as the gastric acid, pH and bile salts, to exert beneficial effects on the host. They (probiotics) may also have a beneficial effect on productivity, health and wellbeing in different parameters of animal performance. Probiotics stimulate the native microbiota (microbes that are present in their place of origin) and production of short-chain fatty acids, with proven effects such as antimicrobial, hypocholesterolemic and immunomodulatory effects, resulting in better intestinal health, nutrient absorption capacity and productive responses in ruminant and non-ruminant animals. These beneficial effects of probiotics are specific to each microbial strain; therefore, the isolation and identification of beneficial microorganisms, as well as in vitro and in vivo testing in different categories of farm animals, will guarantee their efficacy, replicability and sustainability in the current production systems.

Five strains (CLP2, CLP3, CLP4, CLP5, and CLP6) were isolated from the cecal content of Creole roosters fed without antibiotic growth promoters. Biochemical and morphological tests (negative catalase and oxidase) confirmed the presence of lactic acid bacteria. Additionally, considering the 16s RNA, Lactobacillus vaginalis (CLP2, CLP3, CLP5, and CLP6) and Lactobacillus reuteri (CLP4) were identified. All strains (mainly CLP4 and CLP5) showed variable and significant growth (p < 0.001) at different levels of pH. Likewise, all bacterial cultures were quantified at 42 °C, although only strains CLP4 and CLP5 managed to grow at 30 °C. Additionally, the CLP4, CLP5, and CLP6 strains grew from 0.05 to 0.30% of biliary salts. However, only the CLP4 isolate grew at different concentrations of NaCl (2–10%), and CLP5 grew at 2% NaCl. The CLP4 strain was able to inhibit the in vitro growth of enterobacteria such as Escherichia coli ATCC^® 11775TM, Salmonella Typhimurium ATCC^® 14028TM, and Clostridium perfringens ATCC^® 13124TM. In addition, CLP4 had lower sensitivity in the presence of amoxicillin and tetracycline compared to these pathogenic bacteria. Considering these in vitro results, it is necessary to carry out in vivo studies with the CLP4 strain to test the hypothesis of its probiotic effect in poultry.

In recent years, the poultry industry has actively sought more sustainable feed additives to address the various challenges of intensive production. To evaluate the oral effect with Lactobacillus reuteri CLP4 on performance, carcass traits, organ weights, cecal microbiology, tibial mineralization, blood indicators, and nitrogen and phosphorus excretion in broilers, 800 one-day-old unsexed Ross 308^® chicks were randomly assigned to two treatments: a basal diet (T0; BD) without additives and BD+Lactobacillus reuteri CLP4 (T1) in the drinking water during the period from 0 to 21 days old. T1 decreased feed intake and feed conversion ratio without affecting body weight or viability of broilers. Likewise, it diminished abdominal fat and improved breast protein content. The probiotic also increased the relative weights of the thymus, spleen, liver, and pancreas, decreased the population of Salmonella spp. and cecal pH, and promoted the growth of lactic acid bacteria. Moreover, T1 improved serum immunoglobulin concentrations and decreased harmful serum lipids and nitrogen excretion, although without modifying the moisture, calcium, and phosphorus content of the tibia or phosphorus excretion. Oral supplementation with Lactobacillus reuteri CLP4 enhances productivity, breast protein, immune function, atherogenic index, cecal competitive exclusion, and reduces the environmental nitrogen load in broiler production.