**4. Effect on growth performance**

It has been theorized that probiotics can help poultry birds continue their typical development and functioning by serving as a source of vitamins, nutrients, and digestive enzymes that have a beneficial impact on feed utilization, nutrient absorption, and growth rates. Various commercial probiotic supplements have been tested for their growth-promoting effects in poultry. Studies have demonstrated that probiotics such as *Bacillus subtilis* and Lactobacillus species have the potential to improve feed conversion ratios (FCR) and increase body weight gain in broilers. These effects are attributed to the mechanisms mentioned earlier, which collectively lead to optimized nutrient utilization and enhanced growth rates. Zymospore® (Vetanco Brazil, *B. subtilis*), a commercially available direct-fed microbe, increased the bacterial variety of the broiler's gut microflora evidenced by heightened levels of lactic acid bacteria and clostridiales, thereby promoting feed digestion and growth, even under experimentally challenging conditions [18]. Broiler chickens given commercial probiotics (Lacto sacc, Alltech, Inc.) showed a considerable feed conversion ratio, as determined by Georgieva et al. [19].

In addition to single-strain probiotic supplements, herbal probiotic additives have also been explored for their growth-enhancing properties. These additives often combine beneficial microorganisms with herbal extracts, creating a synergistic effect on growth performance. For example, a study reported significant effect on weight gain in broilers provided with diet supplemented with Promix® (*B. subtilis*, *Bifidobacterium bifidum*, *Bifidobacterium longum*, *Lactobacillus acidophilus*, *S. cerevisiae*) and herbs (*Curcuma xanthorriza*, *Curcuma aeruginosa*, *Zingiber offocinale*, *Curcuma domestica*, *Kaempferia galanga*), a commercial herbal probiotic feed additive [20]. When challenged with Salmonella pullorum, a recent study observed significant effect (*P ≤* 0.05) on feed intake, mortality, and gut microflora in dwarf male chicks fed with basal diet supplemented with probiotic fermented herbal blend [21].

Nutrient adequacy and nutrient deficiency conditions controlling the probiotic growth. In cases of nutrient deficiency, probiotics assist in enhancing nutrient absorption and utilization, effectively compensating for reduced nutrient availability in the diet. This suggests that probiotics could play a crucial role in improving growth rates even in challenging dietary situations. A study observed, significant improvement in Feed conversion ratio (FCR), Feed intake (FI) and on weight gain (WG) in broiler hens fed with triticalate-based diet enriched with probiotics and enzymes [22]. The ileal digestibility coefficient of proteins, starch, and gross energy all improved significantly (P *≤* 0.05) when the probiotic (*Bacillus subtilis*) was added to the broiler diets of both nutrient-adequate and nutrient-deficient birds [23]. Similarly, significant (*P ≤* 0.01) increased in body weight and decreased FCR was observed in chicks fed with meal supplemented with *Bacillus subtilis* probiotic, the results were in comparison with conventional feed additive—bacitracin methylene

### *Advances on Probiotics Utilization in Poultry Health and Nutrition DOI: http://dx.doi.org/10.5772/intechopen.113738*

disalicylate (BMD). However, when challenged with *E. coli*, both *B. subtilis* and BMD did not compensate for the growth deterioration in chicks [24]. A study showed that the overall performance of white Pekin ducks was enhanced when a probiotic combination of *L. acidophilus* and *Lactobacillus casei* was added to a diet low in protein [25]*.* Bidura et al. reported that enrichment of basal diet with probiotics, *Saccharomysces sp.* Increased growth performances along with decreased levels in serum and meat cholesterol in male duckling [26]*.* It has been found out that dietary supplementation with probiotics*, Pediococcus acidilactici* and *B. subtilis* in water, improves the intestinal health and resistance of chickens against coccidiosis-causing *Eimeria species* [27].

In contrast, as in Ref. [28], it was discovered that supplementing with probiotics had no discernible effect on chicken carcass, growth performance or meat quality. Recently, endeavors have been directed towards the identification and isolation of lactic acid bacteria possessing probiotic capabilities, to engage in interactions, whether direct or indirect, with aflatoxin-producing fungi, or to detoxify aflatoxins themselves. A study reported beneficial effect of probiotic, *Lactobacillus plantarum* 299v in subsiding the toxic effect of poultry fed contaminated by aflatoxins [29]. According to research, supplementing the diets of dual-purpose hens with the probiotics *Lactobacillus paracasei sparacasei* and *Lactobacillus rhamnosus* significantly (*P <* 0.05) increased both body weight gain and FCR [30]. Khabirov et al. postulated that supplementing broiler feed with Normosil, i.e., live cultures of *Lactobacillus* and *Enterococcus* strains improved overall growth, nutrient digestibility and hematological characteristics [31]. Another study reported that *Bacillus licheniformis* as probiotic in basal diet showed better improvement in broiler chickens' body weight gain and production efficiency factor in comparison with *Bacillus subtilis* [32].


The effects of Probiotics on poultry's growth performance are summarized in **Table 1**.


#### **Table 1.**

*Probiotics' effects on poultry.*
