Abstract
Objectives: This study was conducted to evaluate the effects of graded supplementation of a commercial multi-strain lactic acid bacteria probiotic on growth performance, nutrient digestibility, and intestinal morphology in broilers reared from hatch to 35 days of age.
Materials and Methods: A total of 240 Ross 308 male broilers were distributed to four dietary treatments: a basal control diet and diets supplemented with low (1.0 gm/kg), medium (2.0 gm/kg), or high (4.0 gm/kg) probiotic inclusion rates. All data collected on growth performance, apparent nutrient digestibility, and histomorphometry were analyzed using one-way analysis of variance.
Results: Probiotic supplementation resulted in significant improvements (p < 0.05) in body weight gain and feed conversion ratio, with the highest inclusion level producing the most pronounced responses. Apparent digestibility of dry matter, crude protein, fat, calcium, and phosphorus increased (p < 0.05) in a dose-dependent manner, indicating enhanced nutrient utilization efficiency. Feed intake was reduced (p < 0.05) in probiotic-fed birds relative to controls, reflecting improved conversion efficiency rather than increased consumption. Intestinal morphometric analysis revealed significant increases (p < 0.05) in jejunum villus height and villus height-to-crypt depth ratio in response to probiotic supplementation, while crypt depth remained unaffected (p > 0.05), suggesting improved absorptive capacity without accelerated epithelial turnover.
Conclusion: These findings demonstrate that multi-strain lactic acid bacteria probiotics enhance broiler performance through combined effects on nutrient digestion and intestinal structure. The dose-dependent nature of the response underscores the importance of optimizing inclusion levels to maximize biological benefit. This study supports the use of multi-strain probiotics as an effective alternative to antibiotic growth promoters and contributes experimental evidence relevant to sustainable broiler production systems.

Key words: Probiotics; growth performance; nutrient utilization; gut health; broiler