Dietary Supplementation with Rumen-Derived Streptococcus macedonicus Improves Growth Performance and Carcass Characteristics of Barki Lambs

This study evaluated a rumen-derived Streptococcus macedonicus isolate in Barki lambs using in vitro and in vivo approaches. The isolate was characterized for antibacterial activity and antimicrobial susceptibility. In vitro, a control diet was incubated for 24 h with 0, 0.002, 0.004, 0.008, or 0.016 g of S. macedonicus, and fermentation and digestibility were determined. In vivo, 40 Barki lambs were assigned to four dietary treatments for 210 d: control, control plus 1 g/d commercial probiotic, or control plus 1 or 2 g/d S. macedonicus. Feed intake, nutrient digestibility, growth performance, carcass traits, and meat quality were evaluated. The isolate showed antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, and Bacillus cereus. In vitro, S. macedonicus increased dry matter digestibility (52.9% to 56.7%; p = 0.042) and total gas production (p < 0.0001). In vivo, dry matter digestibility increased from 66.3% to 75.2% (p = 0.002). Supplemented lambs had greater final body weight, average daily gain, and an improved feed conversion ratio (p < 0.001). Supplementation also improved carcass yield, dressing percentage, longissimus muscle area, lean proportion, water-holding capacity, and meat redness while reducing carcass fat percentage. Overall, rumen-derived S. macedonicus improved nutrient utilization, growth performance, and carcass and meat quality traits.