Impact of replacing salinomycin with encapsulated Lactococcus lactis EGY_NRC4 on in vitro ruminal fermentation parameters and lactating Barki ewes’ performance

This study assessed the potential of encapsulated Lactococcus lactis EGY_NRC4 as a substitute for salinomycin in the diets of lactating Barki ewes through both in vitro and in vivo experiments. L. lactis EGY_NRC4 is a newly isolated strain that has been characterized for its potential probiotic properties. The strain has been documented in the National Center for Biotechnology Information (NCBI) under the accession number MW856657. Two experiments were conducted: an in vitro study evaluating increasing doses [0, 1, 2, and 3 g/kg dry matter (DM)] of L. lactis (ELB) and salinomycin (0.35, 0.7, and 1 g/kg DM), and an in vivo trial involving 30 lactating ewes assigned to three dietary treatments (control, 2 g/kg L. lactis, or 0.35 g/kg salinomycin) for 60 days. In the in vitro study, ELB significantly increased (p < 0.05) fiber degradability, DM, and organic matter digestibility, while decreasing methane (CH₄) production linearly by up to 33.9 % and increasing carbon dioxide production. In contrast, salinomycin significantly reduced (p < 0.001) gas and CH₄ production by up to ₄8.9 %, enhancing digestibility at lower doses but reducing it at higher concentrations. In the in vivo study, both ELB and salinomycin improved (p < 0.001) nutrient digestibility, with salinomycin showing stronger effects on energy utilization. Blood parameters remained mostly unchanged, except for a significant reduction (p < 0.001) in blood urea nitrogen and cholesterol, and a slight increase (p < 0.05) in glucose levels with the use of ELB, while salinomycin had no effect on cholesterol. Both additives significantly increased (p < 0.001) milk yield by 27.0 % for ELB and 30.3 % for salinomycin, and feed efficiency by approximately 17% (ELB) and 39 % (salinomycin), though they reduced (p < 0.05) milk component content. Fatty acid composition showed minor changes, with ELB increasing (p < 0.05) beneficial unsaturated fatty acids like α-linolenic acid. In conclusion, ELB exhibited promising effects comparable to salinomycin in enhancing performance and digestibility, with distinct impacts on CH₄ emissions and milk composition.