A phytogenic feed additive blend as a replacement for monensin in lactating Rahmani ewes' diets: Effects on feed utilization and milk production

This study evaluated the potential of phytogenic feed additives (PFAs) as a replacement for monensin in the diets of lactating Rahmani ewes. Two experiments were conducted using a completely randomized design. The first was an in vitro study that evaluated the effects of increasing doses (0, 0.3, 0.6, and 1 g/kg dry matter [DM]) of PFAs and monensin. The second experiment was an in vivo trial involving 30 lactating ewes (53 ± 0.5 kg body weight), all in their first week of lactation (1–7 days in milk). The ewes were randomly assigned to one of three dietary treatments: control, 0.3 g PFAs, or 0.3 g monensin/ kg DM diet, with 10 ewes per treatment, over a 60-day period. The doses for PFAs and monensin were selected based on the optimal results observed in the in vitro experiment. Before the 60-day experimental period, all ewes underwent a 14-day adaptation period to their respective diets. In the in vitro study, both PFAs and monensin significantly reduced gas and methane production (p < 0.01), with the most substantial reductions observed at the 1 % inclusion level, decreasing by up to 17.6 % and 35.3 %, respectively. Digestibility of DM, organic matter (OM), and fiber improved at moderate inclusion levels (p < 0.01) but declined at 1 %. Additionally, short-chain fatty acids were significantly reduced (p < 0.01) with both additives. In the lactation experiment, supplementation improved nutrient digestibility, including DM, OM, crude protein, and fiber (p < 0.01), with no differences between PFAs and monensin. Blood parameters such as total protein, albumin, glucose, and cholesterol were positively influenced (p < 0.05), while blood urea nitrogen and liver enzymes decreased (p < 0.01). Milk yield, energy output, and feed efficiency improved significantly (p < 0.001), with no differences between the two supplements. The milk fatty acid profile showed reductions in total saturated fatty acids (SFA) and increases in unsaturated fatty acids (UFA), with a higher UFA:SFA ratio. Specific fatty acids, such as α-linolenic acid, increased significantly (p = 0.019). This study concludes that PFAs, at 0.3 g/kg, could effectively replace monensin to improve feed efficiency and lactational performance in Rahmani ewes.