This study was conducted to evaluate the effects of OAs and EOs on growth performance, serum biochemistry, antioxidant enzyme activities, intestinal morphology, and digestive enzyme activities to replace AGP in broilers. Six hundred one-day-old broilers were allotted to five treatments with six replicates: (1) negative control (NC; basal diet); (2) positive control (PC; NC + 50 mg/kg bacitracin methylene disalicylate); (3) organic acids (OA; NC + 2000 mg/kg OA); (4) essential oils (EO; NC + 300 mg/kg EO); and (5) OA + EO (NC + 2000 mg/kg OA + 300 mg/kg EO). In the starter phase, the PC, EO, and OA + EO groups had a significantly lower feed conversion ratio (FCR) compared to the NC group. While the final body weight (BW) of broilers fed OAs was similar compared to broilers fed PC (p > 0.1), the FCR of the OA group tended to be lower than the PC group on D 42 (p = 0.074). The OA group had the higher serum GLOB:ALB (albumin) and ileal villus height and crypt depth (VH:CD) ratios compared to the EO group. Thus, the supplementation of EOs and OAs could substitute AGP in the starter and finisher phase, respectively.

This study evaluated the effects of dietary 25-hydroxycholecalciferol alone or in combination with vitamin D₃ (VD₃) on growth performance, vitamin D status, immune parameters, bone integrity, and antioxidant capacity in nursery pigs. Sixty weanling piglets (5.63 ± 0.98 kg initial body weight) were assigned to three treatments for a 28 d feeding trial. The treatments were a basal diet supplemented with 2000 IU/kg VD₃, a combination of 1000 IU/kg VD₃ and 1000 IU/kg 25-hydroxycholecalciferol (25-OHD₃), and 2000 IU/kg 25-OHD₃. Pigs fed diets containing 25-OHD₃ tended to have greater feed intake during d 14–28 (p = 0.06). Plasma 25-OHD₃ concentrations were greater in pigs fed diets containing 25-OHD₃ than in those fed VD₃ alone on d 14 and 28 (p < 0.05), with greater values observed in pigs fed 2000 IU/kg 25-OHD₃ than in those fed a combination of 1000 IU/kg VD₃ and 1000 IU/kg 25-OHD₃ on d 14 (p < 0.05). Pigs fed diets supplemented with 25-OHD₃ had lower plasma malondialdehyde concentrations at d 28 (p < 0.05), while immune parameters and bone mineralization indicators were unaffected. In the broken-line analysis, the estimated plasma 25-OHD₃ concentration for plasma malondialdehyde concentrations to reach the minimum level was 32.5 ng/mL (p < 0.05). In conclusion, supplementing 25-OHD₃ in nursery diets improved blood vitamin D status and could help reduce oxidative stress during the late nursery period.