The potential of in-ovo probiotics to replace antibiotic growth promoters in broiler diets: Effect on performance, meat quality, cecal fermentation and oxidative stress indicators

This study evaluated whether selected probiotic strains administered in-ovo could achieve performance and physiological outcomes comparable to those obtained with in-feed antibiotic growth promoters in broiler chickens. A preliminary in-ovo screening trial was conducted to identify probiotic strains and doses that did not negatively affect hatch performance. Based on this trial, two probiotic combinations were selected for an animal trial: a two-strain mixture ( Prob1 : Bacillus subtilis and Enterococcus faecium ) and a four-strain mixture ( Prob2 : E. faecium, Pediococcus acidilactici, Bifidobacterium animalis , and Lactobacillus reuteri ), both administered in-ovo on embryonic day 18 at 1.5 × 10⁷ CFU/egg. After hatch, birds were placed in a completely randomized block design and assigned to four treatments (n = 18 pens/group, 9 pens/sex, 45 birds/pen): negative control ( CTRL- ), antibiotic control ( CTRL+ , 0.5 kg bacitracin methylene disalicylate/ton of feed), and the two in-ovo probiotic treatments fed antibiotic-free diets. Growth performance, breast meat yield, meat quality traits, liver lipid peroxidation, and cecal short-chain fatty acids ( SCFA ) were evaluated. The mixed-effects model revealed that under the experimental conditions of this study, neither in-feed antibiotics nor in-ovo probiotics significantly affected final body weight, feed intake, or feed efficiency relative to CTRL- birds. However, Prob1 increased ( P = 0.014) breast meat yield compared with CTRL+ birds. Prob1 exhibited higher ( P < 0.001) breast meat ultimate pH and lower ( P = 0.013) shear force than CTRL+. Both probiotic treatments reduced ( P < 0.001) liver malondialdehyde concentrations compared with both control groups, indicating improved oxidative status. The Prob2 mixture increased ( P < 0.038) cecal butyric acid concentration on d 10, although this effect did not persist at market age. Overall, Prob2 exhibited the most consistent effects on physiological and microbial-related parameters without affecting growth performance. These results indicate that neither in-ovo probiotics nor in-feed BMD act as classical growth promoters under controlled conditions but in-ovo probiotics may support bird health and resilience. Further validation under commercial production conditions is warranted.