Previous studies have suggested the use of probiotics, as alternative to antibiotics, to enhance broiler performance. The administration of probiotics in feed has been widely explored; however, few studies have evaluated the in ovo inoculation of probiotics. Therefore, the objective was to evaluate the impact of in ovo inoculation of different concentrations of GalliPro Hatch (
GH
), an
Enterococcus faecium
–based probiotic, on hatchability, live performance, and gastrointestinal parameters. Ross x Ross 708 fertile eggs were incubated, and on day 18, injected with the following treatments: 1) 50 μL of Marek's vaccine (
MV
), 2) MV and 1.4 × 10
5
cfu GH/50 μL, 3) MV and 1.4 × 10
6
cfu GH/50 μL, 4) MV and 1.4 × 10
7
cfu GH/50 μL. On the day of hatch, chicks were weighed, feather sexed, and hatch residue was analyzed. Male birds (640) were randomly assigned to 40 floor pens. On day 0, 7, 14, and 21 of the grow-out phase, performance data were collected. One bird from each pen was used to obtain yolk weight and intestinal segment weight and length. Hatchability was not impacted by any GH treatment (
P
= 0.58). On day 0, yolk weight was lower for all treatments than for MV alone. On day 0 to 7, feed intake was lower for 10
5
and 10
7
GH; the feed conversion ratio (
FCR
) was lower for all treatments than for MV alone (
P
= 0.05;
P
= 0.01, respectively). From day 14 to 21, the 10
7
GH treatment had higher BW gain (
P
= 0.05). For day 0 to 21, 10
7
GH had a lower FCR than MV alone (
P
= 0.03). On day 0, all GH treatments resulted in heavier tissues and longer jejunum, ileum, and ceca lengths than MV alone (
P
< 0.05). Spleen weight was higher for 10
5
and 10
7
GH than for MV alone. In conclusion, GH does not impact hatchability, and some concentrations improved live performance through the first 21 d of the grow-out phase. These improvements could result from the increased yolk absorption and improved intestinal and spleen morphology seen in this study.
