In recent years, a rising interest has been directed towards the use of nutraceuticals in the zootechnical sector, including probiotics, prebiotics, and synbiotics, as a way to support production efficiency and cope with the increasing limitations to the use of antibiotics. In poultry, however, most studies on these products have been conducted on broilers, while less information is available on their benefits to other productive categories. The present field study aimed to assess the effects of a multi-species synbiotic product (PoultryStar® sol) on the gut health and productive performance of broiler breeders. A total of 24761 day-old Ross 308 parent stock chicks were acquired from a single hatchery and placed on the same farm. Female chicks were divided into three groups and raised in different houses (A, B, and C), in which males were introduced at the age of mating and followed until 40 weeks of age. The synbiotic was provided by drinking water to the flocks in houses A and B, while house C was kept as control. Following the manufacturer’s guidelines, the product was administered intermittently once every two weeks, except in the first and the twenty-first week when it was supplied for three consecutive days. Data on performance parameters, egg quality traits, bacterial enteritis scoring, intestinal morphometry, and histopathology were recorded, and the caecal content was collected at 15, 25, and 40 weeks of age to investigate the intestinal microbiota using high-throughput next-generation sequencing. Synbiotic-treated hens showed significantly higher survivability during production compared to the control group. No clear differences were observed between treated and control chickens in terms of egg production and quality, and the effect of the synbiotic on weight gain also appeared limited. From 25 weeks onwards, synbiotic-treated chickens scored better in terms of macroscopical lesions and had longer intestinal villi. Significant differences in crypt length and histopathological lesions were also found at multiple sampling points. A treatment effect on caecal bacterial composition was detected with a differential abundance of Gastranaerophilales, Lachnospiraceae, Helicobacter, Ruminococcaceae, and Clostridia, among others. Taken together, obtained results support the beneficial effects of the intermittent administration of the synbiotic product PoultryStar® sol on the gut health of broiler breeders. Keywords: Broiler breeder, Gastrointestinal health, Histopathology, Microbiota, Synbiotic