Dose-Dependent Effects of Probiotics on the Reproductive Performance, Egg Characteristics, and Seminal Traits of Broiler Breeders: A Model-Based Meta-Analysis

Probiotics are increasingly used in poultry nutrition because of their potential to improve performance and reproductive outcomes. However, there is limited consensus on the effectiveness of different probiotic strains and formulations in broiler breeder hens. This meta-analysis aimed to evaluate the impact of various probiotics on broiler breeder performance and reproductive traits. A comprehensive data set on probiotic supplementation in poultry broiler breeder hens (of different strains) was compiled spanning the time period from 1990–2024. The effect size (Hedge's g) of probiotics was analysed to estimate the random and fixed effects of study variations. Among the rooster strains, the Hubbard strain presented a significant reduction in the number of dead sperm (p < 0.01). Moreover, multistrain probiotics were found to be more effective than single strains (p < 0.01). In hens, probiotics were associated with a significantly lower feed conversion ratio (FCR) (p < 0.001), as were improvements in the fertility and hatchability of settable eggs (p < 0.001). In particular, the addition of probiotics derived from Bacillus subtilis significantly increased fertility and hatchability (p < 0.001). In summary, both single-strain and multistrain probiotics significantly increase various reproductive and performance parameters in broiler breeders, with multistrain probiotics consistently showing superior effects across multiple areas. The inclusion of multistrain probiotics up to 1 g/kg generally yielded positive effects on several parameters in broiler breeder hens. These findings support the inclusion of probiotics, particularly multistrain formulations, to increase reproductive efficiency and performance in broiler breeders, providing a sustainable alternative to antibiotics.