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Gastrointestinal dysbiosis is a disturbance in mucosal homeostasis, producing low-grade chronic intestinal inflammation and impaired intestinal barrier function. It is induced by several factors, including nutrition and stress, which are both significant factors when considering current broiler breeder practices. A great grandparent (GGP) chicken meat line was identified displaying clinical signs characteristic of potential dysbiosis, including wet droppings and litter, in addition to reduced reproductive performance when compared to a consistently high performing line. This study aimed to determine whether the reduced reproductive performance observed in these hens was a result of dysbiosis and whether dietary supplementation with a Saccharomyces cerevisiae (SC) fermentation product would alleviate clinical signs. Dietary inclusion of SC did not influence intestinal permeability, WBC differentials, or corticosterone concentration in either the wet litter (WL) or high-performing (HP) breeder lines. Compared to hens from the HP line, WL line hens had a significant increase in intestinal permeability at 26 wk (onset of lay). WL hen heterophil counts were increased markedly at week 26 before declining. At weeks 26, 32, and 37 there were also significant increases in monocytes. Higher plasma corticosterone was also observed in WL hens at 37 wk. No significant differences in heterophil to lymphocyte (H:L) ratios or feather corticosterone were observed between lines. Dietary inclusion of SC supplementation to breeder diets had some benefit in regards to reducing hen mortality, improving egg production and hatchability but only in the WL line. Results from this study did not indicate that hens from the wet litter line were experiencing gut dysbiosis. Chronic intestinal inflammation may be a possible reason for the increase in intestinal permeability. These results do indicate that both breeder lines may be exhibiting physiological stress. Future investigation into the physiology and behavior around point of lay is required to find novel strategies to alleviate this stress and in turn, potentially improve welfare and production outcomes., (Copyright © 2024. Published by Elsevier Inc.)