Protective Effects of a Rosemary (Rosmarinus officinalis L.)-Based Phytogenic Feed Additive Against Aflatoxin B1 in Diet-Challenged Broiler Chickens

Aflatoxin B1 (AFB1) is a major mycotoxin in poultry feeds that can impair growth and damage multiple organs. This study evaluated whether dietary rosemary (Rosmarinus officinalis L.) could mitigate AFB1-induced alterations in broiler chickens. Forty-five one-day-old male Ross 308 broilers were assigned for 21 days to a control diet, a diet containing 250 µg/kg AFB1, or the AFB1-contaminated diet supplemented with 0.5% rosemary. Growth performance, relative organ weights, hematologic and serum biochemical profiles, hepatic and renal histopathology, and intestinal and glomerular morphometry were evaluated. AFB1 significantly reduced body weight on day 14 (p = 0.028), worsened feed conversion ratio on days 7 and 14 (p = 0.001 and p = 0.011, respectively), decreased feed intake on day 21 (p = 0.004), and reduced relative bursal weight (p = 0.036). Rosemary supplementation significantly improved feed conversion during the first two weeks and restored feed intake on day 21 to values comparable with the Control group. Although body weight in the AF+PHY group was 22.3% higher than in the AF group on day 14, this pairwise difference was not statistically significant; nevertheless, the magnitude of this numerical response may be practically relevant by reducing early AFB1-associated performance losses. AFB1 also increased hepatic and glomerular lesion severity and reduced duodenal villus height (p = 0.012) and villus-plus-crypt length (p = 0.006). Rosemary significantly reduced bile duct epithelial degeneration (p < 0.001), overall hepatic lesion severity, and glomerular obliteration (p < 0.001), reducing the mean glomerular obliteration score by 41.3% relative to the AF group (1.55 vs. 2.64), while preserving duodenal villus-plus-crypt length at values not significantly different from the Control group. These findings indicate that 0.5% dietary rosemary partially mitigates AFB1 toxicity, with statistically supported improvements in feed efficiency and attenuation of selected hepatic, renal, and intestinal structural alterations.