In Ovo Folic Acid Injection Modulates Hatchability, Hematobiochemical Profiles, Immune Status, and Intestinal Histomorphology of Day-Old Broiler Chicks

This study evaluated the effects of in ovo folic acid administration on hatchability, physiological profiles, and intestinal development in day-old Cobb broiler chicks. A total of 600 embryonated eggs were assigned to five treatments: an uninjected control, a saline control, and three folic acid levels (50, 100, and 150 µg/egg) injected into the amnion on day 18 of incubation. Folic acid administration significantly improved hatchability, with 50 and 100 µg/egg achieving higher rates (98.83% and 99.45%) than the control (98.06%; p = 0.0405), alongside a linear increase in chick length (p = 0.0097). In contrast, egg weight, chick weight, and chick yield were unaffected (p > 0.05). Folic acid stimulated linear increases in the relative weight of the bursa of Fabricius, total white blood cells, lymphocytes, and serum IgM concentrations (p < 0.05). Erythrocyte counts, hemoglobin, and packed cell volume also increased linearly (p ≤ 0.0003). Serum biochemical profiling revealed linear increases in total protein, albumin, and thyroid hormones (T3 and T4), alongside linear declines in glucose, cholesterol, and creatinine (p ≤ 0.0028). Additionally, folic acid supplementation reduced serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Systemic oxidative stress was reduced, marked by decreased malondialdehyde (MDA) and enhanced total antioxidant capacity (TAC) and glutathione peroxidase (GSH-Px) activity (p < 0.05), peaking at 100 µg/egg. Furthermore, intestinal villus height, crypt depth, and surface area were significantly increased (p ≤ 0.0003), peaking at 100–150 µg/egg. Collectively, these findings indicate that in ovo folic acid supplementation supports physiological adaptation during the peri-hatch period and promotes intestinal development in newly hatched broiler chicks. It is recommended that modern hatcheries utilize an optimal dosage within the range of 100 to 150 µg/egg during late incubation to maximize hatchability, immune function, antioxidant defenses, and gut absorptive capacity.