Organic Iron Supplementation in Cows and Its Impacts on Animal Health and Production

This study evaluated whether iron supplementation in the form of chelated minerals in cows in the final third of lactation has a positive effect on iron bioavailability, immunity, oxidative status, milk quality, and biochemical and hematological parameters, as well as production efficiency and fecal microbiota. Twenty-four multiparous Jersey cows, with 210 ± 18 days in milk (DIM), an average production of 25 kg, and 4 ± 0.6 months of gestation, were divided into two groups: Control (<i>n</i> = 12, without supplementation) and Iron (<i>n</i> = 12, supplemented with 30 mg of iron/kg of dry matter (600 mg/animal/day)). Blood and milk samples were collected on days 1, 16, 29, and 42 of the experiment. Supplemented animals had higher serum iron concentrations and a higher unsaturated iron-binding capacity, especially on day 42. Higher iron content in milk was also observed. A higher granulocyte count was observed in the iron group, as well as a lower number of lymphocytes compared to the control, which may indicate immunosuppression associated with iron supplementation. Fructosamine levels were significantly lower in the iron group animals on days 14 and 28, suggesting a possible alteration in glucose metabolism. In contrast, levels of the liver enzymes AST and ALT increased significantly in the group supplemented with iron on days 28 and 42, indicating potential liver overload or injury. Iron supplementation significantly increased levels of reactive oxygen species and thiobarbituric acid-reactive substances, as well as superoxide dismutase activity in the blood. Iron supplementation altered gut microbial diversity, promoting dysbiosis characterized by increased alpha diversity and enrichment of transient colonization by <i>Nitratireductor</i>, <i>Brevundimonas</i>, <i>Flavobacterium</i> and <i>Sporosarcina</i>. Lower milk production was observed in the iron-supplemented cows in the last 10 days of the experiment, which is related to the occurrence of disease in nine cows in this group: seven with mastitis and two with intestinal peristalsis paralysis. Based on these results, we conclude that chelated iron supplementation at a dose of 600 mg/animal/day should not be used because it harms cow health and productivity.