Diagnosis of Subclinical Aflatoxicosis by Biochemical Changes in Dairy Cows under Field Conditions

Aflatoxins (AF) are potent mycotoxins with carcinogenic, teratogenic, and mutagenic potential. There is no agreement on the safe AF maximum residue levels established in different countries (5.0 to >20.0 μg/kg) to avoid feed toxicity in dairy cows and to protect the food chain. The objective was to establish a diagnosis of subclinical aflatoxicosis via changes in biochemical values during long-term exposure of AF low concentrations under field conditions. A cohort of 90 Holstein heifers were selected (395±10 kg/BW; 14-15 months) in a large dairy farm in the central Mexico highlands. Monthly samples of blood serum, feedstuffs, total mixed ration, and raw milk were obtained (26 months) and analyzed via spectrophotometric and HPLC methods. Dairy diets were naturally contaminated with AF (8.1±5.2 µg/kg). No cow showed clinical disease, but significant changes in biochemistry values were associated to AF intake at levels >5.0 µg/kg, especially a serum concentrations decrease in albumin, total protein and reduced glutathione; furthermore, an increase in prothrombin time, and in specific activity of AF metabolizing enzymes (glutathione S-transferase, γ-glutamyl transferase, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase). Raw milk samples were naturally contaminated with AF in milk (AFM1; 43.1±24.0 ng/kg). A linear dose-response relationship between AF in feed and AFM1 concentrations was observed (AFM1=19.2+2.70(AF); P<0.01; R2 :62.1%). Moreover, reproductive failure and inter-pregnancy interval rates of cows exposed to higher AF concentrations (>10.0 µg/kg) were increased. These results suggested that in the long term, low amounts of AF exposure may lead to significant adverse effects consistent with subclinical aflatoxicosis.