Aflatoxins absorption in the gastro-intestinal tract and in the vaginal mucosa in lactating dairy cows

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Abstract
The objective of the experiment was to monitor plasma levels of aflatoxin B1 (AFB1), B2 (AFB2), G1 (AFG1), G2 (AFG2) and M1 (AFM1) in lactating dairy cows fed a single oral bolus with aflatoxin naturally contaminated corn meal (Trial 1). The possible aflatoxins (AFs) absorption through mucous membranes was also investigated using the vaginal mucosa (Trial 2). In trial 1, seven lactating Holstein dairy cows were given a single oral bolus of a naturally contaminated corn meal assuring an intake of 4.89 mg AFB1, 1.01 mg AFB2, 10.63 mg AFG1 and 0.89 mg AFG2. Blood samples were collected at 0 and 5, 10, 15, 20, 25, 30 minutes after treatment. In trial 2 an aflatoxin dosage similar to that of trial 1 was provided through vaginal implant to eight lactating Holstein dairy cows. Blood samples were collected at 0 and 15, 30, 60, 180, 360 minutes after treatment. Individual milk samples of six milkings, one before and five after treatment, were also collected. Plasma and milk samples were analysed by HPLC for AFB1, AFB2, AFG1, AFG2 and AFM1 contents. In trial 1 AFB1 in plasma peaked (33.6 ng/L) as soon as 20 minutes after treatment. The plasma AFM1 was already detectable at 5 minutes (10.4 ng/L) and peaked at 25 minutes (136.3 ng/L). In trial 2 only AFB1 and AFM1 were detectable in plasma, starting from the first sampling time (15 minutes), with values of 10.7 and 0.5 ng/L, respectively. The AFB1 peaked at 30 minutes (23.9 ng/L). The AFB1 excreted in milk as AFM1 had the highest concentration (203.0 ng/L) in the first milking after treatment and decreased close to the starting values after 36 hours from treatment. The prompt appearance of studied aflatoxins, and their metabolites, in plasma suggests absorption might also take place in mouth or oesophageal mucous membranes, before the rumen compartment. Results support the hypothesis that the cytochrome P450 oxidative system, which is present in these tissues and in leukocytes, could be involved in the conversion of the AFB1 in AFM1. The absorption of AFB1 through the vaginal mucosa confirms the passive diffusion as a probable mechanism for AFB1 absorption